I've been struggling with this for the past few days. I want to create a DEM of a flood control area, which is covered in low/intermediate-height vegetation (pioneers and reed mostly). The point cloud data with x, y and z comes from airborne LiDAR and I've been able to load it into QGIS by conversion and translation and managed to create a DSM.
From false-colored images, I know the locations where the vegetation is present. Is there a way to get an actual DEM of the area by removing the low/intermediate-vegetation? My aim is to obtain a DEM to analyze the flooding area, so an increase in the accuracy of the elevation data would be very useful.
Part of the headerless .txt file LIDAR; so x coord, y coord and z coord / elevation;
147675.500 210500.500 10.15
etc Ln 1805277, Col 1 (Notepad)
This is how the DTM looks after I've loaded the text file via Raster>Conversion>Translation and used a IDW-interpolation:
This is de CIR image from the area, showing the vegetation cover:
I thought when using LASTools I could extract the bare ground, so first I've used txt2las to convert the .txt file to a .las file. When running the lasinfo on this newly created .las file, this is what I get:
reporting all LAS header entries:
file signature: 'LASF'
file source ID: 0
global_encoding: 0
project ID GUID data 1-4: 00000000-0000-0000-0000-000000000000
version major.minor: 1.2
system identifier: 'LAStools (c) by rapidlasso GmbH'
generating software: 'txt2las (version 200101)'
file creation day/year: 70/2021
header size: 227
offset to point data: 321
number var. length records: 1
point data format: 0
point data record length: 20
number of point records: 1805276
number of points by return: 1805276 0 0 0 0
scale factor x y z: 10 10 10
offset x y z: 0 0 0
min x y z: 147680 210500 -10
max x y z: 150000 213000 20
variable length header record 1 of 1:
reserved 0
user ID 'LASF_Projection'
record ID 34735
length after header 40
description 'by LAStools of rapidlasso GmbH'
GeoKeyDirectoryTag version 1.1.0 number of keys 4
key 1024 tiff_tag_location 0 count 1 value_offset 1 - GTModelTypeGeoKey: ModelTypeProjected
key 3072 tiff_tag_location 0 count 1 value_offset 31370 - ProjectedCSTypeGeoKey: Belge 1972 / Belgian Lambert 72
key 3076 tiff_tag_location 0 count 1 value_offset 9001 - ProjLinearUnitsGeoKey: Linear_Meter
key 4099 tiff_tag_location 0 count 1 value_offset 9001 - VerticalUnitsGeoKey: Linear_Meter
reporting minimum and maximum for all LAS point record entries ...
X 14768 15000
Y 21050 21300
Z -1 2
intensity 0 0
return_number 1 1
number_of_returns 1 1
edge_of_flight_line 0 0
scan_direction_flag 0 0
classification 0 0
scan_angle_rank 0 0
user_data 0 0
point_source_ID 0 0
number of first returns: 1805276
number of intermediate returns: 0
number of last returns: 1805276
number of single returns: 1805276
overview over number of returns of given pulse: 1805276 0 0 0 0 0 0
histogram of classification of points:
1805276 never classified (0)
So none of the points is classified as anything.
I use QGIS 3.16 and the LiDAR data I received is in headerless .txt format. I've tried LAStools and converted the LiDAR .txt into .las, but the las2dem is not giving an output file and says:
WARNING: unlicensed. over 1.5 million points. inserting black diagonal.
ERROR: cannot find triangle in first 10000 points.
As you can probably tell, I'm very much a beginner in QGIS.
