Finder Chart: Visualization

All of the interactive image visualization tools work the same basic way, and here we describe these basic options, in roughly the order in which you might encounter them in the window.

Critical to many of the functions described in this visualization section is the concept of the "selected image." Finder Chart can return up to 34 images of the same patch of sky. Look at the array of images returned by a search. One (you may have to look for it) is "selected" -- it is outlined in brown. Click on a different image, and that image becomes outlined in brown as the selected image. By default, the Finder Chart images are locked together, so quite often what you do to one image is done to all the images. But certain other behaviors described here are still customized to each individual image. In order to affect a given image, you must select it.

Contents of page/chapter:
+FITS Viewer
+Image Information
+Breaking Out of the Pane (and Going Back)
+Image Navigation
+Image Toolbar
+Color Stretches
+Image Layers: Viewing/Changing the Layers on the Image
+3-color images
+Extraction Tools
+Region Selection
+Footprints
+Examples of Catalogs and Layers

FITS Viewer

You can change the units of what is being read out, in terms of coordinates or pixel values.

If you click on the label of the coordinates, "EQ-J2000" in the screenshot example above, you get this pop-up, from which you can choose the coordinates from among: Equatorial (RA/Dec) J2000 in hh:mm:ss ddd:mm:ss format Equatorial (RA/Dec) J2000 in decimal degrees Galactic in decimal degrees Equatorial B1950 Ecliptic J2000 Ecliptic B1950 FITS Image Pixel Zero-based Image Pixel If you click on the "click lock" toggle, the coordinates stop dynamically updating when you move your mouse, and they update only when you click on the image. When you do that, little clip boards appear next to each coordinate readout; clicking on those copy the position to your clipboard. From this pop-up window here as shown, you can control the format of the coordinates that are copied to your clipboard -- they can be as shown in the readout, or in the format that Python is expecting (for easy pasting into code).

Click on the label of the readout, "Flux" in the tiny snippet of a screenshot example above, and you get this pop-up, from which you can choose the pixel readout from among: Integer data readout in decimal Integer data readout in hexadecimal Floating point data readout in decimal Floating point data readout in hexadecimal If you choose the hexadecimal options, it will suppress all rescaling corrections found in the header, like BZERO or BSCALE. It will just show you the raw binary number in the file. (For example, if the value in decimals is 5.13795757, the binary value in the file is 0x40a46a26; here is a conversion tool between decimal and hex.)

In the lower left of the images, if you click on this: , you get this pop-up. At the top of this pop-up, it shows the whole image; the orientation of the image is given with a compass rose. There is also a zoom-in of the image at the location under your cursor. Underneath that in the pop-up, you can get a readout of the pixel size, a readout of location on the image in two different coordinate systems, and a readout of the pixel value. You can change the units of those values by clicking on the name of the field: "Pixel Size", "EQ-J2000", "Image Pixel", and "Value". Each results in a pop-up, as above.

You can make the cursor 'stick' on a particular place on the image -- flip the "Click Lock: off" switch to "on" (either in the pop-up or in the lower right of the image window), and then click on the image at your desired location. When this is clicked, small "clipboards" appear near the position readout. Click on that icon to copy that position to your clipboard.

Image Information

Example of image label. Note that it contains information about the survey, band, date obtained, and current field of view ("FOV").

The target on which you searched is overlaid on the main image with a cross-hair marker, sometimes called a "reticle." You can remove this (or change its color) from the layers pop-up, described below.

Make it big! For some purposes, it is useful to individually view just the table, or the images, or the plots, as large as possible. In any pane, this icon appears in the upper right of the pane. Clicking on it will expand the pane into a larger window, as big as possible given your browser size.

Go back the way it was: The large "Close" arrow at the upper left is always available in the expanded views, and enables you to return back to the pane view.

Special case of images only: If you have only images loaded in, then the images are taking up all of your browser window, and it is already, by default, in this expanded mode. There's no 'close' arrow in the upper left since there is nothing else loaded in. You can, however, view one image at a time -- see next section on image navigation.

Single or Tiled Images

When you have many images loaded in, you can have icons like this: that portray (in icon form) the different views you can have of the images you have loaded. The first icon (the big square) denotes "show one image at a time." The second icon (the cluster of four squares) denotes "show smaller images of all the images I have loaded at once," e.g., tiled images. Whether the images (tiled or not) take up all the space or not depends on whether you are viewing in panes or in the full-screen mode (see immediately above on Breaking out of the pane).

