topic Re: What is the proper work flow to extract ground points only from .LAZ in ReCap Forum

What is the proper work flow to extract ground points only from .LAZ

Sylvino — Thu, 13 Feb 2025 17:50:45 GMT

Hi all, I'd like to ensure that I am using the proper workflow to extract ground points only using Recap Pro 2025.

Step 1: Create project, set coordinate system, and import data (decimated to 100mm) Also is it possible to add coordinate systems to Recap?

Step 2: Index scans then launch project

Step 3: My data already has classification so in the classification options I delete everything except for OG and low vegetation by selecting the "X" beside each classification. I find this helps speed up the next step.

Step 4: Optimize the project since I deleted points

Step 5: Automatic ground classification using optimum

Step 6: Save and optimize

Did I do this correctly? Since the laz file is already classified, could I have skipped step 5?

Also, how do I see how many points my project has?

Link to las file:

https://www.dropbox.com/scl/fi/fhxhacsochavgnd976kys/LiDAR-clipped.laz?rlkey=ewnebugfedw20u97l4lko33m6&st=0koxiqxg&dl=0

Re: What is the proper work flow to extract ground points only from .LAZ

Pointdump — Thu, 13 Feb 2025 18:18:48 GMT

Sylvain,
Thanks for posting link to your data. I'm loading it right now.
"Also is it possible to add coordinate systems to Recap?"
Yes. You can create a custom coordinate system definition in Civil3D/Map3D's MAPCSLIBRARY and ReCap will read from that.
"Since the laz file is already classified, could I have skipped step 5?"
No, because step 3 still has "low vegetation". After you use automatic ground classification you need to delete everything but the Ground(2) classification before exporting.
Dave

Re: What is the proper work flow to extract ground points only from .LAZ

Pointdump — Thu, 13 Feb 2025 18:41:36 GMT

Sylvain,
Reading the header, lasinfo in lastools shows your point cloud is in >>>EPSG:2958<<<, NAD83(CSRS)/UTM zone 17N.
Dave

Edit: More info

WKT OGC COORDINATE SYSTEM:
COMPD_CS["NAD83(CSRS) / UTM zone 17N + CGVD2013 height",PROJCS["NAD83(CSRS) / UTM zone 17N",GEOGCS["NAD83(CSRS)",DATUM["NAD83_Canadian_Spatial_Reference_System",SPHEROID["GRS 1980",6378137,298.257222101,AUTHORITY["EPSG","7019"]],AUTHORITY["EPSG","6140"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4617"]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",0],PARAMETER["central_meridian",-81],PARAMETER["scale_factor",0.9996],PARAMETER["false_easting",500000],PARAMETER["false_northing",0],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AXIS["Easting",EAST],AXIS["Northing",NORTH],AUTHORITY["EPSG","2958"]],VERT_CS["CGVD2013(CGG2013) height",VERT_DATUM["Canadian Geodetic Vertical Datum of 2013 (CGG2013)",2005,AUTHORITY["EPSG","1127"]],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AXIS["Gravity-related height",UP],AUTHORITY["EPSG","6647"]],AUTHORITY["EPSG","6660"]]

histogram of classification of points:
4236041 ground (2)
5606353 low vegetation (3)
5174022 medium vegetation (4)
42568209 high vegetation (5)
53233 noise (7)
1472 Reserved for ASPRS Definition (18)