Global Mapper v25.0

Lidar data -create elevation GRID

irenegobran
irenegobran Global Mapper UserTrusted User
edited July 2014 in Technical Support
Hi,
i have a big lidar data project and I need to create asci files for ground class. in order not to have problems between tiles boundary related to interpolation differences in empty area,i would prefer to create mosaics with overlap and then cut them,i need to know the capacity of GLOBAl Mapper lidar module to create grid ,i tried with a lot of files but it is crashed . What is the limite of memory of GM to organise the size of my tiles according .Is there another way to do elevation grid for tiles without having problems between boundaries.
Thanks!

Comments

  • global_mapper
    global_mapper Administrator
    edited June 2014
    I would suggest using File->Create New Map Catalog to create a map catalog of your Lidar tiles, then use the Analysis menu command to grid the data and use the Tiling tab to split up the operation in to smaller pieces. This will automatically overlap around the edges when getting the points to grid, but actually cut the resulting grid to the specified bounds. This allows seamlessly gridding large amounts of data.

    You can also choose to export the grids directly to a GMG file rather than keeping them all in memory. Note the Lidar module binned gridding will be much faster than the traditional TIN-based gridding and also use a lot less memory when there are a large number of points.

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation
  • irenegobran
    irenegobran Global Mapper User Trusted User
    edited July 2014
    Thanks for the answer,I have tested what you propose,it is really quick but we still can see tiles boundaries in the data set (see attached file)
  • global_mapper
    global_mapper Administrator
    edited July 2014
    Those boundaries are visual artifacts because by default hill shading and interpolation stop at layer edges, so you will get slightly different shading on layer edges, particularly in hilly areas, since the adjacent sample for the shadow angle is in a different layer and not available. If you add all of your grid files to a map catalog they should then be known as "sibling" layers so the shading and interpolation can cross the boundary.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation
  • irenegobran
    irenegobran Global Mapper User Trusted User
    edited July 2014
    This is exactly what I have done for calculation ,I have openned all my xyz files in map catalog and then used the analysis -creat grid with using a tile index to export my tiles with activating the option export to global mapper format,and then batch convert-export to change from global mapper format to arc asci grid format . it seems that even with using all tiles in map catalog for calculation,i still have this problem ,or do you mean to display the tiles ,i should open them in map catalog? or may be for the format change ,i should use also map catalog from global mapper format to arc asci grid?
  • irenegobran
    irenegobran Global Mapper User Trusted User
    edited July 2014
    could it be the option "fill entire bounding box instead of just inside convex hull? that is missing to have seamless interpolation
  • global_mapper
    global_mapper Administrator
    edited July 2014
    I mean to display the tiles you need to add them to a map catalog. The seams aren't really seams in the data, just a visual discontinuity caused by the shadowing and interpolation not going across layer boundaries in normal circumstances.

    The option to 'fill entire bounding box instead of convex hull' only applies to TIN-based gridding and not the Lidar grid modes. It shouldn't be needed in this case.

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation