CRISM pointing sign conventions

Dave Humm 19 May 2006

  • Nominal CRISM base, spacecraft, and HiRise coordinate systemsare the same

  • Nominal base z is nadir, y is perpendicular to z and to spacecraftvelocity, x is approximately in direction of spacecraft velocity

  • The CRISM image coordinate system is described in a later slide

Mars

S/C velocity

CRISM base coordinates

  • Display column number 0 on left, 639 on right

    • Display line number with line 0 as top line

      • Line number 0 corresponds to the first frame taken

      • REACT displays images this way, so they will be correct

      • I’m not sure of the convention for PNG images, but I think browse productsare displayed with 0 the bottom line so they are mirror images [5/12/2006]

    • Ground plane image is oriented as one would see

      • Flying on the spacecraft feet first

      • Looking out the CRISM telescope at Mars

      • Anti-sunward radiator is one’s left ear

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  • Will be – for column 0 and + for column 639

  • This is opposite the sign of the yaw angle from the calibration lab

  • Zero degrees is defined as perpendicular to the gimbal axis

    • Home and zero are the same

      • Nominally nadir

      • Used for mapping mode eventhough not exactly nadir

    • Gimbal angle signdefinitions

      • Commanded angle in microrad + looking forwardalong track, - looking back

      • Encoder counts + looking backward along track, looking forward

      • Note: For CRISM theodolite alignments and for pre-envcalibration, commanded angle in microrad + lookingbackward along track, looking forward

Mars

S/C velocity

CRISM base coordinates

  • Designed so increasing x is increasing column number and increasing y isincreasing line (frame) number in the ground plane image

  • z axis is exactly along the boresight and approximately perpendicular to thegimbal axis. The x axis is in the plane of the boresight and the gimbal axis. The x axis is approximately along the gimbal axis and pointed away from the anti-sunward radiator

  • When a target on Mars is imaged at a larger column number (larger pixel angle),the x-component of the unit vector pointing from CRISM to that target is larger

  • When a target on Mars is imaged at a larger line number (that is, later), the y-component of the unit vector pointing from CRISM to that target is larger

  • The image coordinate system rotates as the gimbal rotates, while the basecoordinate system is fixed to the spacecraft bulkhead

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