Data Set Overview
  =================
 
    This data set contains derived data products for the MSL Hazard Avoidance
    cameras to support rover traverse planning, post-traverse assessment,
    rover localization, operation of the robotic arm, and the selection of
    science targets. The proximity of the Hazcams to the Martian surface
    allows close-up views of the fine-grain texture of materials in the
    immediate vicinity of the rover. Hazcam image data provides views of the
    surface not viewable by the cameras mounted on the Remote Sensing Mast.
    This data set is similar to the reduced data sets for the Hazard
    Avoidance cameras on MER [MAKIETAL2003].
 
    Detailed descriptions of all Reduced Data Record (RDR) products are
    available in the MSL_CAMERA_SIS.PDF, located in the DOCUMENT directory of
    this volume.
 
  Processing
  =========
 
    This data set uses the Committee on Data Management and Computation
    (CODMAC) data level numbering system. The MSL Hazcam RDRs are considered
    CODMAC Level 3 (calibrated data equivalent to NASA Level 1A), CODMAC
    Level 4 (resampled data equivalent to NASA Level 1B), or CODMAC Level 5
    (derived data equivalent to NASA level 3). The RDRs are derived from the
    Hazcam EDR data set and include  radiometrically corrected and/or camera
    model corrected and/or geometrically altered versions of the raw camera
    data, in single frame form. All of the RDR data products in this dataset
    have detached PDS labels.
 
 
  Data
  ====
 
    There are dozens of types of RDR products, described in detail in
    Section 5.1 of the MSL_CAMERA_SIS.PDF.  Below are descriptions of the
    most commonly used RDRs.
 
 
    1) Geometrically Corrected (Linearized) Images
 
    EDRs and single-frame RDRs are described by a camera model. This
    model, represented by a set of vectors and numbers, permit a point
    in space to be traced into the image plane, and vice-versa.
 
    EDR camera models are derived by acquiring images of a calibration
    target with known geometry at a fixed azimuth/elevation. The vectors
    representing the model are derived from analysis of this imagery.
    These vectors are then translated and rotated based on the actual
    pointing of the camera to represent the conditions of each specific
    image. The results are the camera model for the EDR.
 
    The Navcams use a CAHVOR model, while the Hazcams use a
    more general CAHVORE model. Neither are linear and involve some
    complex calculations to transform line/sample points in the image
    plane to XYZ positions in the scene. To simplify this, the images
    are warped, or reprojected, such that they can be described by a
    linear CAHV model. This linearization process has several benefits:
 
      a) It removes geometric distortions inherent in the camera
         instruments, with the result that straight lines in the scene are
         straight in the image.
 
      b) It aligns the images for stereo viewing. Matching points are on
         the same image line in both left and right images, and both left
         and right models point in the same direction.
 
      c) It facilitates correlation, allowing the use of 1-D correlators.
 
      d) It simplifies the math involved in using the camera model.
 
    Transformation introduces some artifacts in terms of scale change
    and/or omitted data (see the references). The linearized CAHV camera
    model is derived from the EDR's camera model by considering both the
    left and right eye models and constructing a pair of matched linear
    CAHV models that conform to the above criteria.
 
    The image is then projected, or warped, from the CAHVOR/CAHVORE
    model to the CAHV model. This involves projecting each pixel through
    the EDR camera model into space, intersecting it with a surface
    (which matters only for Hazcams and is a sphere centered on the
    camera), and projecting the pixel back through the CAHV model into
    the output image.
 
    See GEOMETRIC_CM.TXT for additional detail.
 
 
    2) Inverse Lookup Table Scaled Products
 
    If the Hazcam EDR is in 8-bit format as a result of onboard 12 to
    8-bit scaling using a Lookup Table (LUT), then an Inverse LUT is
    applied to rescale the 8 lowest bits into the 12 lowest bits in the
    16-bit signed integer.
 
 
    3) Radiometrically Corrected Products
 
    There are three types of radiometrically corrected products, and
    multiple methods of performing radiometric correction.  For more
    information, see the MSL_CAMERA_SIS.PDF in the DOCUMENT directory
    of this volume.
 
     a) RA products have been corrected to absolute radiance units of
        W/m^2/nm/steradian.
 
     b) RI products have been corrected for instrument effects only,
        and are in units of DN.
 
     c) IO products are radiance factor (I/F) and are dimensionless.
 
 
    4) Disparity Files
 
    A Disparity file contains 2 bands of 32-bit floating point numbers
    in the Band Sequential order (line, sample). Alternatively, line and
    sample may be stored in separate single-band files. The parallax, or
    difference measured in pixels, between an object location in two
    individual images (typically the left and right images of a stereo
    pair) is also called the disparity. Disparity files contain these
    disparity values in both the line and sample dimension for each
    pixel in the reference image. This reference image is traditionally
    the left image of a stereo pair, but could be the right image for
    special products. The geometry of the Disparity image is the same as
    the geometry of the reference image. This means that for any pixel
    in the reference image the disparity of the viewed point can be
    obtained from the same pixel location in the Disparity image.
 
    The values in a Disparity image are the 1-based coordinates of the
    corresponding point in the non-reference image. Thus, the coordinates
    in the reference image are the same as the coordinates in the
    Disparity image, and the matching coordinates in the stereo partner
    image are the values is the Disparity image. Disparity values of 0.0
    indicate no valid disparity exists, for example due to lack of
    overlap or correlation failure. This value is reflected in the
    MISSING_CONSTANT keyword.
 