Paging through single image views

If you have many images loaded in and click on the single big square to view one image at a time, you are provided with navigation aids in the top of the images window, like this:

The arrows allow you to scroll through your list of images, sorted as originally shown in the search results.

Scrolling through multi-image views

When you have several images loaded in and click on the cluster of four squares to view them all at once, chances are very good that you will not be able to see all the images without scrolling. You can use your mouse to scroll through the collection of images. If you are on a Mac, your scrollbar may be hidden until you try to scroll.

⚠ Tips and Troubleshooting: If your mouse is in a currently active (selected) image (that is, highlighted in brown), then your image will zoom rather than scroll. Just move your mouse over to another image, and then your window will scroll rather than zoom. Or, find your scrollbar.

Image Toolbar

This is the image toolbox when you have clicked on a FITS image you have loaded:

Many of the icons have a downward pointing black triangle, which means that there are additional options in a drop-down menu that appear when you click on the icon.

We now discuss each icon in the order in which they appear.

Tools drop down

The choices here look like this:

jump to save jump to rotate jump to layers jump to extract

Saving the image

The diskette icon will allow you to save the current image. You can save files to your local disk or to the IRSA Workspace . Note that you control where the file is saved on your disk through your browser; your browser may be configured to store all downloads in a particular location on your disk.

You can save images as FITS, PNG, or regions files to your local disk. Saved FITS images will not save the color stretches or overlays; it will just save the underlying FITS image. Saved PNG files WILL include the image as shown with any overlays or annotations you have placed on the image, but will not include the underlying FITS image. Saved regions files will not save the underlying image, but will just save the overlays as a DS9 Regions file. See the DS9 website for more information on the syntax of these DS9 region files.

Note that you can save the original or a cropped version of a FITS file; see the "select region" icon below to crop, then click on the save icon. Be sure to save the cropped FITS image (see annotated figure).

Note that if you overlay a large catalog on an image, then turn around and save a regions file from the catalog overlay, the full catalog may not be saved to the regions file. If you have >5,000 sources, it's entirely likely that not every source will be overlaid on the image (because of hierarchical catalogs display), and thus will not be in the regions file. If you want to save your entire catalog as a regions file, save the catalog from the table pane.

The saved PNG is the same size as it is on your screen. If you want a big version, make the desired image big on your screen (view one-at-a-time; see here) before saving the PNG.

Restoring everything to the defaults

If you've played around a lot with the image, you may want to undo everything you've done. Click this button to restore everything to their original default values. Some layers may persist; remove them via the layers icon.

Viewing the image header

This icon displays a pop-up window with the FITS header. This is shown as a Firefly table like all the other tables in this tool, so it is sortable and filterable, etc. If you click on the columns in the pop-up, it will sort the keywords alphabetically by that column. This is useful for finding individual keywords in particularly densely populated FITS headers. Click the header again to sort in reverse-alphabetical order, and a third time to return to the default order. Below are examples of an original and sorted FITS header. To make this window go away, click on the 'x' in the upper right of the pop-up, or click "close" on the bottom left.

Rotating the image so that North is up

Images retrieved in Finder Chart are already oriented such that North is up. However, when interactively investigating images, you could find yourself in a situation where North is not necessarily up. Clicking this icon will orient the selected image so that North is up.

Flipping the image on the y-axis

Clicking on this icon flips the image on the y-axis. (This option is only available for FITS, not HiPS, images.)

Add a compass rose

When you click this icon, arrows appear on the image showing which direction is North and which is East. Clicking on this icon a second time removes this compass rose. (You can also remove this layer via the layers icon, described below.)

Add a coordinate grid

Click on this icon to overlay a coordinate grid on the image. Click it again to remove it. Customize the units of the grid (to, e.g., Galactic coordinates) via the "layers" icon (described below).(Also see information on HiPS grid in the WCS section.)

Measuring a distance

When you click this icon, at first, nothing seems to happen. However, you can now click and drag to draw a line on the image, and the length of the line is displayed (in the middle of the line). The units for the measured distance (and the color of the overlay) can be changed from the "layers" icon (described below). You can calculate the difference in RA and Dec separately via the layers icon as well; find the layer associated with the distance measurement and tick the "offset calculation" box. When it displays the offset calculation, it will give you the angle in degrees in one corner, and the length of the line segment in the RA and Dec directions, in the units you have specified. When you are done with the distance tool, you can click on the that appears next to the image toolbar, or click on this icon a second time to remove the distance tool. (You can also remove this layer via the layers icon.)

