and HiPS
formats. Any catalogs you have loaded are
overlaid on the images; see visualization
chapter for more information.
Contents of page/chapter:
+Searching for and Loading Images
+Making 3-color Images
+HiPS Images: General Information
+Searching for HiPS Images
+Adding New Images
+Coverage Image
+Automatic FITS-HiPS-Aitoff Transitions
If the first screen you come to is an empty results page, then you
need to decide what to load. To search for images, click on "images"
at the top to begin an image search:
If you do not have an image pre-loaded, the default start position is
in the position search for images. It is assuming by default that you
want to load a FITS image from IRSA services, though you can also load
a FITS image from disk or off another service on the web (see below).
(Flexible
image transport system, FITS , files are widely used in astronomy and are an easy
way to store images.)
The search window looks like this:
(more on HiPS below; also see IVOA docs
for more about what HiPS
images are).
("Workspace"). Note that to use
the Workspace (reading from or writing to it), you'll need to log in. In the cases other than "Search", nearly all of the additional options below this line vanish because they are no longer relevant. To select an image off of your local disk, select "Use my image", and then tell it where to find the image on your local disk. To load an image from the web, pick the "URL" option and enter the URL from which you want an image loaded. To load an image from the IRSA Workspace, pick the "Workspace" option and find the file you want to load.
If you would like to load an image from IRSA's archives, select "Search" and go on to these subsequent additional search parameters.
As you are completing a valid coordinate entry, it echoes back to you what it thinks you are entering. Look just below the box in which you are typing the coordinates to see it dynamically change.
Below the box where you enter the target, you can then specify the size of the images you want. You may enter the cutout size in arcseconds, arcminutes, or degrees; just change the drop-down option accordingly.
⚠ Tips and Troubleshooting
On the left hand side, you can filter by :
To expand or contract the options below each of these broad
categories, click on the black arrow on the right. To see all of the
choices in each of these broad categories, click on the black arrow
and then click "more" near the bottom of the list (after which you can
click "less" to collapse it again). In this example, "Mission" is
collapsed, "Project Type" is expanded, and "Band" is fully extended to
reveal more options than are shown by default:
To select any of the options, click on the checkbox on the left. In
response to your selections, two things happen. (1) checked items
appear in highlights above this part of the page, next to "Filter By";
(2) the list of programs for selection on the right hand side changes.
Here is an example where the list has been filtered down to just
include WISE data:
On the right hand side, you can select individual surveys and
individual bands therein. To expand or contract the options below each
of the categories, click on the black arrow on the right, next to the
data set name. To select any of the waveband options, click on the
checkbox on the left of the individual survey or individual bands.
Here is an example showing all of the WISE/AllWISE data selected (via
the tickbox next to "WISE AllWISE"), and just W2 from WISE/AllSky
selected (via the tickbox next to "W2" in the expanded section under
"WISE AllSky"). Note the "Selection" indication at the top.
To find out more information about any given data set, click on the i
in the circle 
. This takes you to a master
list of all data sets available in IRSA Viewer, from which you can
obtain standard information about the data sets (mission, wavelengths,
links to more information about the program or delivery, and more).
If you clear filters on the
left side, it doesn't affect selections you've already made on the
right. You must actually clear all the selections on the right to
reset everything. The most efficient way to do this is by clicking the
'x' next to the selection summary at the top of this portion of the
window -- the 'x' at the end of the "Filter By" line clears the
filters on the left, and the 'x' at the end of the "Selection" line
clears the selections.
If you want to expand all the
choices on the right (to ease in band selection), click on the sets of
arrows in the upper right of this part of the screen to show all
options, or collapse them again.
.
(this accesses a
tool called Data Discovery).
)
and explore the data there. Depending on the data, you may be able to
wander through directories, download them all at once in a tarball, or
search by position.
. Note that as of this writing,
not all of our data are yet available in this tool.
Example of going outside of IRSA Viewer: I want data
covering M16. M16, the Eagle Nebula, is essentially in the galactic
plane. Thus, I don't need to search really any of the extragalactic
data sets. I select on the left hand side, under project type,
compilation, galactic, and all-sky. I am still left with a long list
of programs, though it is much shorter than it was before. However, I
can omit some programs from consideration based on their names --
programs studying Taurus or Orion are unlikely to have any data on
M16. I can then individually select the dozen or so data sets likely
to cover M16. I explore the images and decide that the Spitzer images
from the GLIMPSE project are what I would like to explore in more
detail. I can then navigate to the GLIMPSE page , read the documentation to find that they provided
mosaics with two different pixel sizes, and click on the "DCE" link at
the top of that page. I can search by position there to obtain the
mosaics with different pixel sizes.
