PTF Image Service: Visualization

Visualization Overview

You can overlay catalogs and add other layers to your image (such as 2MASS glint artifacts). Click on the blue "Catalogs" tab near the top of the page to initiate this process. See the catalogs section for more on catalogs, including how to make plots.

Note that the sky coverage of the displayed images overlaid on an IRAS 100 um map is shown under the 'coverage' tab.

Note that all the images that are displayed are FITS files, not JPGs or PNGs, so you can interact with them using the tools described below.

Basic FITS Viewer

Interactive exploration of the image with the mouse.

Move your mouse over any image that is loaded into the viewer. Details about the image and, specifically, the pixel beneath your mouse cursor, appear along the top of the window with a variety of useful items. Some information is updated in real time (such as coordinates); some information (such as flux densities) is updated when you stop moving your mouse for a second or two. The image can be interactively investigated in this fashion.

You can make it 'stick' on a particular place on the image -- tick the "Lock by click" box and then click on the image at your desired location.

The orientation of the image is given with a compass rose on the right, next to a zoomed-in view of the image under your cursor. If you can't see all of these two windows, enlarge your browser window slightly.

Finding out more about the displayed image.

The results are grouped by survey. It indicates the survey origin and the date of observation (instrument, channel, and date in black, on the top of each image).

Some of this information (like the title of the image) is also given in the interactive exploration region described immediately above. This region also includes additional information about the image (such as the pixel scale and orientation).

Visualization Tools -- Image Options

Saving the image.

The diskette icon will allow you to save the current image as a FITS or PNG or Regions file to your local disk. 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.

Saved FITS images will not save the color stretches or overlays; it will just save the underlying FITS image. Saved PNG files WILL include 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 the FITS file; see the select region icon below to crop, and then save the FITS image.

Note also that if you overlay a catalog consisting of tens of thousands of sources, to save bandwidth, what is overlaid on your image at some locations may be a larger symbol representative of several sources at that location; if you save a regions file from the catalog overlay, then you will have fewer sources in the regions file than you have in the full catalog.

Zooming in or out.

Clicking on these magnifying glass icons zooms in or out of the image. The readout of how many times you are zoomed appears at the top of the visualization window.

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

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 things more than that, please repeat your search to obtain new images with smaller (or larger) spatial extent.

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.

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. 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.

Changing the color table.

This icon enables you to change the color table of the displayed image. When you click the button, a drop-down menu appears with a wide variety of color table choices. Select your new color table from the options shown:

Changing the color table stretch.

This icon enables you to change the color table stretch of the displayed image. When you click the button, a drop-down menu appears with a variety of choices. You can choose from a set of pre-selected options:

If you pick the first one, "color stretch", you can customize the stretch. A pop-up window appears with a histogram of the values in the image, and you can change the stretch type and range.

If you pick a color stretch from the pre-defined options, the pop-up window reflects this change. (Ex: pick 'Linear stretch to 99%'. Go back to "color stretch". 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.)

Rotating the image to any angle

This feature allows you to rotate the image to any angle of your choice, in degrees. It will rotate the image counter-clockwise (to the left) from the current view, not necessarily the original image. For example, entering "45" in the rotation pop-up and hitting "rotate" will rotate the image 45 degrees counter-clockwise relative to its original orientation. Then selecting the icon again, and entering "180" in the pop-up (followed by hitting "rotate") will rotate the image an additional 180 degrees counter-clockwise. To exit the pop-up without making further changes, hit the blue 'x' in the upper right of the pop-up.

Rotating the image so that North is up.

Images retrieved from FinderChart are commonly already oriented such that North is up, or close to it. However, when interactively investigating images, or in certain situations, 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.

Re-center the image.

Clicking this icon will re-center the image on the center of the last query, or on the center of the image.

Selecting a region.

When you click this icon, at first, nothing seems to happen. (There is a notice with brief instructions that appears on the lower left of your browser window.) You can now click and drag in the image, selecting a box on the image. This box can be resized by grabbing and dragging the corners of the box. You can make a new box right away by holding down the shift key and clicking and dragging to select a new box. When you have selected a region of the image, additional icons appear above the image: These icons will allow you to (from left to right) crop the image to the selected region, obtain statistics on the region, select the catalog sources overlaid on the image within the region, or filter the overlaid catalog down to the enclosed sources. (The last two options will only appear if you have a catalog overlaid.) You can save the cropped FITS image via the save icon (described above). The statistics option results in a pop-up that looks something like this:

Selecting sources highlights them in the catalog list. When you impose a filter, the filters icon changes above the catalog to indicate that there is a filter applied (in this case just one filter: ). To clear the filters, click on the cancel filters icon (which also appears after you impose filters): .

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.

Put a marker on the image.

When you click this icon, you can now mark a position in the image. A red circle appears that can be resized and dragged (or click to move it) to any location in the image. You can change the color of the marker (and add a label to it) via the "layers" icon (described below).

Show the directions of North and East

When you click this icon, arrows appear on the image showing which direction is North and which is East.

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).

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 blue 'x' in the upper right of the pop-up.

Viewing/changing the layers on the image.

If you've been following along by trying these various options, you now have an image with a lot of annotations on it. The number that appears in blue over the layers icon tells you at any given time how many layers you have on the currently selected image. If you click this icon, you will get a pop-up window with a list of all the layers you have on top of the image. From the pop-up, you can turn layers off and on, at minimum, but you can often also change exactly what is displayed and what colors get used for it. To add new things, though, you need to go to other options within the toolbar. Here is an example of a well-populated layers pop-up.

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. To delete a layer, click on 'delete'. Some layers appear do not have that option; to remove that layer, click on the corresponding icon from which you added that feature. To make this pop-up window go away, click on the blue 'x' in the upper right of the pop-up.

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 described above.

Viewing the FITS header.

This icon will display a pop-up window with the FITS header of the background image. If you click on the columns of the FITS header 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. Here is an example of a sorted FITS header. Note that the first column is the original order of the keywords. To make it go away, click on the blue 'x' in the upper right of the pop-up.

Getting help.

Clicking on this icon takes you to this help page.

Select a new image.

Clicking on this icon allows you to select a background image from a variety of surveys, e.g. 2MASS, DSS, etc.

The large "Close" arrow at the left enables you to return back to the pane view. This arrow is always available in these expanded views.

Next, the currently displayed band (sometimes using abbreviations) and magnification factor is shown. Zoom in or out using the visualization toolbox described above.

Next, there is a cluster of icons 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, but still take up the whole browser window with the set" (as opposed to going back to the window panes). Depending on what you have been doing in your session to this point, you may have more than one image loaded, plus a plot from the catalog. Perhaps you wish to see, e.g., just two of the images tiled? Click on the last, blue "list" icon in this cluster to bring up a pop-up window:

This popup window lists all of the images you have loaded, and if you uncheck the corresponding box, that image, while it is still loaded, will not be shown if you, say, scroll through the images, or look at them in tiled mode.

If you do have more than one image loaded, you may also have, on the top right of the image, a set of arrows, labels, and green/blue dots (which only appear when you are viewing one image at a time and have more than one image loaded).

These allow you to navigate through your set of images. The green dot inamongst the blue dots indicates where you are in the sequence of images, and the arrows and labels indicate which image is before or after the currently viewed image. Click on the arrows or the dots to move around in the sequence.