Read in a DS9 Regions file

When you click this icon, you get a pop-up window from which you can read in a DS9 regions file from your local disk. See the DS9 website for more information on the syntax of these DS9 region files. The supported regions are text, circle, box, polygon, line, and annulus. To make this window go away without doing anything, click on the 'x' in the upper right of the pop-up.

⚠ Tips and Troubleshooting: If you overlay a list of sources you created in ds9 regions format from your disk, it will only be overlaid on the current image, not all of the images you have loaded. If you want to have it overlaid on all the images you have loaded, create a catalog from your source list and overlay it as a catalog. Then it will appear on all of the images you have loaded, provided that the positions overlap on the sky.

Put a marker on the image

When you click this icon, a drop-down menu appears with several possible options:

The first overlay choice (simply called 'marker') is a red circle. Initially, it appears in the center of the images, and is meant to be moved to wherever you first click in the image. It looks like this:
. The dash-dot line around it means that it is 'active', so you can move (click and drag the marker) or resize it (click and drag the dash-dot boundary). You can change the color of the marker (and change the label) via the "layers" icon (described below). You can also remove this layer via the layers icon. There are several additional options in the drop-down, enough that they have their own section below.

Drill down through the image

If your FITS image has multiple planes or HDUs, especially if each plane or HDU represents a different wavelength, it can be useful to "drill" down through the image cube at a given position on the sky. (You are unlikely to find this kind of file in Finder Chart.) This tool allows you to do just that. When activated, this tool extracts the data at the place your mouse clicks down through the cube. For more information on saving the information, see the extraction section below.

Draw a line in the image

When this tool is activated, you can draw a line in your FITS image with your mouse, and it will extract for you the pixel values along that line. If you have more than one image loaded and visible, you can shift-click in another image to see the same line in another image. For more information on saving the information, see the extraction section below.

Make points in the image

When this tool is activated, you can click in your FITS image with your mouse, and it will extract for you the pixel values at the location of your click, creating a catalog for you as you click. If you have more than one image loaded and visible, you can shift-click in another image to extract points from another image. For more information on saving the information, see the extraction section below.

Zoom

When your mouse is in an image, these options appear in the upper left of the image.

Zooming in or out

Clicking on these magnifying glass icons zooms in or out of the image. The readout of the net effect of your zooming on the displayed field of view (FOV) appears at the top left of each image.

If you click zoom in or out rapidly, a pop-up window appears to allow you to more rapidly select the zoom level (field of view) you want. Select the desired level, or click on the 'x' in the upper right to make the window go away. Here is an example:

You can alternatively zoom using the mouse wheel (or drag forward and backward on a touchpad or magic mouse).

Note that there is a maximum (or minimum) allowed zoom level. A notification will appear when you have reached the maximum (or minimum) allowed zoom level for a given image. To enlarge images more (or less) than that, please repeat your search to obtain new images with smaller (or larger) spatial extent.

Fit image to screen or fill screen

These two icons are designed to maximize the available space in your browser window. The first one automatically picks a zoom level such that the image entirely fits within the available space (which could be your whole browser window, or just the portion of it where that image is loaded). The second one automatically picks a zoom level such that the image fills as much of the available space as possible (e.g., it is zoomed such that short axis of the window is filled with the image, whether that short axis is left-right or up-down).

By default, the images that are returned are frequently but not always centered on your search target. Clicking on these icons let you see the whole image that is returned, whether or not it is centered on your target.

Zooming to a 1-to-1 size

Clicking this icon will zoom the image such that one pixel in the image is one pixel on your screen.

Color table drop down

This icon enables you to change the color table of the displayed image. When you click the button, a drop-down menu appears.

The top of the menu either says "Color and overlays locked" or "Color and overlays unlocked" -- by default, all of the FITS images that you have loaded are locked together for color and overlays. What that means is if you change the color table (via this menu), then the color table for all the FITS images are changed. (Or, if you add a layer to one image, then the layer is added to all the images; see below.) If you don't want this to happen, select "Color and overlays locked" to unlock it. Select the text again to lock it again. The arrow in the upper right creates a pop-up window out of this drop-down menu so that you can leave the choices up while settling on the best option. The next portion of the menu has a wide variety of color table choices. Select your new color table from the options shown. The sort of swirly, hurricane-like icon at the end of each color table means "invert this color table." If you click on this icon, it will invert the specific color table and then implement it in your image(s). Alternatively, you can use the "color bar" slider to move among the color tables by number. These numbers correspond to the color bar number used in the Python implementation of the Firefly tools. Pixels that are NaNs in the image are portrayed as the color shown by the swatch next to "NaN Pixel Color (Auto)." The tool is finding a color that is most different from the colors used in the image(s) as currently shown, and using that to render the NaNs in the image. If you want to change that, click on the color swatch to bring up a pop-up from which you can click on a different color, enter the hex code, OR enter the RGB numerical values; the color you pick will persist until you pick a different color table: At the bottom, there are sliders controlling the bias and contrast. Click or drag the slider to change the image display.

