topic Re: LAS ESRI vs LAS USGS in LIDAR Resources Questions

LAS ESRI vs LAS USGS

JerryMahun — Tue, 04 Aug 2020 16:59:26 GMT

What is the difference between LAS ESRI and LAS USGS formats? I see both types available for a number of Wisconsin county LiDAR data sets.

Re: LAS ESRI vs LAS USGS

CodyBenkelman — Fri, 21 Aug 2020 19:09:42 GMT

Jerry

Sorry for the delay - I did not see your post. There should not be anything labeled "LAS ESRI" format so I'd ask the source (State of Wisconsin?) to clarify and likely change what they have written... There is no LAS ESRI format unless they're referring to compressed data; we do have an open format referred to as zLAS for data compression. If that's what they're hosting for download, their documentation should be more clear. Could you post a link to where you found this?

If this does refer to zLAS format and you need advice on that, let us know. Briefly, zLAS is compressed roughly 6:1 and can be read/used directly in ArcGIS w/o decompression.

Thanks

Cody B.

Re: LAS ESRI vs LAS USGS

JerryMahun — Fri, 21 Aug 2020 19:58:16 GMT

Well, there is. See https://bin.ssec.wisc.edu/pub/wisconsinview/lidar/Taylor/Taylor_2016_3DEP_Delivery/.

Using AutoDesk ReCap, I opened both versions of the same file (they're the same size) and they looked identical.

I don't know how many other counties have both ESRI and USGS las files. Will try to track down more information.

Jerry M

Re: LAS ESRI vs LAS USGS

CodyBenkelman — Mon, 24 Aug 2020 15:37:57 GMT

I did a binary comparison, and those files are the same, with the exception of some metadata tags.

As for why they are there, I can't say. I looked at several other counties on the Wisconsin server, and none of the others showed "Classified_LAS_esri" . There appears to be quite a bit of variation in what is available from one county to the next - you'd have to ask them why this one county has different files for Esri vs. USGS.

Note ArcGIS can perform point classification, so perhaps this was a test they ran to compare classification results using ArcGIS vs. the classification provided by USGS.

Cody B

Re: LAS ESRI vs LAS USGS

JerryMahun — Mon, 24 Aug 2020 18:08:35 GMT

I sent an email to the WisconsinView manager and this was his response:

Jerry, the reason we have two sets in some counties is that a strict definition of Wisconsin County Coordinate System (WISCRS) parameters by USGS in the LAS header does not show up or visualize correctly in a map space used in ESRI products like ArcMAP. Its shows up shifted several miles to the SE in relation to other base map features. The folder labeled LAS_ESRI has the WISCRS projection parameters used by ESRI loaded in the LAS header. So if you are planning to use the LAS files in ESRI products I would recommend downloading the LAS_ESRI tiles. The USGS funded acquisition of many of the more recent counties in Wisconsin, so we offer those too.

If you end up with Wisconsin LAS tiles that appear to be shifted relative to other features in ESRI products, one can easily fix the shift by use of a .PRJ with the ESRI parameters for that Wisconsin county (hint: use the PRJ from the tile index shapefile and create .PRJs for all the LAS tiles - there's a script for that in the Arctoolbox). Likewise, in a LASD mosaic you can go to the horizontal coordinate system tab and fix the whole mosaic without changing the individual LAS tiles.

Its not clear to us who is right and who is wrong, or why the shift occurs at all. But with two big organizations who both know more than I do, its hard to get this fixed. In later collections, we offer only the USGS LAS tiles, but include a folder with the .PRJs too. Sorry for the confusion. I blame human stubbornness.

let me know if you need further assistance.

Jim Giglierano

WDOA

Re: LAS ESRI vs LAS USGS

CodyBenkelman — Mon, 24 Aug 2020 20:21:54 GMT

Jerry

thanks for following up on this. I had not heard about this issue with the Wisconsin County Coordinate System (WISCRS) parameters but now we know why there are 2 versions of files in some cases. (I'm glad they switched to offering *.prj files as the workaround - that's a very LOW data volume solution vs. creating separate LAS file copies).

I've tested in ArcGIS Pro 2.6 and ArcMap 10.7.1, and the Wisconsin County Coordinate System (WISCRS) formatted data works properly. Whatever caused the problem in the past has presumably been fixed, but users on older versions of the software may still need this workaround. If you or anyone reading this needs further details please let me know.

Cody B.

Re: LAS ESRI vs LAS USGS

JerryMahun — Mon, 24 Aug 2020 20:57:48 GMT

Thanks for letting me know. I'll pass the information on to WisconsinView manager.

Jerry