Chapter 8.           Visualization

8.1   Visualizing data in the Spitzer Heritage Archive

Powerful visualization tools were important to the original Spitzer observation planning and archive tools (Spot and Leopard), and the descendents of these tools are included in the SHA. These tools can be used to understand exactly what each observation did and in deciding what data to download.

 

FITS images from Spitzer or other bands (or from your computer) can be loaded into the viewer. If performing an SHA search, the footprint of the observation can be overlaid on an image of your choice. Individual data products can be viewed interactively and flux density levels assessed.

 

The viewer within the SHA itself can be found in two places. Clicking on "Read FITS File" on the top set of blue tabs allows you to load a FITS file from disk or from a variety of online sources, resulting in a visualization-only panel. Alternatively, and perhaps more frequently encountered, once a search is completed, several of the tabs in the Details pane on the right result in a visualization window so that you can examine the data interactively. Please see the chapter above on the details pane for complete information, but in summary, there is one tab entitled "Details" that has text, and the rest have various representations of the data.

8.2   FITS Viewer

All of the interactive image visualization tools work the same basic way, and here we describe these basic options, in basically the order in which they appear in the window, from top to bottom, left to right.

 

Interactive exploration of the image with the mouse

Move your mouse over any image that is loaded into the FITS viewer. A pop-up window appears in the upper right 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. This popup window automatically appears when your mouse is over the window; if you want to make it 'stick', click on the lock icon.

 

Finding more about the displayed image.

The top of the display (just under the tab headings) gives a title of the image. This abbreviation may be a little cryptic. ISSA or IRIS are both IRAS data. IRAC and MIPS are self-explanatory. 2MASS comes up by default to be used for small fields of view, and as such, the Spitzer fields of view may be off the edge; this will be fixed in a later release.

Expanding the image.

Clicking on this icon will enlarge the visualization window into a window that takes up the whole browser window. This also enables you to look at more than one visualization window at a time.

 

More about the expanded view.

Depending on what you've just been looking at, this expanded view may give you choices of multiple panes. Just to the right of the "Collapse" button in the upper right, you have these choices:   The leftmost one shows one image at a time, the center one tiles all the available images, and the rightmost one results in a pop-up window allowing you to choose which plot to display. If you choose to display one image at a time, the top of the frame changes to something like this:

which allows you (via the blue/green buttons) to scroll through your list of images (only two images here), with an indication of which image you are currently inspecting (a Level 2 product footprint here, overlaid in an IRAS image).

 Image options.

There are a variety of display options that can be configured once you click on the image options icon. If you do that, you get a popup window at the top of your browser:

from which you can select a variety of options, now described.

 

Saving the FITS file.

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

 

Note that, as of this version, whether you save FITS or PNG, what is saved will not include any overlays or annotations you may have placed on the image. Saved FITS images will not save the color stretches.

Zooming in or out.

Clicking on these magnifying glass icons zooms you in or out of the image. The readout of how many times you are zoomed appears at the top of the visualization window. To return to a zoom corresponding to the original size, click on the magnifying glass with a 1 enclosed. Note that there is a maximum zoom allowed -- 64 times. To enlarge things more than that, please select another background image, one of smaller spatial extent.

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.

Changing the background image.

By default, the SHA tries to pick a good background image, but you may wish to try another wavelength or field of view. By clicking on this icon, you bring up a pop-up window. The first part of this window shows the central RA/Dec that you are about to request (you can change this by clicking on "Modify Target" and all the usual options appear). The next part of this window has a series of tabs: IRAS (12, 25, 60, and 100 microns), 2MASS (J, H, and Ks bands, or 1.25, 1.65, and 2.17 microns), MSX (8.28, 12.13, 14.65, and 21.3 microns), DSS (the usual red/blue plates and a variety of scan options), a FITS file from your local disk, or a URL that you can enter so the browser can retrieve a FITS file from the web. From this pop-up, you can also choose to create a 3-color image, loading a new FITS file separately for each color plane. Note that this 3-color option only appears for background images, not Spitzer data, unless you have loaded Spitzer data from disk..

Locking or changing the background image

You can lock the background image or change it to be something else by clicking on this image.

Changing the color table.

Click on the colorful icon to change the color table of the background image. A wide variety of color table choices appear when you click the button, and you can select your new color table.

Changing the color table stretch.

Click on this icon to change the specific stretch of the color table to be one of several pre-defined standard options. The options appear in a pulldown when you click the button.

Customizing the color table stretch.

Click on this icon to customize the specific stretch of the color table. A pop-up window appears with a histogram of the colors, and you can interactively change and customize the stretch of the data as displayed.

Viewing the FITS header.

This icon will display a pop-up window with the FITS header of the background image. You can use this option to view the FITS header of a Spitzer data product via the Data tab.

Adding a coordinate grid.

Click on this icon to overlay a coordinate grid on the image. Click it again to remove it.

Selecting a region.