Color stretch drop down

This icon enables you to change the color stretch of the displayed image. Because this is complicated, for much more information, please see below.

Re-center the image drop down

Clicking this icon produces a drop-down menu:

The nature of this Finder Chart tool is that you have small region(s) of sky centered on your target(s) as specified in your search. But, it could be that you are zoomed into a different part of the image and want the tool to center on the target, or the image, or on coordinates that you enter here. This menu is how you do that.

Selecting a region drop down

When you click this icon, you can select a region of the image for further actions. Because this is complicated, for much more information, please see below.

Image Layers: Viewing/Changing the Layers on the Image

Every time you add something new to the image, you add a 'layer' to the image. This is complex, so please see below for much more information.

Lock/unlock images

This "lock images" icon appears locked initially for Finder Chart; the second icon is what it looks like when unlocked. The main purpose of this icon is to lock all the images you have loaded for zooming, scrolling, etc. You can specify how it locks and for how long. Clicking it produces this drop-down menu:

The first set of options aligns the images only once, temporarily; the second set of options makes the alignment persist ("lock") when you move the images (that is, when you move one, they all move). By default in Finder Chart, all the images are aligned and locked by WCS. You can align by the images' WCS (e.g., RA and Dec), by the target, by the pixels according to the origin of the coordinate system in the image header, or by the pixel at the image center.

Getting help

Clicking on this icon, whereever it appears, takes you to this help page.

The top of the menu either says "Color and overlays locked" or "Color and overlays unlocked" -- by default, all of the (FITS) images that you have loaded are locked together for color and overlays. What that means is if you change the color stretch (via this menu), then the color stretch for all the (FITS) images are changed. (Or, if you add a layer to one image, or change the color table of one image, then the change is made to all the images; see other sections of this chapter.) If you don't want this to happen, select "Color and overlays locked" to unlock it. Select the text again to lock it again.

Example: Display the pop-up for color stretch. From the main drop-down, pick 'Linear stretch to 99%'. Go back to the color stretch pop-up. Note that it has filled out the stretch type and ranges to reflect the current choice. Then -- either with the pop-up window still up or not -- go back and pick a different pre-defined stretch from the standard options. Note that the values in the pop-up change to reflect this current choice. From the pop-up, pick a different stretch type -- try "histogram equalization." Select "refresh" to update the images. Go back to the drop-down menu. The last 7 items have changed to be based on histogram equalization, as opposed to the "linear" default.

If you have a 3-color image, you can change the stretch in each color plane separately; select the tab at the top accordingly for red, green, or blue. By default, it stretches each band independently, and you can set the parameters in the stretch pop-up accordingly.

As described in Lupton et al. (2004) , a different algorithm may be useful for creating 3-band color images. Select "Hue preserving stretch" to invoke this option. This stretch should be a brightness-independent color-preserving asinh stretch, though in practical terms, it seems to work best for optical images.

It may be useful to scale individual channels; sliders allow you to do so. The Q parameter has another slider. For a linear stretch, Q=0; increase Q to change what features are emphasized. Pedestal values can also be set to allow the level assigned to "black" to change.

The number that appears circled in blue over the layers icon tells you at any given time how many layers you have on the currently selected image (the image outlined in brown).

If you click this layers icon, you will get a pop-up window with a list of all the layers you have on top of the image. Here (on the right) is an example of a well-populated layers pop-up; in real life, this is scrollable to see several more layers). From this pop-up, you can: turn layers off and on (click on the switch on the left of the corresponding row); remove layers entirely (click on the 'x' on the right of the corresponding row); change colors of overlays (see below); change symbol shapes and sizes (for overlaid catalogs), including hierarchical catalog settings; change annnotations (for markers); or change units (for the coordinate grid or the distance tool). To add entirely new layers, though, you need to go to other options within the toolbar. You can "show all" or "hide all" with the buttons on the lower left of the pop-up window. To make this pop-up window go away, click on the 'x' in the upper right of the pop-up. Note the target description: This reminds you of the target on which you searched -- here, it was M101, where the coordinates were resolved by NED (as opposed to Simbad). The two icons next in that row indicate, respectively, "copy this location to the clipboard" and "center image on this position."

