KPL/IK CTX Instrument kernel =========================================================================== This instrument kernel (I-kernel) contains MRO Context Camera (CTX) optics, detector, and field-of-view parameters. Version and Date --------------------------------------------------------------------------- Version 1.1 -- August 23, 2012 -- Boris Semenov, NAIF/JPL Replaced ``mroctxAddendum001.ti'' with ``mroctxAddendum005.ti''. Version 1.0 -- June 7, 2007 -- Boris Semenov, NAIF/JPL Initial release. References --------------------------------------------------------------------------- 1. ``Kernel Pool Required Reading'' 2. ``C-kernel Required Reading'' 3. MRO Frames Definition Kernel (FK), latest version. 4. MRO CTX CDR Package, March 20, 2003. 5. ``mroctxAddendum005.ti'' IK file by USGS, Flagstaff, included ``as is'' at the bottom of this IK. 6. CTX Description, MSSS Web Site, http://www.msss.com/mro/ctx/ctx_description.html Implementation Notes -------------------------------------------------------- Applications that need SPICE I-kernel data must ``load'' the I-kernel file, normally during program initialization. Loading the kernel using the SPICELIB routine FURNSH causes the data items and their associated values present in the kernel to become associated with a data structure called the ``kernel pool''. The application program may then obtain the value(s) for any IK data item using the SPICELIB routines GDPOOL, GIPOOL, GCPOOL. Routine GETFOV may be used if the file contains instrument field-of-view (FOV) specification. See [1] for details. This file was created with, and can be updated with a text editor or word processor. Conventions for Specifying Data -------------------------------------------------------- Data items are specified using ``keyword=value'' assignments [1]. All keywords referencing values in this I-kernel start with the characters `INS' followed by the NAIF MRO instrument ID code, constructed using the spacecraft ID number (-74) followed by the NAIF three digit ID number for CTX (021). This ID is defined in [3] as follows: Instrument name ID -------------------- ------- MRO_CTX -74021 The remainder of the keyword is an underscore character followed by the unique name of the data item. For example, the focal length of the CTX is specified by INS-74021_FOCAL_LENGTH The upper bound on the length of all keywords is 32 characters. If a keyword is included in more than one file, or if the same keyword appears more than once within a single file, the last assignment supersedes any earlier assignments. Overview -------------------------------------------------------- From [5]: From its 3 p.m. circular, polar orbit, the MRO Context Camera (CTX) will obtain grayscale (black-and-white) images of the martian surface with a spatial resolution of about 6 meters (20 feet) per pixel over a swath that is about 30 kilometers (18.6 miles) wide. CTX is a Facility Instrument, operated by Malin Space Science Systems and the MRO MARCI science team. As its name implies, CTX will provide context for images acquired by other instruments onboard the Mars Reconnaissance Orbiter, particularly the High Resolution Imaging Science Experiment (HiRISE) and the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). The instrument consists of a 350 mm focal length, 6 degree field of view, catadioptric Cassegrain (Maksutov-type) telescope that images onto a 5064 pixels-wide charge coupled device (CDD) line array. The CCD detects a broad band of visible light from 500 to 800 nanometers in wavelength. The instrument includes a 256 MB DRAM buffer, so that it can acquire pictures that have downtrack lengths greater than 160 kilometers (99 miles). In other words, a typical CTX image can be as wide as 30 km and as long as 160 km, or more. Mounting Alignment -------------------------------------------------------- Refer to the latest version of the MRO Frames Definition Kernel (FK) [3] for the CTX reference frame definitions and mounting alignment information. Apparent FOV Layout -------------------------------------------------------- This diagram illustrates the CTX apparent FOV layout in the corresponding reference frame and the CCD corner based pixel scheme: ^ | direction of | flight | ^ +Xctx (along track) | | | | ~0.001146 degrees | | | v Pixel 1 | Pixel 5000 --- +---------|---------+ | 1 line | 2500.5x-------------> +Yctx (cross track) --- +-------------------+ ^ 5000 pixels/line | | ~5.73 degrees | |<----------------->| | | Boresight (+Zctx axis) is into the page This diagram illustrates the CCD center based pixel scheme used in USGS ISIS 3 camera model ([5]): ^ | direction of | flight | ^ +Xctx (along track) | | | | ~0.001146 degrees | | | v Pixel -2499.5 | Pixel 2499.5 --- +---------|---------+ | 1 line | 0 x-------------> +Yctx (cross track) --- +-------------------+ ^ 5000 pixels/line | | ~5.73 degrees | |<----------------->| | | Boresight (+Zctx axis) is into the page Optical Parameters -------------------------------------------------------- The following CTX nominal first order optical parameters are included in the data section below, from [4]: ----------------------------------------------------------------- Parameter ----------------------------------------------------------------- Focal Length, mm 350.0 f/ratio 3.25 IFOV, rad/pixel Cross-track 0.00002 Along-track 0.00002 Field of view (deg) Cross-track 5.73 Along-track 0.001146 ----------------------------------------------------------------- The keywords below provide nominal values from the table above. Angular size values in the keywords are given radians, with the cross-track size being the first value and the along-track size being the second value in each pair. The nominal focal length is omitted from this set because an updated value for it included in [5] is provided later in this file. \begindata INS-74021_F/RATIO = ( 3.25 ) INS-74021_FOV_ANGULAR_SIZE = ( 5.73, 0.001146 ) INS-74021_IFOV = ( 0.00002, 0.00002 ) \begintext Detector Parameters -------------------------------------------------------- The nominal CTX detector parameters from [4] are: ----------------------------------------------------------------- Parameter ----------------------------------------------------------------- Detector Array Size Cross-track 5000 Along-track 1 Detector Array Center Cross-track 2500.5 Along-track 0.5 Pixel Size, microns Cross-track 7 Along-track 7 ----------------------------------------------------------------- The values are given in millimeters for PIXEL_SIZE keywords and in counts for PIXEL_SAMPLES, PIXEL_LINES, and CENTER keywords. \begindata INS-74021_PIXEL_SIZE = ( 0.007, 0.007 ) INS-74021_PIXEL_SAMPLES = ( 5000 ) INS-74021_PIXEL_LINES = ( 1 ) INS-74021_CCD_CENTER = ( 2500.5, 0.5 ) \begintext FOV Definition --------------------------------------------------------------------------- This section contains definitions for the CTX FOV. These definitions are provided in the format required by the SPICE (CSPICE) function GETFOV (getfov_c). The set of assignments in the data section below defines the CTX FOV with respect to the CTX instrument frame to be a rectangles with the corners defined by the first and last pixels of CCD line array and the boresight along the +Z axis. This FOV definition uses angular extent style specification with the cross and along track angular sizes taken from the ``Optics Parameters'' section above. \begindata INS-74021_FOV_FRAME = 'MRO_CTX' INS-74021_FOV_SHAPE = 'RECTANGLE' INS-74021_BORESIGHT = ( 0.000000 0.000000 1.000000 ) INS-74021_FOV_CLASS_SPEC = 'ANGLES' INS-74021_FOV_REF_VECTOR = ( 0.000000 1.000000 0.000000 ) INS-74021_FOV_REF_ANGLE = ( 2.86478898 ) INS-74021_FOV_CROSS_ANGLE = ( 0.00057296 ) INS-74021_FOV_ANGLE_UNITS = 'DEGREES' \begintext Optical Distortion -------------------------------------------------------- See ``mroctxAddendum005.ti'' below. Platform ID --------------------------------------------------------------------------- This number is the NAIF instrument ID of the platform on which the instrument is mounted. CTX is mounted on the spacecraft bus. \begindata INS-74021_PLATFORM_ID = ( -74000 ) \begintext MROCTX Instrument Kernel ``mroctxAddendum005.ti'' ============================================================= This instrument kernel (I-kernel) contains parameters that describe the Mars Reconnaissance Orbiter CTX instrument model used by UGSG's ISIS 3. This model is defined with respect to the MRO_CTX frame. ``mroctxAddendum005.ti'' Version and Date ------------------------------------------------------------- Version 1.0 -- December 12, 2006 -- Elizabeth Miller, USGS, Flagstaff, AZ Initial