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Discussion: LiDAR Question

in: Orienteering; General

Mar 9, 2021 10:57 PM # 
ajriley:
Hi, I have an LAZ file I downloaded near me in CA that seems to say there is "no projection" for the data and I'm just kind of confused because now I'm not sure if the data is in meters or feet or if its just corrupted data?

Anyone have experience with how to fix this, should I just run it through Karta as is and it just won't be properly georeferenced?
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Mar 9, 2021 11:21 PM # 
gordhun:
It would help me to answer if I knew where you got the LiDAR data and where you are trying to load it.
If the LiDAR is from the National Map Viewer they are incredibly careless in their metadata in identifying whether the tile is in the UTM, State Plane or some other projection. By default they seem to say Transverse Mercator but often it turns out to be State Plane.
One way to find out is by trial and error.
Another is to look through the metadata and if either the planar or the vertical data is said to be in feet then the projection is NOT UTM.
I'm guessing you are not using OCAD. But if you were and could not get the LiDAR loaded in the right place an easy way to get started is to just open a new OCAD file and slap the LiDAR tile in there first thing. The only thing you will have to do is correctly identify the UTM zone for the area. OCAD will do the rest in geo-referencing the map.
Mar 10, 2021 2:28 AM # 
haywoodkb:
Seems I remember California having some unusual LIDAR data formats. "no projection" means it is still in geographic coordinates: degrees of latlong. You will need to convert to UTM projection for use with Pullautin. It is probably using feet instead meters. You could try it both ways and see if it produces realistic results.
Mar 10, 2021 6:49 PM # 
ajriley:
This is for Stanford Dish / Arastradero near Stanford, I just wanted to make sure I remembered how to make a Karta map (clearly not).

I doubt the data is in UTM, but how would I go about changing it to UTM?

@haywoodkb If it says no projection do I just need the right UTM Zone? Like -utm 18north? And then change the elevation? Not really sure the process here.
Mar 10, 2021 7:26 PM # 
gordhun:
Just out of curiosity I looked in the National Map Viewer catalogue for a LiDAR tile at Stanford and then checked the metadata. It says the projection is lambert conformal conic projection.
I don't often have luck with that one but once aced it by pretending it was State Plane and plugging in the state plane zone which in your case is CA_3.
Mar 10, 2021 9:35 PM # 
hughmac4:
You’re UTM 10N, AJ.

https://mangomap.com/robertyoung/maps/69585/what-u...-
Mar 12, 2021 5:53 PM # 
cedarcreek:
Be sure to validate the x and y (eastings and northings, typically) separately from the z (elevation) regarding feet, surveyfeet, and meters. For some reason, I've seen lots of xy in meters and z in feet. I use https://mapper.acme.com/ with the options set to UTM to see the UTM x-y value of the crosshairs (in the middle of the browser window). In the US, you can use the Topo map layer to view 24K, 100K, and 250K map scales. The 24K (zoomed all the way in) are feet elevations, the 100K are meters elevations, and the 250K are back to feet elevations.

If your eastings and northings are both 7-digits, that's an indication they're in feet, but it isn't perfect because west in the "UTM wedge" the values will be 6 digits. UTM northings in meters max out at about 10,000,000m, and in the USA are usually in the 3-5 million range. If you see really big northings, like 9-16 million range, that's probably feet. But a lot of state projections have weird false eastings and northings that give them random values where the only thing you can say is "It doesn't match the expected coordinates for UTM in meters".

It's good to run lasinfo.exe on a file to see any embedded metadata and to see the x y z value ranges, as well as other cool stuff like how many returns and what classifications they have.

I use:

lasinfo -i filename.laz -otxt -cd

but leave off the -cd if you have a lot of files or if you're in a hurry. It calculates point density (points per square meter) as well as post spacing. Post spacing is a weird parameter. I think a post spacing of 4 means 1 return in 16 square meters.
Mar 12, 2021 6:28 PM # 
ajriley:
@gordhun is completely right and that's the same thing Andrea told me by email. Just poorly labelled data is seems like.

