Description of the Gaskell Phobos Shape Model bundle V1.0
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Bundle Generation Date: 2020-09-22
Peer Review: Neese_Richardson_Mueller_Migration
Discipline node: Small Bodies Node


Content description for the Gaskell Phobos Shape Model bundle
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Note: This bundle was migrated to PDS4 from the PDS3 data set VO1-SA-VISA/VISB-5-PHOBOSSHAPE-V1.0. For PDS3 data sets migrated to PDS4, the following text is taken verbatim from the data set description and confidence level note of the PDS3 data set catalog file. In these cases, some details may not be correct as a description of the PDS4 bundle.

This shape model of Phobos is based on 224 Viking Orbiter 1 VIS-A and VIS-B camera images taken in 1976-1978, and eight Phobos 2 VSK images taken in 1989. The shape model was prepared by Robert Gaskell on March 11, 2006.                                                                     
                                                                              
The geometrical coordinate system of this model is defined by the planetary constants file pck00006.tpc, available in PDS from the NAIF node.  To find the file in PDS, go to the NAIF SPICE archive at https://naif.jpl.nasa.gov/naif/data_pds_archived.html.  At the top of the page, click 'PDS SPICE Archives'.  In the table of data links, select the 'link' for the Viking Orbiter mission. Within the volume, go to the data/pck directory, and download the desired file (pck00006.tpc).                                                      
                                                                              
The parameters of the model are as follows:                                   
                                                                              
    Number of landmarks: 456                                                  
    Formal position uncertainty: 18 m/component                               
    Number of images: 232                                                     
    Pointing uncertainty: .018 mrad                                           
    S/C position uncertainty: N/A (positions treated as given)                
    Pointing residuals: (initial pointings treated as unknown)                
    range residuals N/A                                                       
    Number of measurement pairs: 18345                                        
    Number of measurements per landmark: 40                                   
    RMS LMK location residual: 25 m/component                                 
                                                                              
 The models were originally prepared in the Implicitly Connected Quadrilateral (ICQ) format.  Vertex-facet format versions, derived from the ICQ versions, are also provided.  The filenames are phobos_quad512q.tab and phobos_ver512q.tab, where 512 is the value of Q (an indicator of the resolution). Files with three selections of lower resolution are also provided for each format, with similar filenames but lower values of Q.                                                        
                                                                              
The file 'phobosimagelist.tab' is a list of the Viking Orbiter 1 VIS-A and VIS-B camera images and Phobos 2 VSK-FREGAT images used to generate this model.  (VSK-FREGAT is a three-channel television camera which flew on the Soviet Phobos 2 mission.)                                                 
                                                                              
 A text file, 'icqmodel.txt' is provided in the 'document' directory which describes the ICQ format and the derivation of the vertex-facet versions.


Caveats to the data user
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Note that the vertex-facet versions of the model have some duplicate vertices on the edges and corners of the cube.  The duplicate vertices are not used in the facet table, resulting in the presence of some vertices in the vertex table which do not appear in the facet table.  This does not  affect the correctness of the vertex-facet version.