My LIDAR files are .asc files

[Dr. Ian Smith]

I'm a complete newbie.

All my LIDAR files are .asc files. Do I need to convert to .las files before I can use lastools?

[Terje Mathisen]

No (LAStools binaries support asc), but you should!

If you start by converting to LAZ (not just LAS) you will save at least
95% (maybe even more?) of your disk space and all subsequent processing
will be much more efficient.

Terje

--
- <Terje.M...@tmsw.no>
"almost all programming can be viewed as an exercise in caching"

[Martin Isenburg]

Hello,

if your files have the *.asc file extension then they are usually gridded rasters which you can verify by looking at the first few lines that should look something like this:

C:\software\LAStools\bin>more zurich_dsm20cm.asc

ncols 500

nrows 500

xllcorner 676750.000000

yllcorner 246000.000000

cellsize 0.200000

NODATA_value -9999.0

553.85 554.05 554.51 554.84 554.13 554.04 553.21 553.41 552.41 [...]

This means you do not have the raw LiDAR points potentially a raster product such a DSM, a DTM, or a CHM that was derived from LiDAR. To process such files with LAStools you could then follow more or less (depending on the resolution of the raster) the kind of workflows that we have for getting reasonable DTMs from dense-matching photogrammetry. Check these articles on our company blog that often provide the data and guide you through step by step:

https://rapidlasso.com/2017/07/04/removing-excessive-low-noise-from-dense-matching-point-clouds/

https://rapidlasso.com/2017/06/13/integrating-external-ground-points-in-forests-to-improve-dtm-from-dense-matching-photogrammetry/

https://rapidlasso.com/2016/11/22/creating-a-better-dtm-from-photogrammetic-points-by-avoiding-shadows/

https://rapidlasso.com/2015/10/07/removing-low-noise-from-semi-global-matching-points/

https://rapidlasso.com/2015/09/21/creating-dtms-from-dense-matched-points-of-uav-imagery-from-senseflys-ebee/

https://rapidlasso.com/2014/08/25/processing-large-dense-matching-point-clouds/

https://rapidlasso.com/2014/06/13/dtm-from-dense-matching-points/

And as Terje suggests you may want to convert the ASC points to LAZ with lasoptimize so you also have a space-filling order instead of a line by line order for the points in the file.

Regards,

Martin @rapidlasso

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[Dr. Ian Smith]

Thanks Martin,

You are correct - I have .asc files that start as you say. So I have raster DSM files. I have followed up on your links.

I have the feeling that the LIDAR images I have are of a very poor quality? Is it even worth attempting to clean them up?

This is the best I have of a clump of trees. I am attempting to look at the terrain underneath.

Will I be wasting my time?

Regards

Ian

[J. Thaddeus Eldredge]

Try changing your color ramps to make the elevations pop.  It is hard to see what you have there.

J. Thaddeus Eldredge, PLS, CFM

East-SouthEast, LLC

1038 Main Street

Chatham, MA 02633

508-945-3965

www.ESE-LLC.com

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