This document is retained for historical interest.
team has released a new Java-based geometry engine to
replace the IDL-based version that has been used for many years.
Users should see some substantial
improvements in a number of areas but the primary motivation
was to allow us to easily distribute functionality in
a non-proprietary environment.
- More Robust Mosaicking Algorithm
When mosaicking component images of a survey together, a new and
more robust algorithm is used. This should eliminate small regions
that ran past the edge of the source images that were sometimes
seen in previous versions. The new algorithm should generally
find the 'best' image for each pixel in the image.
- New Resampling Algorithms
A new set of 'high-order'
resampling algorithms is available. These
allow for use of Lanczos resamplers with kernels of a user specified
size, and for second to fifth order spline resamplers.
An efficient exact-area resampler has been developed to replace the
very slow and buggy triangular decomposition resampler used in the IDL
version. This is useful when exact conservation of flux is required
or where the original data is poorly sampled or incomplete.
Currently supported samplers include:
Nearest Neighbor (NN)
Bi-linear interpolation (LI)
Splines from 2-5 order (Spline or Spline3, Spline2, Spline4, Spline5)
Lanczos interpolation with a specified kernel size
(Lanczos, or LanczosN where N >= 2, the default is 3)
exact-area resampling using Sutherland-Hodges clipping (Clip).
The default is Nearest Neighbor.
- Faster Image Generation
The Java-based system uses far less memory than in IDL, so that larger
images can be generated and large images are generated more quickly.
Images of up to 5000x5000 pixels can be generated while the
previous version was limited to about 2000x2000 pixels.
- Quick Introduction of New Survey Data
New surveys can be introduced more quickly. Access to remote tools that
support the new Virtual Observatory Simple Image Access Protocol requires the
creation of only a single XML file that describes where the file is to be found.
When special feature are needed to address a survey they can be added in a way
which does not clutter the standard code. The SDSS DR3 is one survey that
has been made available through this mechanism.
- New Edge Adjustment Algorithm
A new edge adjustment algorithm
is available whose invocation can
be controlled by the user. Edge-adjustment attempts to hide the visible
boundaries between source images caused by differing background levels in
the source image. The older version used a median test where the medians
of images were matched. The new version matches along the edges associated
with pairs of images and can be turned on or off (but is turned on by
default for the DSS).
- Code Available for Download
The Java source code is available for download and
runs in a non-proprietary
environment. A standalone executable JAR file for SkyView will soon be
available. The Java code is designed to allow users to easily
add there own surveys and functionality.
We have changed a few things in the defaults for returned images
that may affect some users. Please let us know if you have serious
- The default color table for images is now Black&White rather
than the IDL Stern Special (which is still available).
- Images are now returned by default as 8-byte reals with an
option for 4-bytes. [No longer true.]
- Quicklook data now uses JPEG files. GIF and other formats
are also available.
- The internal directory structure used for the creation
of FITS and quicklook data has changed. Users of the undocumented
RETURN=filename option will need to modify their code.
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.