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CRISM CAT projection


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I notice that when I use the CAT 7.2.1 - Map Utilities - Project Single Cube Data tool, I obtain a different result than when I use the Build GLT tool in ENVI, with:

X Geometry band = Band 5 of the associated DDR

Y Geometry band = Band 4 of the associated DDR

according to the instructions here on slide 23.




Looking at the IDL projection_event.pro, I see that the lat and lon keywords are defined as follows:

  ; Pull some planes from the geofile
  lat = envi_get_data(fid=geofid,dims=dims,pos=3)
  lon = envi_get_data(fid=geofid,dims=dims,pos=4)


Should this be bands 4 and 5 (as in the walkthrough slides) rather than 3 and 4?


The filename I am using is: /home/Raw/frt00003e12_07_if166l_trr3_CAT_corr_SUM_classified_noProj.img


I know in find_geofile.pro that an automatic search is done for the ddr associated with the default trr3 name, but I'm not sure if it would find the ddr associated with mine as the filename has been altered from the standard CAT convention.


Essentially I am wondering which projection method is more correct.






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Hi Elyse,


I verified that the lines in projection_event.pro do pull latitude and longitude from the DDR file. The 'pos' keyword to envi_get_data is zero-offset - so the first band is pos=0 etc. The two lines you quote pull the 4th and 5th bands - lat and lon - as they should. I think the walkthrough slides and probably the Build GLT tool are numbering the bands starting at 1, so 4 & 5 in the slides is really the same as 3 and 4 in the code.


I think the DDR search should find the DDR for your file if it's located in the same directory, despite the filename additions, as long as the root 'frt00003e12_07_if166l_trr3..' matches. I think you would see a failure if it didn't find a DDR; it wouldn't generate results that differed from expected.


How big is the difference you see? Tiny differences might be explained by roundoff, different calculations etc. I can dig deeper if the difference is significant.



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