LIDAR Point Density Reduction and Import Best Practices

[sethdwelter795266]

Hi,

I am curious how to import LIDAR into Civil 3D. I haven't done the process yet and would like to know any helpful advice!

Searching this forum I found this:

"Summary: The ability to use DEM files in the current SDTS format, or in ESRI's grid format, to define the grid surface.
And the ability to set the precision prior to import

"Description: I would like to see grid surfaces reworked.

"The grid surface is the red-headed stepchild of C3D - all the development work is going into improved TIN performance. Meanwhile, technology seems to be heading the other way - I'm seeing more and more data (LIDAR, multi-beam bathymetry, etc.) provided in grid form. Many of these datasets are also too large for a C3D TIN surface to handle. By definition, a grid needs about 1/3 the memory footprint of a TIN created with the same data points.

"And we can't use that data without a lot of translation steps, because the only definition option for grid surfaces is to import a DEM file formatted to the *old* USGS standard. So here's really the first part of my wish - the ability to use DEM files in the current SDTS format, or in ESRI's grid format, to define the grid surface.

"It should also be possible to increase grid surface performance & reduce memory footprint by reducing the elevation values from double precision to single. There is no elevation on the surface of the earth that needs 16-place accuracy. Grids can represent concepts other than topography, too - in some cases, the values could even be integer.

"How Used: I have a LIDAR surface in ESRI's grid format that covers 120 square kilometers with a 1-meter point density. That's right, 120 million points.

"If I need a portion of that surface in C3D, I currently start in ArcView, and export the grid to a point shapefile, clip the point shapefile to just the bare minimum area I need, add X & Y data columns, and export the shapefile to a .csv point file. Then I fire up C3D and create a TIN, using the .csv point file as part of the surface definition. Great, I've got a surface - unless there's more than about a million points in the .csv, in which case C3D will crash.

"What I should be able to do is create a grid surface and select the ESRI grid file as a definition item, apply a boundary, and be ready to roll with profiles, grading, corridors - the works.

"Feature Affinity: Surface Modeling

Submitted By: Earl Kubaskie on August 23, 2007"

That's the end of that quote! Sorry if you read it all. But I noticed that it was posted 2007. I'm guessing the process changed since then. Is this process he lays out more or less correct? Or is there a better way to import lidar data.

Thanks,
Seth

[Opie]

What format is your data currently in? Surfaces can be created a couple of ways using DEM files. If the coordinates of the drawing match the DEM file, you could create a surface directly from the DEM.

If the drawing coordinates do not match the DEM file, then you would create a TIN surface and then add your DEM file to that, making sure to specify the coordinates of the DEM file upon insertion. This will allow C3D to transform the DEM to the drawing's coordinates.

[dotson]

Civil3D: Lidar Straight To TinSurface
http://dotsoft.com/blog/?p=508

[BlackBox]

Dotson offered an awesome tool... Which I am off to tinker with, as I didn't realize it was free until just now. Ehhehehe

---

The only other way I know to import a reduced area from DEM as Surface in Civil 3D, is to open a single, large, County-wide DEM using QGIS (which is also free), I'll usually import a project boundary or larger rectangle around it (via MAPEXPORT from C3D) for the area I need, zoom to that in QGIS and export that area of the DEM to my project as a new (much smaller) DEM, then add that to C3D as Surface.

Cheers

[sethdwelter795266]

Ok, I will try that. Thank you