Finder Chart has slightly more complicated layers -- because the nature of the tool means that it often has results from more than one survey, you have different layers that are shown by default on each survey. Here is an example of a layers pop-up. The active image is a 2MASS image, so the current row is 2MASS. I have the option of turning on the artifacts (glints and persistence), but they're turned off here. The WISE catalog is there in a layer, but not shown on the current row (2MASS). The 2MASS catalog is there, but shown only on the current row (2MASS). My search position is shown on all images. (There are more rows, not shown, corresponding to other surveys.) I can change which catalogs are shown on which images from this pop-up.

Where it's possible to change colors of a layer, click on the 'colors' link to be taken to a new pop-up from which you can select a new color. From here, you can click on your desired color in the top colorful box. Immediately below that box, you can change the color and saturation of the top box so that you can select from a different range of colors. Below that, you can enter numerical hex codes or RGBA values (where the value for RGB is between 0 and 255, and A is in units of percent, e.g., 50 = 50%). Finally, you can also select from a pre-defined set of 15 colors by clicking on any of the small boxes. Note that the numerical codes update as you select different colors. Your choices are implemented as soon as you select them. Click 'Close' to close the window, or click 'x' in the upper right. If you have a catalog loaded into the tool, you can also obtain this pop-up by clicking on the color swatch in the heading of the catalog tab.

For catalogs or the search target, you can also select the symbol shape and size. To adjust the size, type in the symbol size in pixels or use the up/down arrow keys to change the size by one pixel at a time. Your choices are implemented as soon as you select them. Click 'Close' to close the window, or click 'x' in the upper right.

The images window pane consists of rows of images grouped by survey. Near the top of the images window pane, you can find this icon: . If you click on this icon, at the end of each row, a 3-color image appears that has been created out of the bands going into that survey. Here is an example for HL Tau:

At the end of each set of survey images is a new, 3-color image. This image has been automatically generated with pre-selected bands as the color planes:

The "3-color" button is "sticky" in that if you turn it on, and then do another search, the new search will automatically make 3-color images.

⚠ Tips and Troubleshooting:

• To save the color PNGs, you can do either of the following: (1) Click on the image to select it (make it outlined in brown). Go to the image toolbar, click on the tools icon, and find the diskette icon. Select "png" for the file type to save, and click 'save.' (This follows what is described here.) (2) Click on the "prepare download" button in the far upper left of the images window pane. Click on "include PNG color images" in the download options pop-up. (This follows what is described here.)

• -- Extract down through image planes
• -- Extract a line from the image
• -- Extract points from the image

1. Intitiate extraction mode
2. Set aperture
3. Try extraction; repeat if desired
4. Pin (retain) extraction if desired
5. Download (as table or chart) if desired
6. Repeat extraction if desired
7. Click on "end extraction" to finish the process.

Here, we cover the basic approach, with specifics of each tool integrated as we go along.

Intitiate extraction mode. When you click on one of these icons, you enter into the extraction mode. Text appears next to the image toolbar to remind you that you are in this mode: When you are done, to end this mode, click on this "end extraction."

When starting out, the pop-up window that you get depends on the tool you pick.

For the drill:	for the line:	and for the points:

Try extraction. From this point, you can click on your image, or click and drag for the line tool. The pop-up then contains a plot of your extraction.

For the drill:	for the line:	and for the points:

Note that for the line, if you have more than one image loaded and visible, you can shift-click on a new image to see the same line on a new image. Similarly, for the points, you can shift-click to change images without extracting points. For the line extraction, if you want to change at this point to extraction along a line or column, use the drop-down menu at the bottom of the pop-up (shown here as "free hand selection").

Pin extraction. Once you have an extraction that you like, you can retain the extraction for further analysis. "Pin chart/table" extracts the information as a table, just like any of the other tables in this tool, with an accompanying plot. You can then manipulate the table/plot just like any other table or plot in this tool. If the tool recognizes the extraction as a spectrum, you may have additional capabilities.

Once you pin or save your extraction, the tool leaves a "footprint" of your extraction on the image so that you can remember what the extraction was. NOTE THAT it is not interpolating across fractional pixels here. It is averaging if you have asked it to average, but particularly if your pixels are large, if you draw a line that is diagonally across pixels, it will be immediately obvious that it's not interpolating. This line gets rendered as these pixels:

The point appears on the image at the lower left corner of the relevant pixel.

