Specify sampling method for a new grid?

tjhbtjhb Global Mapper UserPosts: 454Trusted User
edited November 2010 in Technical Support
Is there a way, directly after executing a GENERATE_GRID_FILE command, to specify the sampling method to be used for the new gridded layer?—I'd like to specify bicubic resampling during the following EXPORT_ELEVATION* operation, which involves cropping exactly to a specific AOI.

A workaround would be to export the DEM without cropping (so no interpolation), unload it and reload it (specifying SAMPLING_METHOD at this point), then export a second time with cropping to the AOI. Is that necessary?

[*There doesn't seem to be a way of specifying the sampling method explicitly for the EXPORT_ELEVATION command itself.]

Comments

  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited November 2010
    I have updated the GENERATE_ELEV_GRID command to support the display option parameters (like for the sample method) that the IMPORT command support, so you can now specify the sampling method to use when generating the grid layer. I have placed a new build at http://www.globalmapper.com/global_mapper12.zip with the change for you to try. Simply download that file and extract the contents into your existing v12.xx installation folder to give it a try. If you are using the 64-bit v12 version there is a new build at http://www.globalmapper.com/global_mapper12_64bit.zip .

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • tjhbtjhb Global Mapper User Posts: 454Trusted User
    edited November 2010
    Crikey that's a welcome surprise. I'll test it right away.

    (I got the name of GENERATE_ELEV_GRID very wrong. I seem to have been making a lot of mistakes here lately. On this occasion my excuse is that it's Friday evening here.)

    Thanks.
  • tjhbtjhb Global Mapper User Posts: 454Trusted User
    edited November 2010
    Mike I don't think this is working as expected. The two scripts shown below produce indistinguishable output.

    In any case, can I also ask if it would be possible to make the EXPORT_ELEVATION routine implement the value of the GUI setting "Terrain Export: Specify Bounds as Pixel is Area" during export? Currently it seems to use Pixel is Point always.

    (It would perhaps be better if EXPORT_ELEVATION had its own ad hoc parameter for the pixel model, but adopting the GUI setting would be enough. Not many people need to change it.)

    Script 1, creating a DEM at 2 metres per pixel, applying the bicubic sampling method, then exporting at 0.5 metres:
    GLOBAL_MAPPER_SCRIPT VERSION=1.00

    UNLOAD_ALL

    SET_LOG_FILE \
    FILENAME="E:\{Output}\GM log.txt"

    DEFINE_PROJ \
    PROJ_NAME="NZTM2000_NZGD2000"
    Projection New Zealand Transverse Mercator 2000
    Datum NZGD_2000
    Zunits NO
    Units METERS
    Xshift 0.000000
    Yshift 0.000000
    Parameters
    END_DEFINE_PROJ

    LOAD_PROJECTION \
    PROJ_NAME="NZTM2000_NZGD2000"

    DIR_LOOP_START \
    DIRECTORY="D:\{Input}\SHP\" FILENAME_MASKS="*.SHP" \
    RECURSE_DIR=NO

    IMPORT \
    FILENAME="%FNAME_W_DIR%" TYPE=SHAPEFILE \
    PROJ_NAME="NZTM2000_NZGD2000"

    GENERATE_ELEV_GRID \
    ELEV_UNITS=METERS \
    SPATIAL_RES=2.0,2.0 \
    NO_DATA_DIST_MULT=50 \
    LAYER_DESC="DEM %FNAME_WO_EXT%" \
    SAMPLING_METHOD=BICUBIC

    EXPORT_ELEVATION \
    FILENAME="E:\{Output}\DEM %FNAME_WO_EXT%.flt" \
    TYPE=FLOATGRID \
    ELEV_UNITS=METERS \
    POLYGON_CROP_FILE="D:\{Input}\AOI\%FNAME_WO_EXT%.shp" \
    POLYGON_CROP_BBOX_ONLY=NO \
    POLYGON_CROP_USE_ALL=YES \
    SPATIAL_RES=0.5,0.5 \
    FORCE_SQUARE_PIXELS=YES

    UNLOAD_LAYER FILENAME="%FNAME%"

