las2las project in county coordinate system?

[Stacey Henk]

Is there a function in LAStools to convert from UTM to a county coordinate system?  I am currently in UTM 16 and need to convert to a county coordinate system

NAD_1983_HARN_WISCRS_Outagamie_County_Feet

Projection: Transverse_Mercator

False_Easting: 802999.999

False_Northing: 0.016

Central_Meridian: -88.5

Scale_Factor: 1.0000286569

Latitude_Of_Origin: 42.71944444444445

Linear Unit: Foot_US (0.3048006096012192)

Geographic Coordinate System: GCS_North_American_1983_HARN

Angular Unit: Degree (0.0174532925199433)

Prime Meridian: Greenwich (0.0)

Datum: D_North_American_1983_HARN

  Spheroid: GRS_1980

    Semimajor Axis: 6378137.0

    Semiminor Axis: 6356752.314140356

    Inverse Flattening: 298.257222101

[Evon Silvia]

I posted a response to a similar question a couple months ago. Looks like you're using a well-defined transverse mercator coordinate system, so las2las should be able to do what you want. Check it out here:

https://groups.google.com/d/msg/lastools/jRV0bvyAlJQ/G0DBNE7qBQAJ

Evon

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[bells.holly]

I see the disclaimer about las2las' projection tag not working for datum transformations. My question is, since WGS84 is not actually a datum, does las2las perform a 7 parameter transformation when I "project" to State Plane (NAD83)? It's not technically going between datums, rather from no datum to a datum. If las2las doesn't perform a 7 parameter transformation, what exactly does it do?

[Martin Isenburg]

Hello,

las2las neither performs datum nor ellipsoid transforms. Whatever datum (or ellipsoid, see Evon's awesome description of how the two are related [1]) your geographic, geocentric, or projected coordinates are on, that is what they will still be on after a "reprojection". In the future I will add a WARNING to las2las when your try to reproject to different datums / ellipsoids. 

What are the typical observed differences / shifts between NAD83, NAD83-HARN, and WGS84 on the ground? 

Regards,

Martin 

[1] http://groups.google.com/d/msg/lastools/Id8fNoABYEI/8Y_q2EFGZBkJ

On Sat, Jun 4, 2016 at 5:59 PM, bells.holly <bells...@gmail.com> wrote:

I see the disclaimer about las2las' projection tag not working for datum transformations. My question is, since WGS84 is not actually a datum, does las2las perform a 7 parameter transformation when I "project" to State Plane (NAD83)? It's not technically going between datums, rather from no datum to a datum. If las2las doesn't perform a 7 parameter transformation, what exactly does it do?

[Nicolas Cadieux]

Hi,
You can also try VDatum software.
Nicolas

[Kirk Waters - NOAA Federal]

In addition to VDatum (vdatum.noaa.gov), you might check out the HTDP program (http://www.ngs.noaa.gov/TOOLS/Htdp/Htdp.shtml). I did write a little blog post on NAD83 versus WGS84 in the vertical if you're interested. The shifts vary spatially, as you might expect.

Kirk Waters, PhD                     | NOAA Office for Coastal Management

Applied Sciences Program      | 2234 South Hobson Ave
843-740-1227                          | Charleston, SC 29405    

coast.noaa.gov/digitalcoast

[Holly Wilkie]

Thanks Kirk, I enjoyed that blogpost very much! 

My projects are small enough that I can get away with using target-derived offsets to perform 3-parameters transformations. The biggest offsets I've seen were in the Western part of the state; x:1.8, y:1.6, z:0.6, roughly, in meters. Up in Santa Fe, it was about 1.5', and in Albuquerque it's around 0.2'. Since the field crew is still working out all the kinks with their mobile RTK, I have to check.

VDatum looks like a good option, and I can't wait to compare the results! 

And finally, I thankfully do not deal with time-tagged survey data :)

[Stacey Henk]

I understand that I will have to account for the geodial seperation using another method outside of LAStools, but I am getting an issue in the X or Y (not sure how to tell which, or both, really) when I reproject.  The data must be shifting a bit, because once i reproject my elevations are not accurate.  Am I missing something? I've attached a file comparing what I entered in las2las and what the parameters are for the coordinate system I'm trying to get to.

Thanks!

Stacey

[Kirk Waters - NOAA Federal]

Stacey,

Can you tell us what you're seeing that indicates the problem (i.e. you know it's wrong because ...)? One thing I notice is that in your original post you showed the target projection had a scale factor greater than 1 and in the screenshot using LAStools, it was less than 1.