version. Version 2.0 -- February 13, 2008 -- Steven Lambright, USGS, Flagstaff, AZ Added BORESIGHT keywords Version 3.0 -- February 21, 2008 -- Steven Lambright, USGS, Flagstaff, AZ Corrected the OD_K keyword Version 4.0 -- Mar 23, 2010 -- Debbie A. Cook, USGS, Flagstaff, AZ Update to include CK_FRAME_ID and CK_REFERENCE_ID Version 5.0 -- Apr 17, 2012 -- Annie HKraus, USGS, Flagstaff, AZ Updated FOCAL_LENGTH, OD_K, BORESIGHT_SAMPLE and BORESIGHT_LINE based on inflight calibration by Orrin Thomas and Randy Kirk. This involved tiepointing 6 overlapping CTX images to a HRSC orthoimage/DTM dataset in Gale crater and fitting the center and coefficients of a radial distortion polynomial. The focal length was then adjusted to its "calibrated" value which results in equal and opposite positive/negative excursions of the distortion polynomial over the field of view. Note also that the earlier versions of this kernel contained a sign error for all OD_K distortion coefficients, causing the use of the polynomial to double rather than remove the distortion. ``mroctxAddendum005.ti'' Data ------------------------------------------------------------- The following is the focal length, which is expressed in MILLIMETERS. This value comes from Randy Kirk's spreadsheet (2012) presenting the results of Orrin Thomas's inflight calibration of CTX based on comparison of 6 CTX images (3 adjacent stereopairs) to an HRSC orthoimage and DTM in Gale crater. CTX-HRSC tiepoints were measured and then projected into the CTX images with the focal length set to a nominal value and the distortion model temporarily to zero. This allowed straightforward fitting of a new radial distortion polynomial. Finally, the focal length was adjusted to its so-called calibrated value. The first distortion coefficient is varied at the same time so that the overall geometric model is unchanged, but at the calibrated focal length the overall distortion polynomial has equal and opposite positive and negative excursions over the field of view. The boresight samples and lines are used to specify the center of the detector device. There are two methods to specify the center of the detector array. The BORESIGHT parameters are expressed in pixels. \begindata INS-74021_FOCAL_LENGTH = 352.9271664 INS-74021_BORESIGHT_SAMPLE = 2543.46099 INS-74021_BORESIGHT_LINE = 0.430442527 \begintext The following is the pixel pitch, which is the distance between adjacent pixels on the CCD arrays. This is expressed in MILLIMETERS per pixel. \begindata INS-74021_PIXEL_PITCH = 7.0E-3 \begintext The following are the optical distortion parameters. These are used to transform from observed (distorted) coordinates (unprimed, e.g., x) to ideal coordinates (primed, e.g., xp). Both sets of coordinates are expressed in millimeters. r=sqrt(x^2 + y^2) dr = k0*r + k1*r3 + k2*r^5 rp = r - dr xp = x * (rp/r), similarly for yp or, rearranging a bit, we have a more efficient version: r^2 = x^2 + y^2 dr/r = k0 + r^2*(k1 + r^2*k2) xp = x - (dr/r)*x yp = y - (dr/r)*y The optical distortion parameters below come from Randy Kirk's spreadsheet (2012 inflight calibration). Note that the sign of the leading terms is opposite that in the previous versions of this kernel. Earlier kernels had mistakenly negated the distortion coefficients. As a result, their use in the formulae given above doubled rather than removing the optical distortion. \begindata INS-74021_OD_K = ( -0.00734339259200545000000, 0.00002837587863624170000, 0.00000001284198912402710 ) \begintext The following are the parameters for computing focal plane coords from CCD coords. x = transx[0] + transx[1]*ccdSample_c + transx[2]*ccdLine_c y = transy[0] + transy[1]*ccdSample_c + transy[2]*ccdLine_c \begindata INS-74021_TRANSX=( 0.0, 0.0, 0.007) INS-74021_TRANSY=( 0.0, 0.007, 0.0) \begintext Parameters for computing CCD coords from focal plane coords \begindata INS-74021_ITRANSS=( 0.0, 0.0, 142.85714285714) INS-74021_ITRANSL=( 0.0, 142.85714285714, 0.0) \begintext These are the parameters for writing c-kernels. Isis will create ck with the same frame endpoints as the mission ck. For Hirise the ck instrument frame is MRO_SPACECRAFT (-74000) and the ck reference frame is MRO_MME_OF_DATE (-74900). \begindata INS-74021_CK_FRAME_ID=-74000 INS-74021_CK_REFERENCE_ID=-74900 \begintext End of IK file.