When you click this icon, at first, nothing seems to happen. However, you can now click and drag in the image, selecting a box on the image. Grabbing and dragging the corners of the box can resize it. When you have selected a region of the image, additional icons appear above the image. These icons will allow you to crop the image to the selected region () or obtain statistics on the region ().

Rotating the image.

This feature allows you to rotate image to any angle of your choice, in degrees. It will rotate the image counter-clockwise (to the left) from the original image, not the current view.

Rotating the image so that North is up.

Images that you download from IRAS or DSS or 2MASS commonly are already oriented such that North is up. However, when interactively investigating Spitzer products, North is not necessarily up. The Spitzer images and mosaics are constructed to optimize the resultant size of the mosaic. However, when interactively investigating the image, it may be helpful to orient North up, and this clicking this icon performs that function.

Measuring a distance.

When you click this icon, at first, nothing seems to happen. However, you can now "draw" a line on the image, and the length of the line is displayed.

Recentering the image

This button recenters the image in your window, e.g., it puts the center of the image in the center of your window.

Viewing/changing the order of 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. 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. Here you can change what is displayed and what colors get used for it.

Getting help.

Clicking on this icon takes you to the context-sensitive help page.

 

There is additional information on retrieving and using catalogs above/below.

 

8.3   Spectrum (X-Y Plot) Viewer

Some of the data products associated with spectroscopy are images (e.g., the original images that were read out from the instrument), but reduced spectra can be viewed from any results tab (except for the AOR tab). These files appear as a "Table" in the "File Type" column of the results table. Select one of them in the results pane, and then look at the "Data" tab from the details pane, and you will be able to interactively explore the spectrum. Move your mouse along the spectrum, and a popup display shows you the corresponding wavelengths and flux densities. If you are getting no pop-up display, click once in the window to be sure your computer knows you are there.

 

(This visualization tool can be used with any x-y plot, but in most SHA cases, it's used for viewing a spectrum.)

 

Finding out more about the displayed spectrum.

The top of the display (just under the tab headings) gives an indication of the observation and what is plotted.

Expanding the spectrum.

Clicking on this icon will enlarge the visualization window into a window that takes up the whole browser window. This also enables you to look at more than one visualization window at a time.

More about the expanded view.

Just as for the image view, depending on what you've just been looking at, this expanded view may give you choices of multiple panes. Just to the right of the "Collapse" button in the upper right, you have these choices:   The leftmost one shows one image at a time, the center one tiles all the available images, and the rightmost one results in a pop-up window allowing you to choose which plot to display. If you choose to display one image at a time, the top of the frame changes to something like this:

which allows you (via the blue/green buttons) to scroll through your list of images (only two images here), with an indication of which image you are currently inspecting (a Level 2 product footprint here, overlaid in an IRAS image).

 

Importantly, though, for the IRS enhanced products, some options are only available in the expanded view. In the expended view, you can turn on/off plotting of various orders and synthetic photometry points.

Zooming in or out.

Unlike an image zoom, here you have something called "Rubber band zoom." Use your mouse to denote a region by clicking-and-dragging from the upper left to the lower right of the region on which you'd like to zoom. This region is then expanded in the viewer. To return to the original view, there is a link at the bottom of the viewer that says "Zoom out to original chart" which returns you to the default view.

"Chart Options"

For the spectrum visualizations, a "chart options" link is available in the lower left. This brings up a pop-up window entitled "XY Plot Options" with various configurable options to further manipulate your plot.

 

In the pop-up, you have these options:

·    Plot Error -- add the errors to the plot. They appear as a light grey 'envelope' around the spectrum.

·    Plot Synthetic Photometry -- checked by default, this overplots the synthetic photometry that is part of the IRS enhanced product. If you are not viewing an IRS enhanced product spectrum, this option does not appear.

·    Plot Style -- change how data are presented on the plot. The options are "Connected Points", "Unconnected Points", and "Line". Connected points shows the individual points and a line connecting them. Unconnected points shows just the individual points. Line shows just the line connecting the points.

·    X min/X max and Y min/Y Max -- manually change the range of the plot. You can also 'rubber band zoom', as per the above. Please note that unlike zoom, changing the range drops out-of-bound points, and some points that were not adjacent before might become connected as adjacent.

·    X Column and Y Column -- change what is being plotted. Click on the blue circled "i" to get a list of the choices.

 

"Restore Default" undoes any changes you made, and "Apply" implements any changes you made.

 

Note that if you change what is plotted on the Y axis, the ability to overplot errors and synthetic photometry goes away.

 

These options are preserved through the current search. It will be reset to the defaults in the next search, or when the search is redone.

 

If the plot ever looks strange, go back and make sure that you have clicked 'Restore Default' in this pop-up. This always applies to the current plot.

"Download Data Table"

For all spectrum visualizations, a "download data table" link is available in the lower right. This will allow you to save the source data table which is being plotted..

Saving a particular view

The best way to save a particular view of a particular spectrum/zoom/annotation/etc. is to do a screen snapshot. The specifics for this vary according to your platform and OS version.