Data Set Overview
    =================
       This data set presents digital elevation maps (DEM) of the portions
       of the surface of the nucleus of comet 19P/Borrelly that were
       illuminated and visible during the Deep Space 1 encounter.  During
       the approach to the nucleus, the spacecraft executed a turn to keep
       the body-mounted camera oriented on the target.  In combination with
       this turn, the changing viewing geometry allows subsequent images to
       be associated into stereo pairs, from which valuable information can
       be extracted about the three-dimensional structure of the nucleus.
 
       The maps were separately created by members of the US Geological
       Survey (USGS) and by the German Aerospace Center (Deutschen Zentrum
       fur Luft- und Raumfahrt - DLR) using a series of three of the best
       available images taken by the Miniature Integrated Camera and
       Spectrometer (MICAS) aboard the Deep Space 1 spacecraft as it flew
       by the comet nucleus.  The elevations were derived by using parallax
       measurements between two pairs of images to determine elevation
       above a reference plane.  The unit surface normal vector was also
       calculated for the USGS model.  Descriptions of the stereo analysis
       procedure are provided in Soderblom, et al. (2002)
       [SODERBLOMETAL2002], Kirk, et al. (2004) [KIRKETAL2004] for the USGS
       model and Oberst et al. (2004) [OBERSTETAL2004] for the DLR model.
 
       Kirk, et al. (2004), note that:
          Elevations relative to an arbitrary zero (approximately the
          lowest point on the limb) range to approximately 4600 m, with
          only a small area above 4000 m.  There is a trend from low
          areas at the 'top' end of the nucleus ... to areas higher than
          3000 m at the 'bottom' end.  Hence, the bottom of the nucleus
          appears to be tilted toward the camera.
 
       'Top' and 'bottom', as referenced above, are with respect to the
       images as published in Kirk, et al. (2004).  In these images the
       elongated nucleus is presented with the narrower end in the lower
       left corner.
 
       A comparison of the two models, which are derived from the same
       data, but use different techniques to derive the elevations, provide
       an estimate of the uncertainties in the elevation.  Although the
       differences vary with position on the nucleus, the mean error is
       about 85 m.
 
 
    Parameters
    ==========
       The DEM data are presented in individual ASCII files (one each for
       the USGS and DLR models) listing X, Y and Z coordinates for the grid
       points.  The USGS model also provides the corresponding Nx, Ny, and
       Nz elements of the unit surface normal vector at each point.
 
    Processing
    ==========
       The three highest-resolution images, identified in the PDS data
       set DS1-C-MICAS-3-EDR-VISCCD-BORRELLY-V1.0 as CCD_MID_5_3,
       CCD_MID_5_4, and CCD_NEAR_01, were used to generate the
       elevation map.  (Copies of these three images are included in
       the data/images directory for this data set).  A description of
       the image processing and calibration can be found in Soderblom
       et al. (2002) [SODERBLOMETAL2002] and Oberst et al. (2000)
       [OBERSTETAL2000].
 
       The CCD_MID_5_3 / CCD_NEAR_01 stereo pair was used for the standard
       topographic models, while the CCD_MID_5_4 / CCD_NEAR_01 pair was
       used to derive separate models in order to check for consistency.
       The details of converting the stereoscopic data into an elevation
       model are described in Kirk, et al. (2004) [KIRKETAL2004] for the
       USGS model and Oberst et al. (2004) [OBERSTETAL2004] for the DLR
       model.
 
       The USGS data were received at the SBN as a series of six
       two-dimensional arrays of numbers (in ASCII text).  Each of these
       source files contained the value for a single coordinate or vector
       element (X, Y, Z, Nx, Ny, Nz).  SBN personnel combined the
       corresponding coordinates and elements from these files into the
       single table presented here, discarding null values and sorting on
       increasing X and Y.
 
    Coordinate System
    =================
       Because only one side of the comet nucleus was observed, the X-Y
       coordinate system used for these data was a local space rectangular
       system defined by the investigators.  The elevation (Z) is defined
       with respect to a reference plane that is roughly in the plane of
       the sky.  Details regarding the coordinates used in the two models
       are given in the COORDS.TXT file in the documents directory.
 
       The solar phase angle relating to the image was 51.624 degrees, so
       the Sun was 39.376 degrees out of the plane of the image, with a
       clock angle of 265.116 degrees.
 
       SBN personnel noted that there are some negative Z values, located
       mainly near the image limb.
 
 
    Media/Format
    ============
       This data set is available for electronic download.
 
    Author
    ======
       Unless otherwise noted, the text in this file was prepared by Tony
       Farnham and Ed Grayzeck, Small Bodies Node.

Confidence Level Overview
    =========================
       No smoothing has been applied to these models, and depending on the
       use, it is recommended that users employ some form of smoothing to
       suppress the noise in the data set.
 
    Review
    ======
       The USGS data set were reviewed in October 2003, and the DLR data
       were reviewed in May 2004.