[Qgis-user] las files

[Garth Fletcher]

Andreas Neumann recommended:
> If you want to go the "free" route you'll have to use PDAL outside of 
> QGIS (on the command-line) and convert them to GeoTIFF files. Have a 
> look at the PLAS tutorials at https://pdal.io/tutorial/index.html

I concur with using PDAL - it worked very well for me for converting
50+ Lidar tiles (~ 5 GB) into a GeoTiff DEM which works with QGIS.


Under Mac OS X 10.12 (Sierra) I used PDAL in the Terminal window. i.e.,
using "command lines".

Here are my somewhat cryptic notes about the process:

--------------------------------------------
first merged all the .las into all.las extracting the type 2 (ground) 
and 9 (water)
--------------------------------------------
CD folder containing the .las files to be merged
pdal pipeline P2.json

  where file P2.json contained:
{
"pipeline":[
{
"filename":"19*.las"
},
{
"type":"filters.range",
"limits":"Classification[2:2], Classification[9:9]"
},
{
"type":"writers.las",
"filename":"all_plus.las"
}
]
}
resulted in 680 MB all_plus.las file


--------------------------------------------
then converted to GeoTIFF with 6' x 6' cells
--------------------------------------------
pdal pipeline Ptiff.json

  where file Ptiff.json contained:
{
"pipeline":[
{
"filename":"all_plus.las"
},
{
"type":"filters.reprojection",
"out_srs":"EPSG:3614"
},
{
"type":"filters.range",
"limits":"Classification[2:2], Classification[9:9]"
},
{
"type":"writers.gdal",
"filename":"all_plus.tif",
"output_type":"min",
"resolution": 6.0,
"radius": 9.0,
"window_size":1,
"data_type":"float"
}
]
}
created 198 MB file all_plus.tif

--------------------------------------------
Notes:
--------------------------------------------
I extracted Class 2 (ground) and Class 9 (water) to get "surface" points

In our area the tif contained a number of "noData" pixels where no
  points were found within a pixel (6' x 6' area for our case) which
  were classified as Ground or Water.  Using larger cells, e.g., 12x12,
  reduces the number of noData cells, but does not eliminated them.

QGIS > Processing > GDAL > Raster Analysis > Fill nodata
  was then used to fill in the remaining noData cells through
  interpolation from adjacent areas.  I used a maximum reach of 30.

I wanted to create contours.  When the raw Tif DEM was used the contours
  were very "busy", i.e., full of little jaggedy wiggles.

So the next step was to use
   QGIS > Processing > SAGA > Raster filter > Gaussian filter
  to "smooth" the DEM.  Settings of 2 for SD and 5 for Radius seemed to
  produce acceptable contour smoothness for 5' contours

Final step was to use
   QGIS > Processing > GDAL > Raster Extraction > contour
  to create the contour layer.

I hope the above helps guide you through the process
-- 
Garth Fletcher