Question about LIDAR and ArcPro

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08-01-2018 04:59 PM
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New Contributor II

Hello there

I recently acquired some Lidar of my municipality and have a few questions about how to go about best using it. The LIDAR is currently classified into bare earth, low, medium and high vegetation.

In the summary sheet that came with the data, it says that the LIDAR is projected to NAD 83 CSRS (2010) UTM ZONE 17N. However, when I bring it into ArcPro (version:2.2.1) and look at the Spatial Reference section in the properties, the .las files are not projected and have an unknown coordinate system.

I was successfully able to use the "Define Projection" Tool to assign NAD 83 CSRS (2010) UTM ZONE 17N to the files, and they rendered in the appropriate spot in my scene. Next I used the "Set LAS Class Codes Using Features" tool with 2d building footprints to separate points into Classification 6 (Buildings). But it didnt quite work as I expected, or rather I didn't notice anything happen. When I change the LAS Filter to Classification 6 (Buildings), nothing renders, I just see the red box. All of the other classifications (bare earth, low, medium, high vegetation) work just fine.

For fun, I used the "Define Projection" Tool again and used the normal NAD 1983 UTM ZONE 17 N projection. Again I used the "Set LAS Class Codes Using Features" Tool with 2d building footprints. This time, IT WORKED! When I changed the LAS Filter to Classification 6 (Buildings) it worked perfectly and I could clearly see the buildings point cloud.

My goal is to use the ArcGIS Solution "Local Government 3D Basemaps" and generate 3d building models from the LIDAR. I ran the test data projected in the normal NAD 1983 UTM ZONE 17 N through the "Local Government 3D Basemaps" tasks and everything looks good. The resulting multi-patch models have correct heights, roof types etc and I feel confident in the results.

Does anyone have advice about this issue? Should I continue with normal NAD 1983 UTM ZONE 17 N projection, even though the LIDAR was collected in NAD 83 CSRS (2010) UTM ZONE 17N? What kinds of issues could I run into?

edit: Location is City of Peterborough, Ontario Canada.

Thank you. I appreciate your time!

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MVP Esteemed Contributor

Andrew, we normally defer such coordinate systems to the expert.

Melita Kennedy‌ … can you provide some commentary on the positional error if the 'wrong' one was used?

(Latitude not specified, but assume southern Ontario... unless corrected by Andrew.)

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Esri Notable Contributor

NAD 1983 CSRS is the "readjustment" of the original NAD 1983 in Canada. A lot of people use "NAD 1983" when they have data that really in CSRS (or a later realization in the USA). 

If you really had original NAD 1983 data, offsets between it and CSRS should still be sub-meter in southern Ontario. Unfortunately, Esri software doesn't have any data for NAD 1983 - CSRS transformations in Canada. They were released by the individual provinces and sometimes we need to arrange permissions to redistribute the files. 

I poked around on NRCan websites but didn't find a converter or a way to check historical coordinates on a control network point.

When you defined the data with NAD 1983 CSRS (2010) UTM 17N, did you make a custom coordinate system definition? If you did, you might try to use the just NAD 1983 CSRS-based definition, 2958 (you can type that into the search box). I'm trying to determine if there's an issue with using a custom GCS, something more general!

Melita