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.
Value of this parameter is preserved in user's
configuration file, so the new default value is not used if there
already exists configuration file with different value, saved by
some previous version of SIPS. In such case it is necessary to
change this value manually.
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.
If the image center coordinates are significantly wrong
by many sizes of the field of view, do not hesitate to increase
plate span to 10 or more field of view angular sizes. Matching is
very fast in SIPS and it is easy for the software to look around
to test if the star pattern matches.
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
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
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.
If the pixel angular size is already stored in FITS or
similarly if the binned pixel dimension is stored as pixel
dimension together with binning, then there can be some
discrepancy among pixels dimension, binning, focal length and
pixel angular size. Always check these parameter prior astrometry
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
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
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
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
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
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.