I know this is nothing new, but it's new to me. I'm familiar with generating contours from TIN's or points, but not with LAS files. I've downloaded a LAS file from available state data. What is the best software to convert to ascii or way to generate contours? I'm currently running Carlson Survey. Will I need to purchase Carlson Point Cloud or is there another option I'm unaware of? Curious how everyone else using Carlson Survey is going about this.
LAS basically is point cloud data. So I would not be surprised if you did need a special module to handle it.
Is the elevation data available in another format? LAS is pretty raw, and you may find there are clean DTM and DEM datasets available in something like GeoTIFF
Check out BricsCAD, creating surfaces from point clouds is super easy. The Pro version is likely what you would need. They have a 30 day trial period.
I usually use Leica Infinity to work with point cloud data. Sometimes what I will do is thin out the point cloud there and then export a PTS file of the thinned out cloud and in Excel add/remove columns as needed to get it into CAD as a PENZ coordinate file, and then standard TIN creation in CAD is the next step. I like this method of combining LiDAR data and conventional survey data to put together deliverables.
If you're working with a cleaned and QC'd LAS from a state website, you might be able to get away with just generating a surface. But even those, in my experience, are often too dense for typical CAD software, and unless you sample the LAS file you'll both bog down the drawing file and end up with really goofy-looking contours.
I too would be looking for a DEM in TIF format. Some states already have contours as shapefiles to be downloaded...
<div>LAS/LAZ is a very useful and important format. Keep in mind that the point contents are usually classified meaning you want to extract only the ground points (class 2). To do this, take a look at the LASTOOLS freeware ....</div><div>
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... by the late great Martin Isenburg.
https://lidarmag.com/2021/10/30/in-memoriam-martin-isenburg-1972-2021/
It should let you extract the ground points to a .TXT file and possibly thin the contents. There are usually many more points than you need to create a surface. Trying to create a TinSurface from all the ground points in a large area can bog down most machines depending on its hardware.
Creating a GridSurface (DEM/Raster) as specified cell sizes can minimize the data burden, but you may lose details you wanted to keep (such as ditches, etc).
Carlson Point Cloud is good but expensive. Their topo Precision 3d is a lot less expensive than PC and can get you started. 30 day free trials too.
Since Version 3.32 (June 2023??) QGIS (an open-source and free GIS program) has had native LiDAR tools that seem to be working well.
The basic workflow will be to bring the LAS/LAZ file into QGIS, then "Export to raster" to create a TIF file to work with in Carlson.
In Carlson, go to "Grid File Utilities", then "Import Grid", and select "Import DEM" and select the TIF file to create a Carlson GRD file. Finally, use "Contour from Grid File" to create contours.
Refining the basic workflow will add filtering the LiDAR data to get the desired information, such as only ground elevations. Depending on the circumstances, it may be desirable to densify the raster file created in QGIS.
Also, when I went through the preceding process today using a LAZ file from USGS the LiDAR coordinate system was UTM on NAD83(2011) and my Carlson 2021 does seem to allow UTM on anything other than WGS84 so it was necessary to reproject the TIF file in QGIS. Will need to update to Carlson 2024 and see if that limitation still exists.
If this helps, make sure to kick a few bucks to the QGIS Foundation to keep that great resource going!
GB
I have the option to download a whole counties contour DWG file but it’s very slow to work with due to size. I wish I could select a project area and download a shp file, but can’t seem to find that option anywhere. Thanks for the responses, I really appreciate the advice.
I have the option to download a whole counties contour DWG file but it’s very slow to work with due to size. I wish I could select a project area and download a shp file, but can’t seem to find that option anywhere.
Glenn mentioned QGIS - this could solve the bogging-down problem. Download CAD contours, bring into QGIS (set that coordinate system correctly!), clip them to project area, export out again (SHP or DWG) then bring into your CAD software.
Between LAS, DEM, and contour files, I'll take the DEM 95% of the time. LAS are a pain to work with in CAD software (especially for generating surfaces), and TIN surfaces do some funky things when drawn off of contours.
It's far easier to create a surface from a DEM, and if I want to I can resample it in GIS before I do so...
