SkyView Java Engine

This document is retained for historical interest. The SkyView 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.
Gotchas... 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 problems.
- 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.

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