Changes between Version 14 and Version 15 of Help/LeicaLidarDems


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Timestamp:
May 19, 2009 2:37:25 PM (10 years ago)
Author:
mark1
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  • Help/LeicaLidarDems

    v14 v15  
    5252where the map names are as before, the imported point cloud rasters, and lidar_mosaic is the output name for the single concatenated raster set.
    5353
    54 <center>[[Image(mosaic_with_holes.png,width=100)]]</center>
    5554
    56 <center>Figure: Mosaic of point cloud data gridded at 2m resolution. Holes (no data) are shown as white.</center>
     55[[Image(mosaic_with_holes.png,width=100)]]
     56{{{
     57#!html
     58<p style="text-align: center">Figure: Mosaic of point cloud data gridded at 2m resolution. Holes (no data) are shown as white</p>
     59}}}
     60
    5761
    5862Assuming that there are only small holes in the data set and the DEM is required only within the lidar swath coverage, we can use the `r.surf.idw` command to interpolate over the lidar. This command will also interpolate into the GRASS region where the LIDAR is undefined.
     
    6266where the output raster, lidar_mosaic_idw, has been interpolated using an inverse distance weighted formula. As well as filling in holes within the lidar swath, this will also interpolate over empty parts of the GRASS region, resulting in possibly unrealistic data values.
    6367
    64 <center>[[Image(interp_full_region.png,width=100)]]</center>
     68[[Image(interp_full_region.png,width=100)]]
     69{{{
     70#!html
     71<p style="text-align: center">Figure: Interpolated point cloud data over full GRASS region.</p>
     72}}}
    6573
    66 <center>Figure: Interpolated point cloud data over full GRASS region.</center>
    6774
    6875This can be improved if you wish by using a mask when interpolating the data. To create a mask, the easiest way is to use your input data at a low resolution. This creates a raster which covers the LIDAR swath but contains no holes in the data (assuming the resolution is selected low enough).  To import the data at a lower resolution , repeat steps 1-3 for each ASCII point cloud setting the `res` variable to a suitable value, e.g. 50.0 and outputting to a new map.  Then repeat steps 4 and 5 to create a raster covering the combined LIDAR swath.
     
    7784
    7885this results in a map where the internal holes have been filled, but the area outside the swath coverage remains unchanged.
     86
     87[[Image(interp_with_mask.png,width=100)]]
     88{{{
     89#!html
     90<p style="text-align: center">Figure: Interpolated point cloud data after implementing a mask.</p>
     91}}}
    7992
    8093To extend the coverage of your DEM, if required, it is suggested to patch on external DEM data. If you have access to a good quality DEM then use that, else the SRTM 3 arc second DEM is freely available and covers most of the globe between +-60 degrees latitude. To see how to make a DEM from SRTM data see the [wiki:Processing/SRTMDEMs SRTM DEM] page. Make sure to select the projection  the same as your LIDAR DEM.