use of option '-use_bb' with lasgrid

[Martin Isenburg]

Hello,

lasgrid will by default make the generated rasters only as big as there are filled grid cells and thereby make the raster bounding box as small as possible. The option '-use_bb' assures that the resulting raster uses the full bounding box of the input - whether there are filled grid cells or not.

I had a question of why the reuslting merged ASC raster was not "square" after merging a four (a 2 by 2 grid of) existing ASC rasters. The tool lasgrid reads those ASC rasters via on-the-fly conversion of grid cells to LAS points and then creates a grid with the tightest possible bounding box as output. If you want to use the *full* bounding box with all the empty space included you need to add the '-use_bb' parameter. See the bounding boxes of the four example ASC rasters and the two possible ways of merging them with lasgrid below:

 

D:\LAStools\bin>more DGMWA001_323925899.asc

ncols           1000

nrows           1000

xllcorner       392000.00

yllcorner       5899000.00

cellsize        1.00

NODATA_value    -9999.00

-9999.00 -9999.00 -9999.00 -9999.00 -9999.00 [...]

D:\LAStools\bin>more DGMWA001_323925900.asc

ncols           1000

nrows           1000

xllcorner       392000.00

yllcorner       5900000.00

cellsize        1.00

NODATA_value    -9999.00

-9999.00 -9999.00 -9999.00 -9999.00 -9999.00 [...]

D:\LAStools\bin>more DGMWA001_323935899.asc

ncols           1000

nrows           1000

xllcorner       393000.00

yllcorner       5899000.00

cellsize        1.00

NODATA_value    -9999.00

-6.87 -6.80 -6.72 -6.64 -6.57 -6.51 -6.46 -6.40 [...]

D:\LAStools\bin>more DGMWA001_323935900.asc

ncols           1000

nrows           1000

xllcorner       393000.00

yllcorner       5900000.00

cellsize        1.00

NODATA_value    -9999.00

-4.73 -4.73 -4.72 -4.72 -4.71 -4.71 -4.71 -4.72 [...]

D:\LAStools\bin>lasgrid.exe -i DGM*.asc -merged -o DGM_merged.asc

D:\LAStools\bin>more DGM_merged.asc

ncols 1350

nrows 2000

xllcorner 392650.000000

yllcorner 5899000.000000

cellsize 1.000000

NODATA_value -9999.0

-9999.0 -9999.0 -9999.0 -9999.0 -9999.0 -9999.0 -9999.0 -9999.0 [...]

D:\LAStools\bin>lasgrid.exe -i DGM*.asc -merged -o DGM_merged_bb.asc -use_bb

D:\LAStools\bin>more DGM_merged_bb.asc

ncols 2000

nrows 2000

xllcorner 392000.000000

yllcorner 5899000.000000

cellsize 1.000000

NODATA_value -9999.0

-9999.0 -9999.0 -9999.0 -9999.0 -9999.0 -9999.0 -9999.0 -9999.0 -9999.0 -9999.0

Regards,

Martin @rapidlasso