Getting bare earth from a compiled multipoint

[alexbullen]

Hello, I am working with a very large LIDAR dataset. I have a multipoint feature that was created from all the returns of the LAS files. What I'm wondering is if there is a way to extract the bare earth points from this multipoint that has all the returns in it, or if it is necessary to start from scratch and create a brand new multipoint feature where I only bring in bare earth points from the get-go.

Does anybody have experience extracting bare earth points out of a multipoint feature that was created using all returns?

Thanks, Alex

[alexbullen]

Also, is there a quick and easy way to figure out which of the returns are bare earth, or does this depend on the way the data was gathered?

[XanderBakker]

With what version of ArcGIS are you working? At 10.0 LAS data would be imported as multi point features, but that was incredibly inefficient. As from 10.1 you should be able to create a LAS dataset: ArcGIS Help (10.2, 10.2.1, and 10.2.2)

Using the LAS dataset you can filter for bare earth: ArcGIS Help (10.2, 10.2.1, and 10.2.2)

[XanderBakker]

bare earth are normally those called the "last" return

[alexbullen]

I'm in 10.2. When I pull in the las dataset and use their predefined "Ground" setting, it selects class 2, class 8, and All Returns. I think I'm just going to have to re-do the multipoint with the correct classes selected. However, can I trust these predefined settings? Tests on a small space look accurate enough...

[XanderBakker]

I suppose the info in the classes depend on each provider, but I suppose you should be able to trust it. To generate a DEM you don't have to pass through multi point.

[alexbullen]

The goal is to get a X,Y,Z text file from the points found in the LAS files. THe workflow as I understand it should be LAS ----> multipoint (with proper classifications to pull out only the bare earth points) ----> text file. I've got the text file conversion down, and the LAS are all solid, its just the specifications for the middle multipoint conversion that's in question. Perhaps there's an easier way?

[alexbullen]

I'm just thinking that instead of re-creating the multipoint feature, which will take about 12 hours of processing, it would be great to be able to simply pull points out of the multipoint I already have... like a "Refine Multipoint" tool. Haven't found anything that resembles this so looks like I'll just be starting over. Despite this, I'm still thankful for your responses

Alex