You can pin as many different extractions as you want.

From the line extraction pop-up, when you click on "Pin Chart/Table", you get another pop-up:

From this pop-up, you can choose to do a line extraction from just the currently selected image (most likely where you drew your line); all the images and putting all of the extracted lines into one big table (and tab); or all the images and putting all of the extracted lines into individual tables (and tabs). When you do this, the question naturally arises as to how the tool should specify which column (or tab) goes with which image. Some of the images have long, sometimes cryptic titles. You can choose to have the tool use the full image titles in the column headers or tab titles, or abbreviations.

If you choose to have the tool generate one table for each image you have loaded, you may suddenly have a lot of new tabs at the bottom of the screen. There are navigation aids within the tables section that may help.

Download extraction. You can download the extraction as a table or plot without pinning it. Download as Table saves the table to your local disk -- first, you have the same options as immediately above, where you can choose to do a line extraction from just the currently selected image; all the images and putting all of the extracted lines into one big table; or all the images and putting all of the extracted lines into individual tables. Then you have all the same save options as a regular table. Download Chart saves the plot as shown, as a png file.

After pinning an extraction, you also have the extraction appearing as a table in the tables section of your window and as a plot in the plots section of your window. As with any table in this tool, you can save the table by clicking on the diskette icon in the table. You can choose from a variety of formats; see the tables chapter for more information. Similarly, as with any plot in this tool, you can save the plot by clicking on the diskette icon in the plot. See the plots chapter for more information.

Repeat extraction. As long as the extraction pop-up is still open, you can continue to click points or draw lines to make additional extractions.

End extraction mode. When you are done, to end the extraction, click on "end extraction" to end the extraction. Alternatively, just click on the 'x' in the upper right corner of the extraction pop-up.

Advanced capabilities If you have a complicated multi-extension FITS file with HDUs that are labeled things like image, uncertainty, variance, flags, etc. (which is very unlikely to happen in Finder Chart), you have some additional options for extraction. When you pin the extraction, you can specify an aperture larger than 1x1, which then begs the question of how the pixel values are combined. When you have information that the tool recognizes, and when you choose a larger aperture, you then get an additional pulldown from which you can choose how the pixels are combined: average, sum, or even logical "OR", depending on the data:

First, from the drop-down, you are given a choice of a rectangular selection or an elliptical selection:

When you have selected a region of the image, additional icons appear above the image, and exactly which icons you see is a function of whether or not you have a catalog overlaid: These icons allow you to do several things:

Crop the image

Crop the image to the selected region. Then you can save the cropped FITS image via the save icon described above.

Note that, if you have a rotated FITS image such that a crop would have to bisect pixels, it will show you the region that encompasses your selection. If you crop at that point, then, it will crop in image space (such that pixels are not bisected). See the figure below -- in the original image, north is up. This has been rotated 45 degrees. The selected region is in white. The yellow dash-dot line is the crop in pixel space that encompasses the selected region.

Select sources (and cancel selection)

(Only if a catalog is overlaid) Select the catalog sources overlaid on the image within the region. Selecting highlights the sources in the list and plot with a different color row or symbol. Once there are selections made, the second icon appears to give you an option to cancel the selection.

Filter sources

(Only if a catalog is overlaid) Filter the overlaid catalog down to the sources within the enclosed area. When you choose to impose a filter via this selection mechanism; the filters icon changes above the catalog to indicate that there is a filter applied (). To clear the filters, click on the cancel filters icon (which also appears after you impose filters): . There is much more on filters in the Tables section.

Zoom the image

Zoom the image to fit the selected area into your field of view.

Recenter the image

Recenter the image on the selected area.

Obtain statistics

Obtain statistics from the image on the region. The statistics option results in a pop-up that looks something like this:

Note that it calculates the location of the minimum and maximum fluxes, and the aperture and flux-weighted centroids; the flux values given are in the same units as the FITS file. If you put your mouse over the row of the table in the pop-up, that location appears as an 'x' on the image.

Search

This tool implements a new search, an "action", on the region you have selected. It results in this drop-down (right). where this example is based on a region centered on 210.807785m 54.344223, J2000 decimal degrees, over a 4-cornered polygon. (You can also use the region tool to define a cone; this example happends to be a rectangle.) From this drop-down, you can launch: A TAP polygon search over this region (more information about TAP searches) A NED cone search at this position with a radius attempting to correspond to this polygon (more information about NED searches); results loaded into this tool. A Simbad cone search at this position with a radius attempting to correspond to this polygon; results loaded into this tool. A Simbad cone search at this position with a radius attempting to correspond to this polygon, but launch another browser window or tab at Simbad with the results. A TAP cone search at this position with a radius attempting to correspond to this polygon (more information about TAP searches); results loaded into this tool. Refine the search region.

