Lidar DTM to Point cloud

[Brian Tovey]

Is it possible to convert a lidar dtm back to the point cloud using either QGIS of Lastools

Brian Tovey

[Terje Mathisen]

'Brian Tovey' via LAStools - efficient tools for LiDAR processing wrote:
> Is it possible to convert a lidar dtm back to the point cloud using
> either QGIS of Lastools

Yes and no:

No, you cannot retreive any individual points that was discarded during
the construction of the terrain model.

Yes, you can convert each cell in the DTM back to a single virtual point
located in the center of it. This is then just a way to store the DTM,
it does not add or remove any info.

Terje
>
> Brian Tovey
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- <Terje.M...@tmsw.no>
"almost all programming can be viewed as an exercise in caching"

[Martin Isenburg]

Hello,

a raster really is a point cloud whose x/y coordinates lie on a perfect grid. Obviously you will never get the original LiDAR (or photogrammetry) points back back if you want the DTM to be represented by a point cloud format instead of by a raster format then you can do the following if you have a DTM in BIL, ASC, DTM (from "FUSION") or XYZ format:

las2las -i dtm.bil -o dtm.laz

las2las -i dtm.asc -o dtm.laz

las2las -i dtm.dtm -o dtm.laz  

las2las -i dtm.xyz -o dtm.laz

If you have the DTM in any other format such as TIF or IMG then you'll first have to use GDAL / QGIS to convert it to the BIL format and then use the command shown above. I've been repeatedly told that the LAZ format is one of the most compressed *raster* formats there are. Here a little demonstration of how much smaller a raster in LAZ format can be compared to TIF, IMG, BIL and ASC formats. In this example it's only 36% the size of the next smallest raster, the TIF format.

las2dem -i ..\data\zurich.laz -step 0.2 -spike_free 0.6 -o zurich.tif

las2dem -i ..\data\zurich.laz -step 0.2 -spike_free 0.6 -o zurich.img

las2dem -i ..\data\zurich.laz -step 0.2 -spike_free 0.6 -o zurich.bil

las2dem -i ..\data\zurich.laz -step 0.2 -spike_free 0.6 -o zurich.asc

las2dem -i ..\data\zurich.laz -step 0.2 -spike_free 0.6 -o zurich.laz

e:\LAStools\bin>dir zurich*

04/09/2018  02:03 PM         1,750,616 zurich.asc

04/09/2018  02:02 PM         1,000,000 zurich.bil

04/09/2018  02:02 PM                77 zurich.blw

04/09/2018  02:02 PM               225 zurich.hdr

04/09/2018  02:02 PM         1,034,824 zurich.img

04/09/2018  02:03 PM           189,730 zurich.laz

04/09/2018  02:02 PM                77 zurich.tfw

04/09/2018  02:02 PM           524,142 zurich.tif

Regards,

Martin @rapidlasso

On Mon, Apr 9, 2018 at 12:36 PM, 'Brian Tovey' via LAStools - efficient tools for LiDAR processing <last...@googlegroups.com> wrote:

Is it possible to convert a lidar dtm back to the point cloud using either QGIS of Lastools

Brian Tovey

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