Changes between Version 2 and Version 3 of PROJ4toCS-MAP


Ignore:
Timestamp:
Aug 12, 2008 4:26:59 PM (10 years ago)
Author:
hugueswski
Comment:

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  • PROJ4toCS-MAP

    v2 v3  
    13131497 PROJ4 systems mapped to a CS-Map "Custom System".[[BR]]
    141484   PROJ4 systems could not be mapped to any existing system or could not be used to generate a custom system, no conversion at all.[[BR]]
     15[[BR]]
     16Here is how the general WKT mapping code works:[[BR]]
     17- read the WKT and try to detect the flavor[[BR]]
     18- decode the WKT sub elements: system, datum, ellipsoid, unit, ...[[BR]]
     19- generate a complete CS-Map definition based on all the gathered sub elements.[[BR]]
     20- validate the definition. At this stage if we succeed, we could stop because we have a valid system we can work with[[BR]]
     21- use this valid definition and with the help of the WKT mapping file try to map each sub element with a CS-Map element from its dictionary files: ellipsoid name, datum name, coordinate system name[[BR]]
     22- return either the definition generated from the WKT or the CS-Map definition with the names from the CS-Map dictionaries[[BR]]
     23[[BR]]
     24For those 84 that failed, it can be the syntax of the WKT that comes from PROJ4, a unit that CS-Map doesn't know about ...[[BR]]
     25If I randomly pick up a failed system like CH1903 which WKT is:[[BR]]
     26[[BR]]
     27PROJCS["unnamed",[[BR]]
     28        GEOGCS["Bessel 1841",[[BR]]
     29                DATUM["unknown",[[BR]]
     30                        SPHEROID["bessel",6377397.155,299.1528128]],[[BR]]
     31                PRIMEM["Greenwich",0],[[BR]]
     32                UNIT["degree",0.0174532925199433]],[[BR]]
     33        PROJECTION["Hotine_Oblique_Mercator"],[[BR]]
     34        PARAMETER["latitude_of_center",46.9524055555767],[[BR]]
     35        PARAMETER["longitude_of_center",7.4395833333842],[[BR]]
     36        PARAMETER["azimuth",90],[[BR]]
     37        PARAMETER["rectified_grid_angle",90],[[BR]]
     38        PARAMETER["scale_factor",1],[[BR]]
     39        PARAMETER["false_easting",600000],[[BR]]
     40        PARAMETER["false_northing",200000]][[BR]]
     41[[BR]]
     42there is no unit for the PROJCS system. That must be why CS-Map fails to just decode the string and extract its sub elements.[[BR]]
     43That means we are not even be at the stage of trying to generate a full definition or even to map it to a CS-Map name.[[BR]]
     44Another random system "panama" shows the same problem, no unit is available in the WKT for PROJCS.[[BR]]
     45So, it looks like the syntax of the failed WKTs is the reason of the failure.[[BR]]
    1546
    1647=== 1636 PROJ4 systems mapped to CS-Map "Code" ===
     
    743774||EPSG:2767||Code||CAHP-II||
    744775||EPSG:2768||Code||CAHP-III||
     776
     777
    745778||EPSG:2769||Code||CAHP-IV||
    746779||EPSG:2770||Code||CAHP-V||
     
    818851||EPSG:2844||Code||TXHP-N||
    819852||EPSG:2845||Code||TXHP-NC||
     853
    820854
    821855
     
    10611095||EPSG:3213||Code||WGS84.SCAR-SQ43-44||
    10621096||EPSG:3214||Code||WGS84.SCAR-SQ45-46||
     1097
    10631098||EPSG:3215||Code||WGS84.SCAR-SQ47-48||
    10641099||EPSG:3216||Code||WGS84.SCAR-SQ49-50||