The last option brings up another pop-up window (similar to this) that allows you to refine the search region iteratively by choosing a cone or polygon, setting the center, and setting the cone size or polygon vertices.

From here, you can change the kind of search, refine the positions, launch searches from your refined position (blue button on lower left), and select from the image again (drop-down on the lower right).

⚠ Tips and Troubleshooting

• The "region selection" tool also appears in the slightly different context of interactive target refinement in several other places in this tool, where it works in a a very similar fashion.

For each of these choices, the markers appear initially in the center of the loaded images. The first mouse click you make in any of the images will move the marker to that location.

Each of these marker choices, when overlaid and/or selected as 'active', has a dot-dash square around it. If it is asymmetrical (most of them are), it has an additional "appendage" and a red plus at the center of the footprint:

These so-called "handles" allow you to resize and/or rotate the marker, depending on the nature of the marker. These handles only appear when the marker is selected as active; if you wait a few seconds, they vanish.

⚠ Tips and Troubleshooting

• Some of these footprints are large. If you have a small image, some of these footprints will be larger than your image. Zoom out to see it, or find a larger image to use. If you overlay, say, a Nancy Grace Roman Space Telescope (formerly WFIRST) footprint on a 2MASS Atlas FITS image, you may need to zoom out a considerable amount before you can see the Roman footprint. You will see the center indicator of the marker before you will see the Roman footprint itself.
• You can add multiple copies of the same marker using the layers pop-up (described generally above). From the layers pop-up, there is a link right under the 'angle' option that says "Add another [marker type]" -- click on that to get an additional marker of the same type. You can also add a label to the marker from the layers pop-up, or change its color.
• If you have many footprints on the same image, you may have trouble grabbing and moving footprints lower in the stack of layers on the image. For example, overlay footprint 1, then footprint 2, and you might have a hard time grabbing and rotating footprint 1 after footprint 2 has been added. The only workaround here is to use the layers pop-up (described generally above) to temporarily hide footprint 2, then move footprint 1, then restore footprint 2.
• If you have images of very different resolutions loaded (e.g., IRAS and really anything else), sometimes it struggles to render the marker on each image. You may need to place markers on one image at a time. (Unclick the "lock color & overlays" option to place markers one image at a time.)

The remaining markers are all footprints from various telescopes: Spitzer, SOFIA, HST, JWST, and Roman. HST, JWST and Roman are derived from information provided via MAST (see http://gsss.stsci.edu/webservices/footprints/help.html .) For Roman in particular, they are pre-launch values.

Spitzer/IRAC 3.6 and 4.5 micron footprints. These two footprints are placed separately from each other. The footprint can be moved or rotated. Click and drag the center of the footprint. A circle appears with four small circles ("handles") around it. Grab and drag the small circles to rotate it, or drag the big circle to move it. Change the color, delete, or add more copies of the IRAC footprints from the layers pop-up.

SOFIA footprints. Several different SOFIA footprints are available; the graphic here shows a selection of them. The available footprints (all of which are placed separately) are:

• FIFI-LS
  • Blue (50-120 microns)
  • Red (110-200 microns)
• FLITECAM
  • Imaging
  • Grism ABBA
  • Grism AB
• FORCAST
  • Imaging
  • Grism a
  • Grism b
• FPI+
• HAWC+
  • 53 microns (Band A), Total Intensity
  • 53 microns (Band A), Polarization
  • 89 microns (Band C), Total Intensity
  • 89 microns (Band C), Polarization
  • 154 microns (Band D), Total Intensity
  • 154 microns (Band D), Polarization
  • 214 microns (Band E), Total Intensity
  • 214 microns (Band E), Polarization

HST footprints. You can overlay the whole focal plane footprint, shown here, or individual instrument footprints (NICMOS, WFPC2, ACS/WFC, ACS/HRC, ACS/SBC, WFC3/UVIS, and WFC3/IR). Consult the HST documentation for specifics on which apertures are which. The footprint can be moved or rotated. Click and drag the center of the footprint. A circle appears with four small circles ("handles") around it. Grab and drag the small circles to rotate it, or drag the big circle to move it. Note that if you overlay the footprint on a very small image, nothing will appear to have happened. You need at least a 45 arcmin image to comfortably see the footprint. Change the color, delete, or add more copies of the HST footprints from the layers pop-up.

