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.