Web Interface Guide
This document describes the use of each of the fields on the
SkyView Web forms. When using SkyView you should be able to
click on the field label to go directly to the relevant portion
of the document. Only the Coordinates/target field and the survey
are mandatory. All others are optional.
The SkyView web interface is an on-line portal to SkyView-in-a-Jar, a Java implementation
of the SkyView geometry engine. The fields on the web form
correspond to settings used there. Detailed information
on these parameters, parameter values, and algorithms is given
User's Guide. Where appropriate the corresponding SkyView-in-a-Jar setting is indicated here.
This document also provides a quick overview on the results page generated from the Query Form
Overall Organization of the Query Form
The standard SkyView form
can be used for all requests. It
aren't being used. A static version
of this page is available
When the standard form first appears many options are hidden. You can
reveal options by clicking on the arrow
links in the page. The will turn into
and a set of options will be displayed.
You can click on to hide the options,
but any changes you have made will be saved.
Submit and Reset
- Pressing this button submits the request to be processed by
SkyView. You can also submit requests by entering
a carriage-return in any text input field.
- Pressing this button restores all fields to default values, clears
survey selections and in general returns the form to the state which
it had when the you first entered it.
When "Display results in new window" is checked, results
will be shown in a window with the target name of "newwin" rather
than the current window. I.e., only one new window will be opened
regardless of the number of requests you make. This option is not available in
Coordinates or Name
- SkyView-in-a-Jar setting: Position
- This field is used to determine the center of the field to be retrieved.
If you specify coordinates these are used as the center.
When equatorial coordinates are being used the RA may
be specified as either hh mm ss or ddd.fff,
i.e., in hours or in decimal degrees. The coordinate fields
may need to be separated by a comma or sign of the declination, but
many coordinate formats will be accepted.
- Usually if any letter is used in this field the field is assumed to be an
object name and is sent to the SIMBAD or NED name resolver to be converted
6 45 10.76 -16 41 57.82
6 45 10.76, -16 41 57.82
- SkyView-in-a-Jar setting: Survey
- These selection boxes allows you to select data from one or more
surveys. You can select multiple surveys either by dragging the
mouse down the box with the button pressed, or pressing the
control-key simultaneously with the mouse button when adding new
selections (note: some browsers behave differently with mulitple
selects). The surveys are described in detail in the
- The surveys are divided according to wavelength regime and any
number of surveys in any number of the different regimes may
be selected. Note that when you click on a survey in one
wavelength regime box you will not de-select any survey that
has been selected in another regime. Typically you can
use <cntrl>-Click to deselect an entry.
Click on the arrow next to "3-D Image Surveys" to show the 3-D surveys options.
A 3-D survey has a vector of values for each pixel location, typically
giving the intensity as a function of energy at that location.
Data may be resampled in both energy and location.
The output image may have a single plane -- a simple scalar image --
or have more or fewer planes than the original data. Data is resampled
in the third dimension assuming that the intensity is constant
throughout a given energy bin. A given output plane is the
sum of the values of each input plane weighted according to the
fraction of the input plane included in the output.
Offset, bin size and number of bins for 3-D surveys
- SkyView-in-a-Jar setting: Ebins
- The offset gives the 0-based offset of the start of the first bin
the user wishes. The bin size gives the number of input bins to
be placed in each ouput bin. The number of bins gives the
number of output bins to be generated for a 3-D survey.
E.g., if the survey has 10 input bins (e.g., EGRET), and the user
wishes to compress all of this data into 3 output energy bins, the
numbers could be 0,3.33333,3. The 10 input bins will be sampled
into three output bins. If we just wanted to compress by a factor
of two and drop the first and last bins, then 1,2,4 would be appropriate.
Fields in Commonly Used Parameters
Click on the Arrow next to "Commonly Used Parameters" to see these
fields. All of these parameters are optional.
