LiDAR generated surfaces

[Anonymous]

I have recently upgraded to Civil 3D 2011 when we started receiving LiDAR data.  I have been playing around with the data a bit and have a few questions on how the data is dealt with.  It appears that when a point cloud is added to a surface, it is using the point cloud display somehow to generate the TIN.  I believe that the point cloud display is showing a percentage of points based on the maximum number of 1.5 million points.  On these particular datasets (citywide LiDAR coverage, about 2,600' x 2,600' panels), we may have 4-7 million points in each LAS file.  Is Civil 3D ignoring all points beyond 1.5 million in surface building operations?  Also, when adjusting the slider, is there any way to know which points will be displayed...or maybe the points are reduced randomly??

Thanks!

[thesieb]

I would like to know the same thing... Creating a surface from a point cloud (created from an ESRI grid or ESRI ascii file) seems to use only a fraction of the points available... and I don't see anywhere to choose to weed point in the surface creation.

Also, it creates a TIN surface... is there any way (or benefit) to create a GRID surface from teh point cloud?

John

[BrianHailey]

The points the point cloud displays are the ones that are added to the surface. If you want the maximum number of points to be added to your surface, slide the slider all the way to 100.

Also, if you filter the points based on the classification, only the points that displayed will be added. According to the help file, the max number of points that a point cloud object will display is 750,000 points. If you need all the points in your surface, you'll have to bypass the point clould option and simply add the point file directly to a surface.

[Anonymous]

You may want to check out some of the Feature Extraction and Shape Extraction tools being developed by Autodesk labs..

http://labs.blogs.com/its_alive_in_the_lab/

they posted some download links back on 2/18/2011

I haven't tried them yet, but it is obvious Autodesk is working on improving their point cloud tools, plus it gives you a chance to add your 2 cents and provide input on what they develop...

I'm working with a point cloud that has 900 million points, so I'm still doing most of the work with another software, but I hope Autodesk develops the ability to render point clouds sometime soon!  They are almost there!

Mark.

[Anonymous]

After opening my point cloud, I tried to isolate a group of points (i.e. Ground, low veg, high veg..) but I can't seem to be able too.  I go to the point cloud properties, then classification tab to turn on a layer by checking it and changing it to another color (btw...all of my points are grey already.  There is no distinction between different classified points.)  All of the points are a grey "ByLayer" color and when I try to isolate 'ground points', everything stays grey; nothing happens.

Let me know your thoughts.

[Neilw_05]

I posted about this same question here: http://forums.autodesk.com/t5/AutoCAD-Civil-3D/Clip-or-filter-point-cloud/m-p/3144490/highlight/true...

I decided the point clould tool was too problematic for building the surfaces and instead used the XYZ file and a data clip boundary which gave 100% fidelity.

The density setting is still useful for viewing the clouds.

[mathewkol]

Mark, those tools were removed Feb 1 I believe.

I'm with Neil, I see little need for a point cloud in C3D at this point in the game. It's just an extra step getting a surface...and with the limited number of points, it just doesn't seem worth it.

[BrianHailey]

I think it was the point cloud feature extraction tools that expired, not the point clouds themself. There are still point clouds in Civil 3D.

As for the use of point clouds, I've been disapointed as well. The first release, all we could do was look at the point cloud. The next release we could add points to a surface (but not necessarily all of them). Perhaps in a future release we'll be able to display point clouds in a profile or cross section and target a point cloud for a corridor. That would make it useful.

[mathewkol]

Indeed, Brian, it was the Labs tools.

[thepworth]

My biggest gripe about howC3D handles point clouds is when you move the slider, it's arbitrary.  What I'd love to see is a means to build a surface by 1) set contour interval 2) initial estimate 3) weed points 4) check against Nat'l map accuracy stds i.e. 90% of all points w/in 1/2 contour interval, 5) weed until accuracy threshold is met.

would make a lot more sense than "visually estimate that contours don't appear too degraded, which is kinda where they're at now 😞

[Neilw_05]

Rather than compare with an unrelated source such as the national map, I think it would be best if we could compare the decimated set vs. the unaltered set, perhaps by comparing contours.

I also would like to see more control over what gets removed than just a density slider. Ultimately it would probably lead to a set of full fledged editing tools.

[thepworth]

Concur - I'm referring to the standards & ASPRS standards and "internal" data consistency versus saying we need to be within USGS topo contours.  I just wasn't too verbose - still getting used to time change 😉

If I were back in school, this would be a worthy topic for how to most efficiently weed a lidar data set.

I do know that LizardTech (Mr. Sid) has gone in with my old employer (Merrick) to see how they might apply the pyramid scheme of SID's to LiDAR data sets.  what Merrick has done with their MARS software is orders of magnitude faster at processing than AD.  

[Anonymous]

I am adding points for a LIDAR point cloud to a surface .  I've seen in tutorials and other forums that one should be able to change your surface style to "Contours .5' and 2.5' with Points" and when I go to do it on mine, I cannot find that style on my dropdown menu.  What I am doing wrong??

[thepworth]

the style needs to exist in your drawing - you can copy an existing one (1' & 5') and change the contour interval as you want.  .5 & 2.5 is not a typical interval.

[Anonymous]

This is sort of related to LiDAR and Point Clouds, but more of a surface question.  What have you all done to smooth out a surface with all the points one gets with a LiDAR dataset?  When I make a surface directly, it almost always results in pretty jagged and erractic contours.

One thing I have done is created a surface and exported it as a DEM.  I played with cell size a bit and always told it to average points rather than take the center.  It seemed to result in a representative surface when it worked, but it hasn't always worked the way I thought it would and it's pretty time consuming.

Thanks!

[Neilw_05]

Usually when we get LIDAR data it comes with points in text file along with a CAD file with 3D breaklines which need to be added to the surface. Without the breaklines the surface would be inaccurate and jaggy. So far I haven't had to do any smoothing on the models we've built.