Lidar rooftop analysis

[Steve Liddle]

Hi again

Just tring to get my head round this error:

***********************************
* Welcome to LidarRooftopAnalysis *
* Powered by WhiteboxTools        *
* www.whiteboxgeo.com             *
***********************************
Reading data...
Clipping lidar to building footprints...
Clipping: TEST
Building roof facet models...
Segmenting the point cloud...
Saving polygon data...
thread 'main' panicked at 'The file does not currently contain any record data.', whitebox-tools-app\src\main.rs:72:21
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

I have a *.las file that only has unclassified, ground or road surfaces type points. Does this mean the rooftop analysis won't work even if I have a corresponding shape file the building outlines? I can import the two files to Progecad (Autocad clone) and they line up nicely.

[Whitebox Geospatial Inc]

Hi Steve,

 

I’d check to make sure that your building footprint vector in the same projection as your input lidar point cloud file.

 

Regards,

 

John

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[Steve Liddle]

Here's a couple of screenshots from my cad program. The files seem to line up ok. Could it be that the difference in height between the building shape file and the absolute values in the point cloud are too far apart? You can see the difference in the second screenshot. Probably 10 metres or so.

[Whitebox Geospatial Inc]

Hi Steve,

 

Just because they line up okay in the CAD program, doesn’t mean that they share the same projection. You can see the projection of the Lidar data by using the LidarInfo tool and looking at the variable length records (VLR). The projection of the polygon shapefile can be determined by opening it up in a GIS like QGIS and looking at the layer properties. They must be the same, otherwise you will get an error indicating that the file contains no record data.

 

Regards,

 

John

 

From: whiteb...@googlegroups.com <whiteb...@googlegroups.com> on behalf of Steve Liddle <springwe...@gmail.com>
Date: Wednesday, May 10, 2023 at 3:51 PM
To: WhiteboxTools <whiteb...@googlegroups.com>
Subject: Re: Lidar rooftop analysis

Here's a couple of screenshots from my cad program. The files seem to line up ok. Could it be that the difference in height between the building shape file and the absolute values in the point cloud are too far apart? You can see the difference in the second screenshot. Probably 10 metres or so.

 

To view this discussion on the web visit https://groups.google.com/d/msgid/whiteboxtools/81883254-33b6-464e-a9d4-995a5b2e2f88n%40googlegroups.com.

[Steve Liddle]

Ok, thanks very much for the tip, John! I'll dig into it during the next few days.

[Steve Liddle]

A quick check of the lidar info file (test.las) I generated yesterday shows the following:

Variable Length Records

VLRs have not been set.

So seems to explain it :-)

The *.prj file which is associated with the .shp file with the buildings has a bunch of info 

PROJCS["SWEREF99_TM",GEOGCS["GCS_SWEREF99",DATUM["D_SWEREF99",SPHEROID["GRS_1980",6378137.0,298.257222101]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Transverse_Mercator"],....etc. etc.

Shame that the company I buy this type of data from neglect to provide this information in the LAS file. I'll start a support ticket with them.

Thanks for your swift responses, John. Much appreciated.