- SkyView-in-a-Jar setting: Coordinates
- Click on this field to choose among common equatorial, galactic and ecliptic
coordinates, or enter a special coordinate in the entry box if you
want a less commonly used system. See the
user's guide for details on the supported coordinate systems and their names.
- SkyView-in-a-Jar setting: Projection
- Click on this field to choose among the map projections:
Gnomonic (Tan) -- good for small regions.
Rectangular (Car) -- simplest projection.
Aitoff (Ait) -- Hammer-Aitoff, equal area projection good
for all sky maps.
Orthographic (Sin) -- Projection often used in interferometry.
Zenith Equal Area (Zea) -- equal area, azimuthal projection.
COBE Spherical Cube (Csc) -- Used in COBE data.
Arc -- Similar to Zea but not equal-area.
Image size (pixels)
- SkyView-in-a-Jar setting: Pixels
- You may select the pixel dimensions of the image to be produced. A
scalar value or a pair of values separated by comma may be given.
If the value is a scalar the number of width and height (in pixels)
of the image will be the same. By default a 300x300 image is produced.
Note that pixels need not be square.
Image Size (degrees)
- SkyView-in-a-Jar setting: Size
- This field sets the size of the image in degrees. A single value
or a pair of values separated by comma may be given. If a single value
is given the angular size will be the same in both width and height.
- Note that the default size for an image is the number of pixels times the internal
pixel size of an image.
- Previous versions of SkyView did not support non-square
pixels so that only a scalar value of size was supported and this
always referred to the width or height of the image, whichever was
larger in pixels. Now if when a scalar value is supplied, the
assumption is that the angular dimension is the same in both
height and width, and if the number of pixels are not the same in
the two directions, the pixels will not be square.
Image pixel format
- SkyView-in-a-Jar setting: Float
- By default the FITS files will be produced with
4-byte real numbers. Unchecking on this box will change this to 8-bytes.
Note that all internal calculations are done in 8-byte reals,
and the data is converted at the end to 4-bytes, so that
unsetting this flag may actually reduce the memory used in
a request -- but will double the size of the FITS file produced.
Other Optional Parameters
These options are a little less frequently used. Clock on the
arrow next to "Other Optional Parameters" to reveal them.
- SkyView-in-a-Jar setting: Scaling
- This field selects the transformation between pixel intensity and
intensity on the displayed image. The default logarithmic scaling
generally works well over the entire image. Linear scaling tends
to enhance bright features. Sqrt scaling is intermediate
between the first two and is close to the response of the eye.
Histogram equalization scaling
can sometimes show subtle features in the data. LogLog scaling works nicely with
some surveys that have very large dynamic ranges.
- SkyView-in-a-Jar setting: Sampler
- Once SkyView has retrieved the data requested, it needs to be
resampled so that it can be displayed. SkyView offers several ways
to do this. The default ,
is the nearest neighbor approach, but linear interpolation, a flux conserving,
exact-area, clipping resampling, and higher order Lanczos and Spline
used to determine if the Clip resampler will adjust values according
to the area of the output pixels as appropriate if the survey data uses
intensive measurements (e.g., flux).
- SkyView-in-a-Jar setting: Rotation
- This gives the rotation of the image in the projection plane.
- SkyView-in-a-Jar setting: Resolver
- The name resolver box allows you to choose a name resolver to use
when looking up a name entered in the coordinate/source box (as
opposed to a numeric coordinate value). The default choice is to call the SIMBAD
name resolver first and then the NED name resolver if the SIMBAD
- SkyView-in-a-Jar setting: Deedger
- When multiple input images with different backgrounds
are resampled the edges between the images may be apparent
because of the background shift. This field allows the user
to attempt to minimize these edges by applying a de-edging
algorithm. The user can elect to choose the default given
for that survey, to turn de-edging off, or to use the default
- SkyView-in-a-Jar settings: Smooth
- You can choose to do a boxcar smoothing of the image prior to the image
display. The size of the boxcar in pixels should be entered here.