    DIR_LOOP_END
    Script 2, identical except for the line
    SAMPLING_METHOD=NEAREST_NEIGHBOR
  • tjhbtjhb Global Mapper User Posts: 454Trusted User
    edited November 2010
    Specifying SAMPLING_METHOD=BICUBIC makes no difference either.
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited November 2010
    I tried this myself and found a problem that was preventing the SAMPLING_METHOD parameter from working right for GENERATE_ELEV_GRID. That is now fixed. I have placed a new build at http://www.globalmapper.com/global_mapper12.zip with the change for you to try. Simply download that file and extract the contents into your existing v12.xx installation folder to give it a try. If you are using the 64-bit v12 version there is a new build at http://www.globalmapper.com/global_mapper12_64bit.zip .

    I also updated the export bounds for the EXPORT_ELEVATION script command to be treated as 'pixel is area' if the option to treat elevation bounds that was is checked in the Advanced section of the General tab of the Configuration dialog.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • tjhbtjhb Global Mapper User Posts: 454Trusted User
    edited November 2010
    That looks perfect to me, on both counts.

    Thank you very much again Mike.

    Tim
  • tjhbtjhb Global Mapper User Posts: 454Trusted User
    edited November 2010
    I thought I should say what I was trying to do, that has been made possible by these changes.

    The input data was LiDAR points, very finely spaced, covering an area about 80km vertically, and about 5km horizontally at any point.

    The LiDAR data was supplied in discrete tiles. If I used GM to make DEMs for each tile (or groups of tiles), then there were ridges or gaps at tile boundaries. (Rightly so.)

    If I tried to make a single DEM from all tiles combined, then the memory required was prohibitive. (With 12 GB of physical RAM, Windows 7 64-bit could not cope, despite effectively unlimited swap file space.)

    The answer was to make overlapping sets of points, create a DEM from each set, then crop each DEM to its net area, removing the overlap (and with it any edge effect).

    To get maximum data fidelity, I needed minimal displacement between DEM pixels as they were created, and after cropping to their net tile area.

    The changes above have enabled this workflow.

    I don't think I've explained it at all well. Here is my final GM script (unfortunately in italics and without meaningful indentation).
    GLOBAL_MAPPER_SCRIPT VERSION=1.00

    UNLOAD_ALL

    SET_LOG_FILE \
    FILENAME="E:\{Output}\GM log.txt"

    DEFINE_PROJ \
    PROJ_NAME="NZTM2000_NZGD2000"
    Projection New Zealand Transverse Mercator 2000
    Datum NZGD_2000
    Zunits NO
    Units METERS
    Xshift 0.000000
    Yshift 0.000000
    Parameters
    END_DEFINE_PROJ

    LOAD_PROJECTION \
    PROJ_NAME="NZTM2000_NZGD2000"

    DIR_LOOP_START \
    DIRECTORY="D:\{Input}\SHP\" FILENAME_MASKS="*.SHP" \
    RECURSE_DIR=NO

    IMPORT \
    FILENAME="%FNAME_W_DIR%" TYPE=SHAPEFILE \
    PROJ_NAME="NZTM2000_NZGD2000"

    GENERATE_ELEV_GRID \
    ELEV_UNITS=METERS \
    SPATIAL_RES=0.5,0.5 \
    NO_DATA_DIST_MULT=250 \
    LAYER_DESC="DEM %FNAME%" \
    SAMPLING_METHOD=BICUBIC

    EXPORT_ELEVATION \
    FILENAME="E:\{Output}\DEM %FNAME_WO_EXT%.flt" \
    TYPE=FLOATGRID \
    ELEV_UNITS=METERS \
    POLYGON_CROP_FILE="D:\{Input}\AOI\%FNAME_WO_EXT%.shp" \
    POLYGON_CROP_BBOX_ONLY=NO \
    POLYGON_CROP_USE_ALL=YES \
    SPATIAL_RES=0.5,0.5 \
    FORCE_SQUARE_PIXELS=YES

    UNLOAD_ALL

    DIR_LOOP_END
  • bernnadette03bernnadette03 Global Mapper User Posts: 1
    edited November 2010
    i relly like this site
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