JWST footprints. You can overlay the whole focal plane footprint, shown here, or individual instrument footprints (FGS, MIRI, NIRCAM, NIS, and NIRSPEC). Note that if you overlay the footprint on a very small image, nothing will appear to have happened. You need at least a 30 arcmin image to comfortably see the entire JWST focal plane. Please consult the JWST documentation for details about the footprints. In all cases, if the footprint is 'active', a circle near the middle of the footprint will appear with four small circles ("handles") around it. Grab and drag the small circles to rotate it, or drag the big circle to move it. Change the color, delete, or add more copies of the footprints from the layers pop-up.

Nancy Grace Roman Space Telescope focal plane footprint. As above, the footprint can be moved or rotated. Click and drag the boresight (the cross hairs), which appears by default to the upper right of the array of squares. A circle appears, centered on the boresight, with four small circles ("handles") around it. Grab and drag the small circles to rotate it, or drag the big circle to move it. Note that if you overlay the footprint on a very small image, nothing will appear to have happened. You need at least a 60 arcmin image to comfortably see the footprint, and even then you will probably have to click and drag to see the entire footprint. Consult the Roman documentation for specifics on the apertures. Change the color, delete, or add more copies of the Roman footprint from the layers pop-up.

HD 555 is a relatively isolated bright star. If you do a single target search on "HD 555" with everything set as defaults (300 arcsecond images, all images but IRAS, yes search corresponding catalogs, within a 5 arcsecond search radius), it will do exactly as you ask, and return this:

Each catalog has one point at this location, and no other points within 5 arcseconds. So, it looks like the search might have failed, because especially at this scale, all the catalogs have a point at the same location, right on top of the bright star (HD 555) and each other, and no catalog has additional sources that 'stand out' in comparison to that bright star. (And, the plots look super boring too.) Moreover, DSS doesn't have a corresponding catalog, so there are no catalogs on that row of images. If you go to the layers icon (shown in the screen shot above), you can see that all the catalogs that you requested are there. Note, though, that the catalog is overlaid on the corresponding images -- that is, the 2MASS catalog appears on the 2MASS images, the WISE catalog appears on the WISE images, etc. You can change that via the layers pop-up -- you can turn the WISE catalog on for the 2MASS or DSS images, etc. In that fashion, you can, for example, easily see whether the WISE catalog has counterparts to an object seen in the 2MASS images, etc.

HL Tau is a bright binary star. If you do a single target search on "HL Tau" with everything set nearly as defaults (300 arcsecond images, all images but IRAS, yes search corresponding catalogs, within a 35 arcsecond search radius), it will return this:

Now it is much more obvious that the catalogs are returning different sources for each row. SDSS has returned a 'halo' of (apparent) sources here, and both 2MASS and WISE have resolved the binary. Once again, the catalogs are all there, and you can control which catalogs appear on which row via the layers pop-up.

If you search on M101, and this time ask it to return 300 arcsecond images, nearly all images (except IRAS), yes search corresponding catalogs, and now search within the image boundary, you get this:

You can see that Spitzer/SEIP has detected so many sources that the image itself is now difficult to see, whereas 2MASS has detected far fewer sources, and WISE is somewhere in between those two extremes. You can use the layers pop-up to toggle off and temporarily hide the catalog overlay, or change the color/size of the points to make the background image easier to see.

See both the Tables section and the Catalogs section for much more information on tables and catalogs in general.

⚠ Tips and Troubleshooting:

• If you want to overlay a source list on all the images retrieved from a multi-target search, don't overlay it as a regions file; regions files will only be shown on the currently selected target's images. Overlay your source list as another catalog on its own, and then those sources will appear in each image for each target.
• If you leave the layers pop-up window open while you click on different images to select them, you can see the contents of the pop-up layers window change to reflect the layers (and options) present in that selected image.
• If you can't figure out whether or not an object that you can see by eye in, say, 2MASS, has been detected by WISE, click on a 2MASS image, go click on the layers icon to bring up the layers pop-up window, and turn on the WISE catalog for the 2MASS images. Then you can easily see (modulo any proper motion) whether or not WISE detected the 2MASS source.
• If you can't really see the image through the sources from a given catalog, but you still want to see the points from the catalog, go click on the layers icon to bring up the layers pop-up window, and change the size/shape of the points to make them less prominent.