Kirk Waters, PhD                     | NOAA Office for Coastal Management

Applied Sciences Program      | 2234 South Hobson Ave
843-740-1227                          | Charleston, SC 29405    

coast.noaa.gov/digitalcoast

[Stacey Henk]

Thanks for the reply, Kurt.  The first parameters were of the HARN projection, which I learned I was not to use.  The second parameters match what our surveyors use.

When I compare my raw lidar points in UTM ellipsoid heights to my truth points in UTM ellipsoid height, the elevation differences are minimal.  After reprojecting the lidar to the county coordinate system I compared the elevations with the truth points that I received from the surveyors in county coordinate system (without applying the geoidal shift to either).  The elevation differences are now more significant.  For example, one truth point compared to the lidar was off 0.016 meters.  After projecting, it was off 0.5 feet.  To me, this would suggest that the data is being shifted.

[Kirk Waters - NOAA Federal]

The original ground truth and data were in WGS84, right? If that's true, it could be the shift of datums. On the other hand, Survey monuments and COR stations are generally NAD83. 

On Friday, June 17, 2016, Stacey Henk <stace...@gmail.com> wrote:

Thanks for the reply, Kurt.  The first parameters were of the HARN projection, which I learned I was not to use.  The second parameters match what our surveyors use.

When I compare my raw lidar points in UTM ellipsoid heights to my truth points in UTM ellipsoid height, the elevation differences are minimal.  After reprojecting the lidar to the county coordinate system I compared the elevations with the truth points that I received from the surveyors in county coordinate system (without applying the geoidal shift to either).  The elevation differences are now more significant.  For example, one truth point compared to the lidar was off 0.016 meters.  After projecting, it was off 0.5 feet.  To me, this would suggest that the data is being shifted.

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[Holly Wilkie]

Stacey, is the difference consistent or does it vary from truth point to truth point?

What software do you use to project the survey points from the county coordinate system to UTM? 

On Jun 17, 2016, at 3:07 PM, Stacey Henk <stace...@gmail.com> wrote:

Thanks for the reply, Kurt.  The first parameters were of the HARN projection, which I learned I was not to use.  The second parameters match what our surveyors use.

When I compare my raw lidar points in UTM ellipsoid heights to my truth points in UTM ellipsoid height, the elevation differences are minimal.  After reprojecting the lidar to the county coordinate system I compared the elevations with the truth points that I received from the surveyors in county coordinate system (without applying the geoidal shift to either).  The elevation differences are now more significant.  For example, one truth point compared to the lidar was off 0.016 meters.  After projecting, it was off 0.5 feet.  To me, this would suggest that the data is being shifted.

--

[Nicolas Cadieux]

Hi,

I lost the beginning of this conversation but are both CRS using the same ellipsoid? One could be wgs84 and one GSR80.

Nicolas

[Stacey Henk]

The ground truths are in NAD 83.  So if my lidar is WGS, should I be using the VDatum to solve?  What kind of shifts would I expect if this were the issue (would it vary across a singe project, stretching north to south 0.5 miles)?  Comparing point to point for example, I had a shift of 0.422 feet further north, and a shift of 0.35 feet further south.  

Stacey

[Nicolas Cadieux]

Hi,

I have not used vdatum yet.  You may have to do horizontal transformation first and the then a vertical transformation to get to the correct geoid.  I do not know if vDatum does both.  Keep in mind that there are many versions of nad83 and many version of wgs84.  Google that with "confluence" and you should find a few good article on the subject.

You can expect up to 2m difference hoz and probably around 50cm vertically between systems. You can find many online calculator to check.  Differences should be relatively smooth across the project.

Personally, I use gps-h and trx software from nrcan to do those transformations.  They will handle US geoids but not .las files currently.  I use las2txt then a Python code to to the job as gps-h will strip some columns.  I think vdatum can directly handle the .las files.

Nicolas

[Kirk Waters - NOAA Federal]

Vdatum will do the transform in 3D. As Nicolas points out, there are many versions of WGS84 and NAD83. I think in Stacey's area, the vertical shift is about 3 feet between the ellipsoids (NAD83(2011) is around 3 feet where WGS84(G1150) is zero feet). I expect the shift values wouldn't change noticeably for a half mile stretch. How sure are you that the lidar is in WGS84 vertically though? It would be rare to get WGS84 ellipsoid heights if it was commercially collected (a research project might though). Being in UTM doesn't mean it's WGS84 (horizontally or vertically).

Kirk Waters, PhD                     | NOAA Office for Coastal Management

Applied Sciences Program      | 2234 South Hobson Ave
843-740-1227                          | Charleston, SC 29405    

coast.noaa.gov/digitalcoast