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Generating Test Kernels for an image

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Jesse Mapel edited this page Aug 22, 2019 · 7 revisions

Example data is at /work/users/jmapel/ale_kern_data

Pick and image and spiceinit it

spiceinit from=EN1072174528M.cub

Copy all of the kernels listed in the kernel group of the image

  Group = Kernels
    NaifIkCode                = -236820
    LeapSecond                = $base/kernels/lsk/naif0012.tls
    TargetAttitudeShape       = $messenger/kernels/pck/pck00010_msgr_v23.tpc
    TargetPosition            = (Table, $messenger/kernels/tspk/de423s.bsp)
    InstrumentPointing        = (Table,
                                 $messenger/kernels/ck/msgr_1504_v01.bc,
                                 $messenger/kernels/ck/msgr_mdis_sc040812_1504-
                                 30v1.bc,
                                 $messenger/kernels/ck/msgr_mdis_gm040819_1504-
                                 30v1.bc, $messenger/kernels/fk/msgr_v231.tf)
    Instrument                = $messenger/kernels/ik/msgr_mdis_v160.ti
    SpacecraftClock           = $messenger/kernels/sclk/messenger_2548.tsc
    InstrumentPosition        = (Table,
                                 $messenger/kernels/spk/msgr_20040803_20150430-
                                 _od431sc_2.bsp)
    InstrumentAddendum        = $messenger/kernels/iak/mdisAddendum009.ti
    ShapeModel                = Null
    InstrumentPositionQuality = Reconstructed
    InstrumentPointingQuality = Reconstructed
    CameraVersion             = 2
  End_Group

Determine the start and end time for the image

Always use the SCLK string for the start time

For a framing instrument the stop time is start time + exposure duration. For a line scan instrument the stop time is the start time + exposure duration * number of lines

    SpacecraftClockCount  = 2/0072174528:989000
    ExposureDuration      = 1 <MS>

You will also need to account for light time correction. See this gist for an example and code: https://gist.github.com/jessemapel/d99db43cbf7fe9277d4def638532d053

CKs

Determine what reference frames are in your CKs

CKs always end in the extension .bc so look for those files.

Use the ckbrief utility to see which frames are in each CK. The Object is the frame ID

(ale) igswzawglt1183:data jmapel$ ckbrief msgr_mdis_sc040812_150430v1.bc
 
CKBRIEF -- Version 6.1.0, June 27, 2014 -- Toolkit Version N0066
 
 
Summary for: msgr_mdis_sc040812_150430v1.bc
 
Object:  -236000
  Interval Begin ET        Interval End ET          AV
  ------------------------ ------------------------ ---
  NEED LSK AND SCLK FILES  NEED LSK AND SCLK FILES  Y

Slice the CKs

For each frame in each CK extract the information for that frame for the image time. Use the ckslicer tool which you will need to download from NAIF's website. The ckslicer usage docs are quite good. Here's what to pass for the arguments:

  • -LSK : your leapsecond file. It should look like naif####.tls
  • -SCLK : your sclk file. It should end in .tsc
  • -INPUTCK : the name of the CK you are extracting from
  • -OUTPUTCK : The name of the file you are putting the information in
  • -ID : The NAIF ID of the frame you are extracting the information for
  • -TIMETYPE : SCLK
  • -START : The starting SCLK string
  • -STOP : The ending SCLK string

To get the stop time as an SCLK string use the following call in spiceypy: spice.sce2s(<the ID code for your spacecraft>, spice.scs2e(<the ID code for your spacecraft>, '<your starting SCLK string>') + <the exposure duration for the image>)

You can look up your spacecraft's id here

Replace the comments from your CKs

The CKs can have really long comments so remove them with commnt -d <your new CK file>. Next, write your new comment to a text file. I'd suggest something like:

This CK is for testing with the image <your image file name>

This CK was generated using the following command
<your ckslicer command>

Then, attach the new comment with commnt -a <your new CK file> <your text file>.

Convert your CKs to transfer format

Use the command toxfr <your new CK file> to convert the files. They should come out with the extension .xc.

SPKs

Determine your spacecraft and target IDs

You need to find the ID of your spacecraft and target. Look on Naif's website.

Slice the SPKs

To slice the SPKs, use spkmerge with a config file. You will need two config files; one for the spacecraft and one for the target. The config files should look like this:

LEAPSECONDS_KERNEL     = <Your LSK kernel>
      SPK_KERNEL             = <the SPK your are creating>
         SOURCE_SPK_KERNEL   = <the SPK your are extracting from>
            INCLUDE_COMMENTS = no
            BODIES              = <the ID code of either your spacecraft or target>
            BEGIN_TIME          = <the start time of your image as a UTC string>
            END_TIME            = <the stop time of your image as a UTC stirng>

To get the UTC strings use the following line in spiceypy: spice.et2utc(spice.scs2e(<your spacecraft ID>, '<your SCLK string>'), 'c', <How many decimals past the second you want>) I recommend at least 3 decimals past the second. IE:

>>> spice.et2utc(spice.scs2e(-236, '2/0072174528:989000'), 'c', 3)
'2015 APR 24 04:42:19.666'

Convert your SPKs to transfer format

Use the command toxfr <your new SPK file> to convert the files. They should come out with the extension .xsp.

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