The boxcar need not be square so a pair of values separated by
commas may be given.
If the value is less than or equal to one then no smoothing is done.
Since boxcar smoothing works only with odd values, an entered even
number will have a one added to it.
- SkyView-in-a-Jar setting: LUT
- Choose from the color table selections to display the data in false
- You may invert the color table by checking the "Use inverse" box.
These options let you draw information on top of the images.
Click on the arrow next to "Optional Overlays" to reveal them.
- SkyView-in-a-Jar setting: PlotColor
- The color of the plot overlays can be changed by entering the name
of a color in this field.
- SkyView-in-a-Jar setting: Min
This box suppresses the display of the underlying images and only
shows the various overlays. It works by setting image minimum to a value
larger than any conceivable pixel value which has the effect
of suppressing the image.
Image Center Reticule
- Check the 'Image Center Reticule' box to draw a reticule positioned at the center of the image
- SkyView-in-a-Jar settings: Grid, GridLabels
- Checking the 'Display Grid' box will overlay
a coordinate grid on the image.
- Check the 'Display Labels' box to annotate the grid with
- By default the grid will be in the coordinate system used
in the image, but you can override that in the 'Grid Coordinates' selection.
- SkyView-in-a-Jar settings: RGB, RGBSmooth
- You can generate true color images by selecting an image for each
version you will need to check that you want an RGB image. If surveys
are selected in both the standard survey area at the top of the form
and in the RGB area, the results may be unexpected.
- A square box-car smoothing can be applied to each image
before combining the three colors. The smoothing should
be given as a trio of values, for the R, G and B planes of
the image respectively.
- SkyView-in-a-Jar settings: Catalog, CatalogIDs, CatalogFilter, CatalogRadius
- The catalog overlays box allows you to ask that the positions of
catalog objects be marked on the image. A listing of all objects
found with their position will be generated. Multiple catalogs may
You can select HEASARC catalogs from the table provided, or select Vizier catalogs
using the input field. Any Cone Search URL may also be entered there.
- The 'Display ID Strings' checkbox controls whether the IDs of the returned
catalog elements will be shown.
- Catalog entries can be filtered using a 'Catalog filter'. E.g., if the
table has a 'vmag' field, then vmag<10 will select out the brightest objects.
- A catalog radius field may be used to select objects only in some region
- SkyView-in-a-Jar setting: Contour,ContourSmooth
- You can choose to display the contours of an image over using this
option. More than one image can be contoured, but the contours of
different images are not distinguished and the scaling options if specified
apply to all.
- The spacing of the contours is controlled by the 'Contour Scaling' options,
and you can also set the minimum and maximum contour levels as well as
- The image can be smoothed by a boxcar smoother before being
the contours are drawn.
SkyView Query Form Results Page
This page displays images generated from the SkyView Query Form.
Each survey will start with the survey title.
A quicklook rendering
of the generated image is shown. If you mouse within this image, the coordinates associated with the pixel
at the mouse location will be shown (for most projections). You can click to freeze this value.
A Zoom link will send a new image request at twice the resolution centered at the last pixel
Links to the FITS and quicklook images are available to support data downloads.
Below these links, some of the criteria used to generate each image are listed along with some information
about the survey. More survey information can be found by following the More Information link which will show our
full survey description.
SkyView Image Gallery
For typical image sizes users will have an Add to Gallery button next to the data links. If clicked
the original image (previous to applying the zoom feature) will be added to
the pool of images that are displayed on the SkyView Image Gallery.
The images will also be randomly selected to appear on the main SkyView page.
Direct all questions regarding SkyView to our Feedback Page
SkyView has been developed with generous support from the NASA AISR
and ADP programs (P.I. Thomas A. McGlynn)
under the auspices of the High Energy
Astrophysics Science Archive Research Center (HEASARC) at the NASA/
Astrophysics Science Division.
We gratefully acknowledge the support of NASA and contributors
of SkyView surveys.