By default, you can select the red plane first; you then populate that color plane with all the same choices as you would have for a single channel image (as above). To set the additional color planes, click on "green" and then "blue" to populate those planes accordingly.
It assumes that you must want the same position for all three color planes.
Select your options individually for each color plane (red, green, blue), and click 'Search' in the lower left. To exit the search window (i.e., cancel) without creating a new 3-color image, click on any other tab at the top, e.g., "Results" returns you to the results you have already loaded into the tool.
To change the color stretch of each color plane individually, click on the "Color Stretch" icon in the toolbox on the top of the images pane; see the Visualization section. Much more detail about interacting with images can be found in the Visualization section.
⚠ Tips and Troubleshooting
stands for hierarchical progressive surveys, and these kinds of images
are multi-resolution HEALPix
images (where HEALPix stands for Hierarchical Equal Area isoLatitude
Pixelation). (Also see IVOA docs on HiPS .) In practice, what this means is that you can
interact with images of a very large chunk of sky, and as you zoom,
the pixel size changes dynamically. HiPS images are fundamentally
different than FITS images, and as such, what you can do with the HiPS
images are different than what you can do with the FITS images. The whole point of HiPS images is to provide on-demand resolution changes. Zoom out, and it loads large pixels. Zoom in, and it loads smaller pixels. HiPS images are designed to cover large areas of sky efficiently. If you need to visualize many degrees, this is the image type to use.
There are HiPS images from all over the world available via the web;
the complete list of HiPS images available from the images search
page includes (once the "IRSA Featured" checkbox is unchecked) many
HiPS images from CDS .
HiPS images typically have the color and stretch set by the person who originally made them. The color table can be remapped within this tool. But, you cannot, in general, change the stretch of HiPS images with as much flexibility as you can with FITS images. This is why there may be multiple versions of some data sets in the list of HiPS images.
HiPS maps typically come with a Multi-Order Coverage map
(MOC). A MOC is a
format developed by the International Virtual Observatory Alliance to
specify sky regions. In this context, a MOC tells you via a simple
boolean yes/no, is there sky coverage from this data set in this
region. You can overlay a MOC from one data set onto a completely
different data set's HiPS image.
Note that here, in the context of HiPS images, the field of view (FOV) here has different limits than FITS images; it can be no smaller than 0.0025 deg, and can be up to 180 degrees. If you leave this blank, it will simply load the entire HiPS image for you.
) to
pick from. Column definitions. The table that appears when selecting a HiPS image has several columns:
in the second column of the table. Another
window will spawn with basic information about that HiPS image.
You can use the same target as before, or change the target. To exit the search window (i.e., cancel) without getting a new image, click on any other tab at the top, e.g., "Results" returns you to the results you have already loaded into the tool.
⚠ Tips and Troubleshooting
After you have done an initial
search on a set of images, when you go back to the Images tab,
those same images are still selected. If you just click
'search' again, you'll get a second copy of all of the images you
initially selected. You must actually clear all the selections on the
right to reset everything. The most efficient way to do this is by
clicking the 'x' next to the selection summary at the top of this
portion of the window -- the 'x' at the end of the "Filter By" line
clears the filters on the left, and the 'x' at the end of the
"Selection" line clears the selections.
| You may have a coverage image like this -- this is an example
of a coverage image showing two different overlaid catalogs. Note that in this case, the catalogs cover the whole sky, so the HiPS image is displayed in HiPS/Aitoff projection to show the whole sky. |  |
| You can also have a coverage image like this, which shows a coverage image that has polygons demonstrating the coverage of each a list of loaded images (large polygons) and the locations of spectra (small squares). This case only has data over a relatively small region, so the HiPS image is zoomed in comparatively tightly on the relevant region. |  |
In all cases, you can interact with the coverage image in pretty much exactly the same way as you would any other image loaded into this tool; see the the visualization chapter for much more about those tools.
The thing that makes a coverage image a little bit different, however, is that it can automatically adapt. The next subsection covers more details about how it automatically changes to accomodate your needs and zoom level.
Note that if you swap between HiPS and FITS and back again, it
will include a region on the HiPS image that is the footprint of the
FITS images you had just loaded. A label appears at the center of that
footprint, which may be disconcerting if you are not zoomed out enough
to see the region itself. Here is an example, zoomed out so it is
clear what is going on:
adds a layer that
indicates where there are (or are not) data.