DSS Image Blink Comparator MaximDL Plugin
Based on a recent discovery of a variable star in M27 by an acquaintance that routinely performs blink comparisons on images he takes, I decided to write a MaximDL plugin to automate the process.
The plugin examines the supplied user image and extracts the RA and Dec
coordinates of the image and calculates the horizontal and vertical field of
view of the image.
Using these, it then connects to the Digitized Sky Survey (DSS) archives at
STSCI and downloads a 16bit FITS file for the corresponding coordinates and
FOV.
Once downloaded, it performs a vertical flip on the image to orient it to the
MaximDL coordinate system then performs an auto-alignment, using star-matching.
If this succeeds, it proceeds to perform a blink between the user image and the
scaled and rotated DSS image.
This should allow any differences to be readily determined, possibly leading to
your own variable star, nova or supernova discovery!
If you are lucky enough to find anything using my plugin, please do let me know – you can even mention my plugin in your discovery notice if you like J
Usage:
The initial user image must have the RA and Dec co-ordinates set in the FITS
header, either RA/DEC or OBJCTRA/OBJCTDEC. It must also have the horizontal and
vertical pixel size and the telescope focal length to allow the calculation of
the image FOV.
It is recommended the user image is plate solved with Pinpoint first to get the
exact image center and rotation angle.
The image from DSS is saved to disk as “dss_reference_image.fit” in
the same directory as the dss_blink.dll file is located.
If the auto-align fails due to a shortage of identifiable stars, in the two
images - sometimes it gets a bogus match and scales the DSS image right down to
what it thinks the match is. If this happens, you can simply select the DSS
image and click "undo" which reverts it to the downloaded format,
then use a different alignment scheme - I often use Pinpoint to plate solve the
DSS image then use the astrometric alignment method.
The FITS images from the DSS archive are limited to a maxim FOV of 60
arc-minutes in each axis.
The DSS image is set to “moon” screen-stretch for the blinking, but
after the user cancels the blink, the DSS image is left open in case
screen-stretch adjustment is needed to make the DSS image match the user image
more closely in terms of depth.
The dialogue box displaying the user image RA/DEC coordinates is editable. If a
comma is used as the decimal point separator on your system, the plugin will
automatically convert it to a period as it retrieves the reference DSS image
from the archive.
Note that the DSS FITS images can be quite large, so a broadband connection is strongly recommended. A 35arcmin square image is about 7.5MB. Download times are obviously affected by the image FOV and connection speed.
If you get an error stating that the MSINET.OCX file can not be found, you can download it from the official Microsoft site here:
MSINET.CABThis was an early utility from me and I didn't make an installer - the installer should really install that file.
Config options:
· None
Version history:
v1.0 - Initial release.
v1.1 – Uses Pinpoint image co-ordinates if available, plus uses the
Pinpoint image rotation figure to download enough extra around the user image
to ensure the corners are filled in once the DSS image is rotated to match. DSS
image now set to “low” stretch and is left open once the blink is
complete.
v1.2 – The RA/DEC coordinates are now editable. Commas in the RA/DEC will
be automatically converted to periods as the DSS archive image is downloaded
for compatibility with the archive. The default screen-stretch of the DSS image
has been changed to “moon”. The default blink period is now 1
second. The downloaded DSS image is now saved to disk as
“dss_reference_image.fit” in the same directory as the
dss_blink.dll file is located.
v1.3
- Resize DSS image to match scale of user image, to increase chance of
auto-star matching working. Set scale keywords in DSS image to make
plate solve easier for user, if required.
If you download this to give it a go, please post feedback on the Yahoo
group, or email me directly at: winfij_AT_gmail_DOT_com
One final note - if you have any errors, please note the exact error messages
and let me know!
Regards,
John