Control of image overlays

SIPS v3.3 unified ways to control the astrometry-related overlays displayed above the images in SIPS. In principle, it is possible to highlight stars found within the image (with green circles) and if the image is matched with catalog, corresponding catalog star positions are marked with red circles and orange line connecting green star circle with red catalog circle indicates the match. The respective check-buttons, located in both Astrometry and Photometry tool windows, are now synchronized and they state applies to all images regardless if displayed in independent image window or in other tools.

Astrometry with uncertain image center coordinates

Attention was paid to increase robustness of the astrometry match when the image center coordinates are not know precisely. SIPS v3.3 now can find proper match even if the image coordinates are known only roughly, the uncertainty can be a multiply of the image angular dimensions. It is enough to define span of the catalog plate in the Image/catalog matching parameters dialog box and SIPS searches much wider area when trying to match image and catalog stars. Of course searching of much larger area needs some time, but astrometry if optimized to be very fast so the match need only a couple of seconds on typical PC.

This functionality can be very useful for centering of the target field in the case the mount cannot goto with enough precision. The Astrometry tool allows syncing of the mount controller with the detected image center coordinates, so the target field can be found with much higher precision, especially if the whole process involving astrometry match of the field and mount syncing is repeated several times.

Photometry batch processing

Photometry processing can be time consuming (despite all optimizations and parallel processing implemented in SIPS). Especially finding of all stars on large images and the photometry calculation for tens of thousands stars for every image need time. Typically the user needs to invoke individual steps by separate clicks (Find star and match images, Calculate astrometry, Calculate photometry). New SIPS introduced a new command button “Photometry Batch”, which performs all these steps in series, so the user does not need to pay attention to the process until all three steps finished.

Automatic calculation of optimal aperture in Photometry

Automatic calculation of the optimal aperture in the Photometry tool requires propagation of the single resulting aperture value through all images in the photometry series else the measured flux may vary. But the unification of the aperture did not work reliably in all cases in previous SIPS versions, sometimes different aperture was used on a few images. Such measurements have to be skipped or manually set aperture has to be used. SIPS v3.3 fixed this problem and automatically calculated optimal aperture is always used on all images.

Wider set of FITS headers

FITS files allow definition of any parameter in its header (only a few parameters are obligatory), which makes the standard very flexible, but at the same time this freedom leads to terrible situations when multiple software packages need to cooperate. Individual programmers chose arbitrary and mutually different keywords for the same information. For instance image center coordinates may be defined using RA and DEC keywords, but some software packages use OBJCTRA and OBJCTDEC keywords, while other packages use OBJRA and OBJDEC keywords. Pixel angular size si similarly defined using PIXSCAL keyword, while SECPIX and SECPPIX are also used. New alternative keywords are continually added to every new version of SIPS to allow as wide interoperability as possible. Reports of unsupported FITS keywords are welcome so they support can be included into new SIPS versions.

Astrometry plate parameters calculation

While previous SIPS version required pixel angular size to be defined prior to astrometry image solution, new SIPS version can use the focal length and pixel physical dimensions to calculate angular pixel size. Of course the Plate parameters dialog box still allows explicit definition of these parameters:

If also the pixel physical dimensions and focal length of the used telescope are undefined in the particular image, SIPS tries to use default values for these parameters. These default values are somewhat hidden in the New FITS Header tool window. But this tool window has to be used if we want to include pixel physical dimensions and focal length parameters into every acquired image, so the user simply has to type these parameter values here.

SIPS is a freeware and can be downloaded from the Download section of this web site.