Shape Dataset Organization                            
                                                                              
This shape-model dataset includes a wide variety of shape models of comet     
67P/Churyumov-Gerasimenko.  They have been developed by several different     
groups, using data from several different portions of the Rosetta mission,    
using a variety of techniques, and intended for a variety of different        
purposes.  Several of these models have been cited in the literature as       
underlying various investigations.  The different shape models are collected  
together in order to make it easier for users to choose the appropriate       
model, but the wide variety means that there are many possible ways to        
organize the archive.                                                         
                                                                              
At the time this document is written (February 2016), only a few of the       
anticipated models have been archived (and some models have not yet even been 
created), but to understand the organization we discuss generically all the   
models that we hope will be archived.  All the shape models tesselate the     
surface of the nucleus into triangular, flat plates.  At the highest level,   
the datasets are separated into ascii formats and binary formats.  The binary 
formats are exclusively the Digital Shape Kernels that are used in SPICE      
(routines currently in beta-test version but expected to be in the general    
release in spring 2016).  The ascii versions are designed for non-SPICE users 
and for simple visualization of the geometry.  They always include an ascii   
version that follows the standard used in PDS-SBN for decades (long prior to  
the availability of DSK) that includes a wrapper that makes them viewable in  
any VRML-aware application, of which there are many available.                
                                                                              
At the next level, the models are divided into groups corresponding to the    
team that produced the models and the method that team used.  The four groups 
at this level are, as abbreviated in directory names and file names: 1)       
mspcd_lam, Modified StereoPhotoClinometry by Distortion, produced at the      
Laboratoire d’Astrophysique de Marseille, 2) spc_esa, StereoPhotoClinometry 
produced by the flight operations team of ESA (European Space Agency) and     
converted to standard formats by the Rosetta Mission Operations Center        
(RMOC), 3) spc_lam_psi, StereoPhotoClinometry produce by a collaboration      
between the Laboratoire d’Astrophysique de Marseille and the Planetary      
Science Institute, and 4) spg_dlr, StereoPhotoGranulometry produced at the    
German Aerospace Center (DLR) group in Berlin.  This grouping also separates  
the models by the instruments used to obtain the input images, the models     
from ESA having been derived entirely from the NAVCAMs (NAVCAM1 and NAVCAM2   
are nominally identical), whereas the other three groups are based entirely   
on the scientific cameras, OSIRIS-NAC and OSIRIS-WAC.  At this writing, there 
are currently no models available in group 4.  See other documents to         
understand the differences among the techniques.                              
                                                                              
At the third level, the models are sorted by the time period of the data      
used, which affects the geographic coverage of the data and the best spatial  
resolution achieved.  For the models from ESA, this is denoted by the last    
MTP (Medium Term Planning) cycle of the data, whereas for the models using    
the scientific cameras, the OSIRIS teams used sequential numbers to indicate  
the time period, with detail s given in the relevant subdirectories.  At this 
writing, the ESA models utilize data obtained through MTP09 (through          
mid-November 2014, i.e., data prior to the release of the Philae Lander).     
The OSIRIS models currently on hand are all SHAP2, using data only through 3  
August 2014.  Anticipated future deliveries include an SPG version of SHAP4,  
SPC and MSPCD versions of SHAP5, and TBD versions of SHAP7 (data being taken  
as this is written).                                                          
                                                                              
At the next level, because the full-resolution models are very large, there   
are models with various levels of reduced resolution available, intended for  
purposes that do not require the highest resolution and therefore speed up    
calculations.