SkyView version 3.5.2 is now available for testing. There are two changes to surveys and one to the underlying code. The data for the GLEAM surveys has been updated with substantial improvements in coverage. The problem with the SDSS surveys noted in the prior post is fixed in the associated SkyView-in-a-Jar file everything points to DR9 now.
The code change involves the Spline Sampler. Previously this sampler did nothing special when it encountered a NaN in the input data. It simply used that value. The way the Spline sampler works is that if first computes a grid of spline coefficients and then uses those to interpolate at requested positions. However any arithmetic operation involving a NaN results in a NaN, so if there are NaNs at the edges of an image, they’ll tend to propagate throughout the image.
This is the case for the GB6 radio survey (at least), so if you used the Spline sampler on this survey, nothing was returned — or more precisely an array of NaNs. David Green noted this behavior and we’ve changed how SkyView handles NaNs in splines.
There is now a new setting, SplineNaNs, which you can use in the SkyView Jar. The default — used in Web pages — is SplineNaNs=min. This replaces all NaNs with a value 10% of the total range less than the minimum value. Other options are max, which uses a value 10% greater than the maximum value, skip, which duplicates the prior behavior (i.e., we do nothing to handle the NaNs). Or you can specify a number (other than 1) to use as the value for the NaNs.
We’re still testing v3.5.2 but it should be released in a few days.