Problem Generating DTM LasTools

174 views
Skip to first unread message

Andersson Guerrero

unread,
Jun 20, 2018, 1:15:28 PM6/20/18
to LAStools - efficient tools for LiDAR processing
HI.

Capture laser: LDR0 Velodyne HDL32E.

Normally the workflow consists of correcting the trajectory and generating the cloud.
After that the adjustment of Flight lines is made:


Fig 01. Profile cloud. Only two Flightlines.


the corrections are made in roll, pitch, z, whole data set and per line; in the end, fluctuations are sought and corrected, but its the same result.

An important detail to mention is that the cloud of points seen in the image above has few changes with respect to the cloud without processes, so that would rule out a post-processing error with terrasolid.


After that, we generate DTM with the classification of lastools (because we like terramatch much more than the result), 

lasground -i "d:\\Cloud_adjusted.laz" 
-no_bulge 
-feet 
-ultra_fine 
-odir 

however we note that the result of Blas2dem is a DTM with zones that seem to have noise or strange behavior.

blast2dem -i "d:\\Cloud_adjusted_classified.laz" 
-step 0.3 
-elevation 
-odir 

Fig 02. DTM Lastools.




Tnxs for helpme !!!!!


Jean-François Bourdon

unread,
Jun 20, 2018, 1:51:56 PM6/20/18
to LAStools - efficient tools for LiDAR processing
Hi Andersson,

You probably need to specify blas2dem to only use ground points by adding the parameter -keep_class 2 . I made the mistake not long ago... If I am not mistaken, las2dem and blast2dem use all points available by default to generate a DEM.

Andersson Guerrero

unread,
Jun 20, 2018, 2:26:47 PM6/20/18
to LAStools - efficient tools for LiDAR processing
I forgot written that part in the text, but the DTM have only points class 2, the annotation is important because yes, the raster look dsm but is DTM.

Martin Isenburg

unread,
Jun 21, 2018, 12:58:06 AM6/21/18
to LAStools - efficient command line tools for LIDAR processing
Hello,

You first need to remove noise *below* the ground with lasnoise or lasground will latch the ground surface to those points (if there are many).


But Velodyne LiDAR is also "fluffy" and does not give crisp surfaces so that lasground cannot be used directly. See these workflows for possible ways to create a "median ground" that lies in the middle of the "fluffy" ground surface:


Regards,

Martin @rapidlasso



Reply all
Reply to author
Forward
0 new messages