 
    5) XYZ Products
 
    An XYZ file contains 3 bands of 32-bit floating point numbers in
    the Band Sequential order. Alternatively, X, Y and Z may be
    stored in separate single-band files as a X Component RDR, Y
    Component RDR and Z Component RDR, respectively. The single
    component RDRs are implicitly the same as the XYZ file, which is
    described below. XYZ locations in all coordinate frames for MSL
    are expressed in meters unless otherwise noted.
 
    The pixels in an XYZ image are coordinates in 3-D space of the
    corresponding pixel in the reference image. This reference image
    is traditionally the left image of a stereo pair, but could be
    the right image for special products. The geometry of the XYZ
    image is the same as the geometry of the reference image. This
    means that for any pixel in the reference image the 3-D position
    of the viewed point can be obtained from the same pixel location
    in the XYZ image. The 3-D points can be referenced to any of the
    MSL coordinate systems (specified by DERIVED_IMAGE_PARAMS Group
    in the PDS label).
 
    Most XYZ images will contain holes, or pixels for which no XYZ
    value exists. These are caused by many factors such as
    differences in overlap and correlation failures. Holes are
    indicated by X, Y, and Z all having the same specific value.
    This value is defined by the MISSING_CONSTANT keyword in the
    IMAGE object. For the XYZ RDR, this value is (0.0,0.0,0.0),
    meaning that all three bands must be zero (if only one or two
    bands are zero, that does not indicate missing data).
 
 
    6) Range (Distance) Files
 
    A Range (distance) file contains 1 band of 32-bit floating point
    numbers. The pixels in a Range image represent Cartesian distances
    from a reference point (defined by the RANGE_ORIGIN_VECTOR keyword
    in the PDS label) to the XYZ position of each pixel. This reference
    point is normally the camera position as defined by the C point of
    the camera model. A Range image is derived from an XYZ image and
    shares the same pixel geometry and XYZ coordinate system. As with
    XYZ images, range images can contain holes, defined by
    MISSING_CONSTANT. For MSL, this value is 0.0.
 
 
    7) Surface Normal Files
 
    A Surface Normal (UVW) file contains 3 bands of 32-bit floating
    point numbers in the Band Sequential order. Alternatively, U, V and
    W may be stored in separate single-band files as a U Component RDR,
    V Component RDR and W Component RDR, respectively. The single
    component RDRs are implicitly the same as the UVW file.
 
    The pixels in a UVW image correspond to the pixels in an XYZ file,
    with the same image geometry.  However, the pixels are interpreted
    as a unit vector representing the normal to the surface at the point
    represented by the pixel. U contains the X component of the vector,
    V the Y component, and W the Z component. The vector is defined to
    point out of the surface (e.g. upwards for a flat ground). The unit
    vector can be referenced to any of the MSL coordinate systems
    (specified by the DERIVED_IMAGE_PARAMS Group in the PDS label).
 
    Most UVW images will contain holes, or pixels for which no UVW
    value exists. These are caused by many factors such as differences
    in overlap, correlation failures, and insufficient neighbors to
    compute a surface normal. Holes are indicated by U, V, and W all
    having the same specific value. Unlike XYZ, (0,0,0) is an invalid
    value for a UVW file, since they are defined to be unit vectors. Thus
    there is no issue with the MISSING_CONSTANT as there is with XYZ,
    where (0.0,0.0,0.0) is valid.
 
 
    8) Surface Roughness Maps
 
    The roughness maps contain surface roughness estimates at each pixel
    in the image, along with a 'goodness' flag indicating whether the
    roughness meets certain criteria.
 
    For each pixel, the surface normal product defines a reference plane.
    XYZ pixels in the area of interest are gathered, and the distance to
    the plane is computed. Minimum and maximum distances from the plane
    are computed, with outliers excluded.  Roughness is defined as the
    distance between this min and max.
 
 
    9) Slope Products
 
    The slope RDR products represent aspects of the slope of the terrain
    as determined by stereo imaging.  There are several slope types,
    described in further detail in the MSL_CAMERA_SIS.PDF.
 
 
    10) Arm Reachability Maps
 
    The Arm Reachability Maps contain information about whether or not the
    instruments on the arm can reach (either contact or image) the object or
    location represented by each pixel in the scene.  They are derived from
    the XYZ and Surface Normal products.
 
 
    11) Stereo Anaglyphs
 
    A stereo anaglyph is a method of displaying stereo imagery quickly
    and conveniently using conventional display technology (no special
    hardware) and red/blue glasses. This is done by displaying the left
    eye of the stereo pair in the red channel, and displaying the right
    eye in the green and blue channels. An anaglyph data product simply
    captures that into a single 3-band color image, which can be
    displayed using any standard image display program with no knowledge
    that it is a stereo image. The red (first) band contains the left
    eye image, while the green and blue (second and third) bands each
    contain the right eye image (so the right image is duplicated in
    the file).
 
    Anaglyphs are created manually from CAHV linearized Full Framed
    stereo pair EDRs or mosaics.  Often times the images are
    stretched prior to creating the anaglyph.  After stretching, the
    images are converted to a VICAR cube, which creates a single
    multi-band image. The final step involves adding the PDS label.
 
 
 
  Software
  ========
 
    Hazcam camera downlink processing software used by the science and
    engineering team during operations is focused on rapid reduction,
    calibration, and visualization of images in order to make
    discoveries, to accurately and expeditiously characterize the
    geologic environment around the rover, and to provide timely input
    for operational decisions concerning rover navigation and Robotic
    Arm target selection.
 
    Hazcam images can be viewed with the program NASAView, developed by
    the PDS and available for a variety of computer platforms from the
    PDS web site http://pds.nasa.gov/tools/nasa-view.shtml. There is
    no charge for NASAView.
 
 
  Media/Format
  ============
 
    The data set will be delivered and made available to the public
    through the Planetary Data System web sites.

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