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Global mapper grid file

kartoone76kartoone76 Global Mapper UserPosts: 38Trusted User ✭✭
edited March 2008 in Elevation Data
Is there a way to extract the bounding coordinates from a global mapper grid (GMG) file? It appears to be a binary file and a quick scan of the file didn't reveal anything that would hint at the location of where the bounding coordinates would be. Is there a specific byte location or does the entire file have to be parsed in order to find out the bounding coordinates?

As an alternative, I am prepared to write a script that would use the EXPORT_METADATA command to export the metadata (which I presume would include the bounding coordinates) for all loaded GMG files and then create a separate non-global mapper script to re-process the exported .txt file to extract the bounding coordinates. I was just wondering if there is an easier way.



  • global_mapperglobal_mapper Administrator Posts: 17,238BMG Staff ✭✭✭
    edited March 2008
    It is a binary file. Here is the C declaration of the header from which you can extract the bounding box:

    struct PackedHeader_t
    sint32 mHeaderSize; // Size of entire header
    uint32 mMagicNumber; // Magic number
    double mMinX; // X coordinate of center of top left sample
    double mMaxY; // Y coordinate of center of top left sample
    double mPixelSizeX; // Ground size of a pixel in the X direction
    double mPixelSizeY; // Ground size of a pixel in the Y direction
    sint32 mImageWidth; // Total number of valid pixels in a row
    sint32 mImageHeight; // Total number of valid pixels in a column
    uint8 mTilePowerX; // 1 << Total number of samples in a tile row
    uint8 mTilePowerY; // 1 << Total number of samples in a tile column
    sint8 mElevUnits; // Elevation units (same as ViewerUtils)
    sint32 mMinZ; // Minimum elevation
    sint32 mMaxZ; // Maximum elevation

    // Offsets to tables and other values
    uint32 mProjOffset; // Offset to embedded projection string
    uint32 mProjSize; // Size of embedded projection string
    uint32 mLayerTableOffset; // Offset to layer table
    uint32 mLayerTableSize; // Size of layer table
    uint32 mLayerTableRecSize; // Size of layer table record
    uint32 mTileSizeTableOffset; // Offset to table of tile sizes
    uint32 mTileSizeTableRecSize; // Size of tile size table record
    uint32 mTileTableOffset; // Offset to the tile data table

    Let me know if I can be of further assistance.


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