Why do they have to make it so confusing...
Mar 12, 2021 11:47 PM # 
gordhun:
You know what is even more frustrating AJ is that at least one staffer with USGS doesn't even acknowledge that there is a problem with the way they are presenting their LiDAR to the market. It is as if they are saying 'hey, it's free. What are you complaining about?'
About six years ago one of my first projects using USGS filed LiDAR was in Sarasota County, Florida. I was really happy to finally being able to get the LiDAR tiles for free, no hassle and I would not have to be tracing contour lines from an old topo map (yes, I've done that plenty of times.)
So the metadata told me the LiDAR was using Transverse Mercator and I told that to OCAD. The first indication of a problem was when OCAD asked me to confirm the coordinates. The next indication was when the contours came in covering about 2 1/2 times (something like that) the area that it should.
So good citizen that I am I reported the problem to USGS - the projection of the tiles were state plane when they were presented as UTM. (I hope you folks understand this).
Expecting a 'thank you for reporting the problem' message back, maybe a medal too, I was taken aback to hear from some functionary saying that "NO all our LiDAR is projected in UTM" To hell with him. So since then it has been a bit of sleuthing and then trial and error to find the proper projection. But the work gets done.
Final advice: if you want to make an orienteering map in the US and want it to go easily make it in Minnesota. Their stuff is great and the UTM system is used for tiles across the state.
Mar 13, 2021 3:56 AM # 
andreais:
MN - haha, yeah, except for the tiles right at the border to SD, which are in UTM 14N, but the rest of the state is zone 15N, and if you process the ones in 14N, and if pulled in together, the tiles at the E end of 14 are pulled up at the E end of 15!! So even MN has its challenges.
Mar 13, 2021 2:33 PM # 
danfoster:
@gordhun and others:

The comments below are offered on the possibility that:
"the projection of the tiles were state plane when they were presented as UTM"
was actually:
"the projection of the tiles were state plane when they were presented as Transverse Mercator"

You could very well have state plane data that is reported by OCAD and others as being in Transverse Mercator, because roughly half of the US state plane projections (including Florida East and Florida West) are based on Transverse Mercator. Almost all of the rest (including Florida North) are in Lambert Conformal Conic.

UTM is Universal Transverse Mercator. It's just a set of 60 (or 120 if you count by hemisphere) standard Transverse Mercator projections covering the entire earth. So UTM is a subset of Transverse Mercator, and half of the US state plane formats are subsets of Transverse Mercator. But having data in Transverse Mercator does not imply UTM or state plane.

There are also versions of both UTM and state plane projections that use US Survey Feet instead of meters as the units. If your data is scaled up or shrunk down by 2.54x, the units aren't being interpreted correctly.

Most GIS data comes with a .prj file (or sometimes now a .xml file) which you can open in a text editor and get the projection information, including the base projection type (Transverse Mercator, Lambert Conformal Conic, Albers), the units (meters, international feet, US survey feet), and the datum.

UTM and State Plane are best thought of not as projections themselves, but as standardized sets of parameters to apply to their base projections. For UTM, that's always Tranverse Mercator, and for State Plane, it's mainly Transverse Mercator or Lambert Conformal Conic, with some Oblique Mercator thrown in for fun in Alaska.
Mar 13, 2021 9:08 PM # 
RickD:
For lidar, I've had good results from the NOAA Data Access Viewer. It lets you choose what projection you want, etc. The general link is:

https://www.coast.noaa.gov/dataviewer/#/

And this looks like the Stanford Dish area:
https://www.coast.noaa.gov/dataviewer/#/lidar/sear...
Mar 13, 2021 10:08 PM # 
cmorse:
NOAA DAV will also let you specify your units (feet vs meters) and do the data conversion on their end.
Mar 13, 2021 11:56 PM # 
gordhun:
NOAA? Thank you very much. I had heard there was a special series/ repository of LiDAR for US coastal areas but never knew where to find it. Never looked too hard either. It looks as if it will fill in some holes in The National Map Viewer's Florida collection. Thanks again.

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