More robust (and convenient) astrometric reduction

There are certain limits to consider triangles similar when SIPS matches images with other images or with catalog plate. The default value of this limit was 0.001 (0.1%) of side ratios. This limit is enough to reliably test similarity of star patterns on images acquired with optics well enough maintaining tangential projection (or on images to which Field Curvature Correction was applied — see SIPS documentation for explanation how Field Curvature Correction works). Unfortunately good enough tangential projection is not the case of images acquired through any type of field corrector, be it coma-corrector for Newtonian telescopes or field-flattener for refractors and RCs.

While it is enough to simply increase this limit in the Image/catalog matching parameters dialog box when the field is distorted and no Field Curvature Correction is applied, users typically did not check this possibility. This is why the new default value is five-time greater.

Another default parameter changed is the number of plate span, which should be used for catalog matching. The original default value 1 (one field of view size) worked properly when the image center coordinates were sufficiently precise (approx. to within 1/3 of the frame size). When the used telescope mount returned image center coordinates with greater error, the astrometry plate match could fail.

Again it is easy just to increase the number of plate span to increase the catalog area, which SIPS tries to fit, but when users omitted to do so, astrometry reduction failed. So the new default value is 5, but if previous version of SIPS was installed on the particular computer, also the plate span remains defined in the configuration file and has to be enlarged manually.

The matching catalog plate overlay displayed within SIPS images was only scaled and translated to fit the field of view, but not rotated or mirrored. This was not a problem, when the processed images was properly oriented according to conventions (north on the top, east on the left). But while other orientation was used, the overlay display was hardly usable despite astrometry reduction of course works without problems regardless of the image orientation.

New SIPS v3.5 uses all transformations including rotation and also mirroring to show the best overlay possible.

This update is also reflected in the Manual plate match with catalog dialog box, where two new controls allow definition of mirroring and rotation for the displayed catalog overlay.

Previous SIPS versions did not distinguish between binned and unbinned pixels. If the pixel binning was used, appropriately larger pixel size has to be defined in the Plate astrometry information dialog box (e.g. for 9 m pixels and 2 × 2 binning, the pixel size has to be defined as 18 m). SIPS v3.5 maintains used binning using XBINNING and YBINNING FITS keywords, so the pixel size should remain always the same to properly calculate angular (binned) pixel size.

Pixel binning count boxes were also added the Manual plate match with catalog dialog box.

Bug fixes and new functions in Photometry

The Choose from opened images dialog box allowed to select only images acquired through defined filter of images with certain exposure time, but it was not possible to select images fulfilling both conditions (defined filter AND certain exposure time). This is why the dialog box was redesigned. Now the selection is not performed immediately after choosing of combo-box value, but with explicit button click. If both filters are defined, both are used to filter images. Any filer can be set to <ignore> value and only the other filter is then used.

Photometry report comment line now includes new keyword “Filter:”, which can be used by post-processing software to distinguish among individual colors.

The Photometry Report dialog box newly allows to automatically add date, time and used filter to the report file name. It is purely a question of personal preferences whether to save reports to different folder under the same name of to same folder under different names. Either way, SIPS now allows both variants, so every user can choose what better suits to him or her.

Unfortunately the significant changes of internal computing thread organization, introduced in SIPS v3.4.1 to speed-up processing on AMD Ryzen processors (the speed-up was more that twice, so it was very important), introduced one synchronization problem during image matching. Sometimes the internal state was corrupted by simultaneous access of more computing threads without proper synchronization and SIPS could fail e.g. during image stacking or photometry processing. Probability of this error was higher if the multi-core CPU does not support hyperthreading (e.g. Core i5). This problem is fixed in v3.5.

Another fixed problem caused SIPS failure when the photometry series contained image(s) without single star detected (e.g. images acquired when clouds passed the field of view of completely saturated images etc.) and when the user selected one star as variable, comparison or check and then deselected the same star again.

General bug fixes

The observatory location is defined in the telescope mount control tool, but it can also be specified in the New FITS Header tool to be stored into FITS headers. While SIPS internally keep all angle values in radians, the FITS header should maintain geographic location expressed in degrees. Previous versions of SIPS improperly converted between degrees and radians in the New FITS Header tool, so the location information was corrupted.

Previous version of SIPS stored very slightly different exposure time in the FITS header of the last image in series (acquired using the Series tab of the Imaging Camera tool). Now all exposure times are stored correctly. What is more, SIPS added rounding of exposure time to 0.001 s to eliminate more digits in the exposure time value without any real meaning (for instance the shortest exposure time of the astronomical cameras is often hundred times longer).

SIPS can record video sequences, but uses functionality provided by Windows video subsystem to do so. To allow the users to choose desired video codec, SIPS tries to enumerate all codecs installed in the particular OS. Unfortunately codecs are libraries dynamically linked into SIPS process, so every problem in the codec DLL negatively affects the SIPS itself. Obviously there are some bugs in the 64bit version of the Logitech codec installed together with Logitech web cameras. This bug caused 64bit SIPS semi-random crashes on computers with Logitech cameras and software installed upon opening the Camera or Context camera tool windows (these two tools can save videos). The solution is skipping of the particular Logitech codec during enumeration (we hope no user will miss it) and as a second measure, to handle possible codec failures using structured exception handling.

Important bug was fixed in the 64bit version of SIPS. One structure was not properly initialized upon SIPS startup and this could lead to a process failure during its launch. Please note this problem affected only 64bit version of SIPS and the failure occurred only with low probability. When SIPS stared successfully, the bud no longer affected its execution.

ASCOM platform compatibility issues

Some user noticed problems running SIPS v3.4.1 on computers, where latest ASCOM platform v6.3 was installed, particularly when a telescope mount was connected through ASCOM telescope driver. What looked like some issue of compatibility among ASCOM platforms resulted into problems with .manifest file version in our ASCOM drivers. This problem is fixed and SIPS v3.5 works with all ASCOM devices reliably also under latest ASCOM platform versions.

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