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Posted by: Nirgal Apr 29 2010, 02:33 PM

Does anyone know if/where there are map projected CTX images avilable ?

There are the EDR (i.e. raw) data sets as IMGs at PDS, but so far there seem no RDRs (i.e. calibrated and map projected) versions of the CTX images publicly available (yet?)

However, when I'm looking at the tight CTX image integration in Google Mars it seems that they have the exact footprint data of all CTX images readily to be overlayed with the global Mars/MOLA/HRSC map ...

So somehow the map projection of CTX images/footprints must have been done at least for Google Mars.

Ross Beyer even has a link on his web page to the footprint data of all CTX images as KML files:
http://pirlwww.lpl.arizona.edu/~rbeyer/kml/CTX_PDS.kml

So I'm courious, if the complete map projected CTX image data exists somewhere or if it is required to do the projection for each image oneself with the usual ISIS tool chain only ?

Background: what I really want to do is to merge/overlay map projected HiRISE images with their corresponding CTX observation as a kind of "background"-layer ... Ideally this should be performed with pixel-precision which, of course, requires exact map projection from one
camera's space to the other.

Probably this must have been done before, but I couldn't find enough information on this in the ISIS doc & ISIS/GIS community forums.

Thanks in advance for any help !

Bernhard

Posted by: elakdawalla Apr 29 2010, 05:19 PM

Bernhard, I imagine Doug will reply before long with tales of the pain he has gone through to reproject the CTX images, but it involves ISIS. The Google map overlays probably have nothing to do with the image files; I imagine they are simple polygons, rectangles made using the latitude/longitude coordinates of the four corners of each image. That lat/lon information is available in the headers of the images, of course.

If there are one or two images that might be of interest to a lot of people, I have a friend who I can beg to provide map-projected versions. But if you need more than that, you're going to have to figure out how to run ISIS, I think!

Posted by: djellison Apr 29 2010, 08:27 PM

It's fairly easy - just follow this from end to end :
http://isis.astrogeology.usgs.gov/IsisWorkshop/index.php/Working_with_Mars_Reconnaissance_Orbiter_CTX_Data

Posted by: Nirgal Apr 29 2010, 10:57 PM

ok thank you Emily, Doug !

So it is definitely going to involve ISIS, as I have already suspected.

As far as the radiometric calibration is concerned I wrote my own C++ program some time ago using the source code in the ISIS program "ctxcal" as a reference -> that produced reasonable results converting the IMGs to calibrated 16 Bit Tiff/PNG.

However things are not so easy with map projection (without the SPICE kernels and such

So in the mean time I am in the process of downloading the whole ISIS installation (30+ Gigs ) to be run in a Linux VM....

The following quotes I found from the ISIS support forum might also be helpful:

Posted by: tharrison Apr 30 2010, 04:24 AM

Posted by: djellison Apr 30 2010, 04:30 AM

QUOTE (Nirgal @ Apr 29 2010, 11:57 PM)

Posted by: JohnVV May 1 2010, 06:34 AM

the thread is a bit old but cartrite was doing some ctx images ( yes in isis3) over on celestia matters
http://forum.celestialmatters.org/viewtopic.php?t=194

the isis thread is a bit long 19 pages .

Posted by: Nirgal May 1 2010, 09:07 AM

thanks for the hint, John !

QUOTE (JohnVV @ May 1 2010, 08:34 AM)

Posted by: Nirgal May 1 2010, 01:44 PM

Meanwhile I found that I don't have to wait for the whole download to finish because all the files needed for CTX processing have already been transferred.

So I gave it a try and it seems to work so far

Here is my first ISIS-map projected CTX image, showing Oppys travel area between Victoria and Endeavour, re-projected with the same mapping parameters than the corresponding HiRISE-observation PSP_010341_1775.