Processing Chandrayaan 2 OHRC Images¶

More info on Chandrayaan 2:

The OHRC (Orbiter High Resolution Camera) is a panchromatic pushbroom camera with a ground sample distance of about 0.25 m. The ingestion workflow is the same as for TMC-2, with one intentional difference in how the SPICE kernels are sourced (see the note below).

Environment¶

You will need:

ISIS 10.0.0_RC2
ALE >= 1.1.3
SpiceQL >= 1.2.7
usgscsm

To install these with conda:

conda create -n ch2 \
    -c usgs-astrogeology/label/RC \
    -c conda-forge \
    matplotlib isis=10.0.0_RC2 ale=1.1.3 usgscsm=2.0.2
conda activate ch2 # activate env

ISIS 10 release candidate

ISIS 10 has not been formally released yet, so the command above installs the 10.0.0_RC2 release candidate from the usgs-astrogeology/label/RC channel.

Image Data, Label, and Template¶

The .img image and .xml label are required to import an OHRC image into the ISIS cube format. These can be downloaded from ISRO's interactive map or ISRO's PRADAN system for bulk downloads. (New users must register an account.)

SPICE Kernel Coverage

Chandrayaan 2 SPICE kernels are distributed through the ISIS data area and fetched with downloadIsisData chandrayaan2 $ISISDATA (see the next section). Coverage may still lag for the most recent acquisitions. You can check which kernels are available with the following CURL command:

curl -XGET "https://astrogeology.usgs.gov/apis/spiceql/latest/searchForKernelsets?spiceqlNames=\[chandrayaan2\]&limitCk=-1&limitSpk=-1" | jq

The filenames for CKs and SPKs tell you their time coverage.

Set Environmental Variables¶

ISIS requires ISISROOT and ISISDATA to be set. You can set ISISROOT equal to the CONDA_PREFIX. You will need to set up the ISIS Data Area and set ISISDATA to point to it, with at least the base and chandrayaan2 areas installed:

downloadIsisData base $ISISDATA
downloadIsisData chandrayaan2 $ISISDATA

Create an ISIS compatible Cube or GTiff¶

Import the image with isisimport, attach the kernels with spiceinit, then create the ISD with isd_generate:

isisimport from=ch2_ohr_ncp_20211228T2209123959_d_img_d18.xml to=ch2_ohr_ncp_20211228T2209123959_d_img_d18.cub
spiceinit from=ch2_ohr_ncp_20211228T2209123959_d_img_d18.cub
# create an ISD; this writes ch2_ohr_ncp_20211228T2209123959_d_img_d18.json
isd_generate -k ch2_ohr_ncp_20211228T2209123959_d_img_d18.cub ch2_ohr_ncp_20211228T2209123959_d_img_d18.cub

Why OHRC uses spiceinit and isd_generate -k

Unlike the TMC-2 workflow, which reads kernels from the local data area with isd_generate -s, OHRC runs spiceinit first and then isd_generate -k. For OHRC, spiceinit cleanly attaches the SPICE kernels to the cube, so -k reads them directly from the cube. This is the most reproducible path from a fresh downloadIsisData, as it does not require any local metakernel setup. The -s approach used for TMC-2 also works if you prefer to read kernels from the local ISISDATA area.

The cube name appears twice on purpose: -k <cube> points isd_generate at the SPICE kernels attached by spiceinit, and the second occurrence is the input image the ISD is generated for.

You can troubleshoot isd_generate with -v. The most common issue is missing kernels covering the image's time range.

Check you have the files; you will need the .json and .cub:

ls -1
# ch2_ohr_ncp_20211228T2209123959_d_img_d18.cub
# ch2_ohr_ncp_20211228T2209123959_d_img_d18.img
# ch2_ohr_ncp_20211228T2209123959_d_img_d18.json
# ch2_ohr_ncp_20211228T2209123959_d_img_d18.xml

From here you can use the .cub and .json for any CSM compatible tool like Socet GXP or Ames Stereo Pipeline.

Create an ISIS-compatible image¶

To use this image in ISIS, you will need to combine the JSON ISD with the cube. These can be written as an ISIS Cube or GTiff. We recommend GTiffs given the large size of CH2 images.

mamba install usgscsm # if not installed already
csminit from=ch2_ohr_ncp_20211228T2209123959_d_img_d18.cub isd=ch2_ohr_ncp_20211228T2209123959_d_img_d18.json
cubeatt from=ch2_ohr_ncp_20211228T2209123959_d_img_d18.cub to=ch2_ohr_ncp_20211228T2209123959_d_img_d18.tiff+GTIFF

You can view the image with qview, qgis, or other tools designed for spatial data. The image is large and may take a moment to render.

qview ch2_ohr_ncp_20211228T2209123959_d_img_d18.tiff

From here you can use the image in other ISIS apps such as footprintinit and cam2map. Initial pointing in OHRC has errors (as with most instruments), so bundle adjustment is necessary for accuracy.

See for bundle adjustment info: https://astrogeology.usgs.gov/docs/how-to-guides/image-processing/bundle-adjustment-in-isis/

See for OHRC stereo info in ASP: https://stereopipeline.readthedocs.io/en/latest/examples/chandrayaan2.html