[pdal] Regarding Reprojection Between Vertical Datums

[Nicholas Stanley]

Greetings,

My goal is to reproject/align a third party GRS80 point cloud data 
source to an existing UTM10 WGS84 (EPSG 32610) georeferenced point cloud 
file/"ground truth".

Running Lasinfo on the third party data source (to be 
corrected/reprojected/aligned to Ground Truth) shows the following:


/// 'OGC Transformation Record'//
//    WKT OGC COORDINATE SYSTEM://
//    COMPD_CS["NAD83(2011) / Conus Albers + NAVD88 
height",PROJCS["NAD83(2011) / Conus 
Albers",GEOGCS["NAD83(2011)",DATUM["NAD83 (National Spatial Reference 
System 2011)",SPHEROID["GRS 
1980",6378137,298.257222101,AUTHORITY["EPSG","7019"]],AUTHORITY["EPSG","1116"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","6318"]],PROJECTION["Albers_Conic_Equal_Area"],PARAMETER["standard_parallel_1",29.5],PARAMETER["standard_parallel_2",45.5],PARAMETER["latitude_of_center",23],PARAMETER["longitude_of_center",-96],PARAMETER["false_easting",0],PARAMETER["false_northing",0],UNIT["meter",1,AUTHORITY["EPSG","9001"]],AXIS["X",EAST],AXIS["Y",NORTH],AUTHORITY["EPSG","6350"]],VERT_CS["NAVD88 
height",VERT_DATUM["North American Vertical Datum 
1988",2005,AUTHORITY["EPSG","5103"]],UNIT["meter",1,AUTHORITY["EPSG","9001"]],AXIS["Up",UP],AUTHORITY["EPSG","5703"]]] 
///


I am able to successfully reproject the file in PDAL so that the 
relative 2D alignment in Easting/Northing is corrected - using a command 
like this:

///pdal translate filename.laz filename_utm.laz reprojection 
--filters.reprojection.out_srs="EPSG:32610"///


*Reviewing the output, this shows proper 2D Grid alignment between 
ground truth and third party data, but a delta of ~30M in elevation 
between the ground planes. **This needs to be rectified.
*

*I've recently found this site describing a process to reproject a .las 
file in respect to various vertical datums.*


http://www.gadom.ski/2017/05/31/vdatum-with-pdal.html

///In order to use//PDAL <https://www.pdal.io/>//to convert vertical 
coordinates to a new vertical datum, we’ll need to fetch the appropriate 
geoid. PDAL uses//proj.4 <http://proj4.org/>//under the hood, and proj.4 
accepts geoid’s in NOAA VDatum’s//|gtx|//file format. We can fetch the 
12B geoid from the//VDatum download website 
<https://vdatum.noaa.gov/download.php>//. Inside the 12B zipfile there 
is a file called//|g2012b_conus.gtx|//; this is the geoid for the 
Continental United States (CONUS). We’ll use this file to convert our 
data.///


I've downloaded the VDatum collection as stated - That said, I've been 
unable to get the process to work properly.

///pdal translate filename.laz filename_utm.laz reprojection 
--filters.reprojection.out_srs="+init=EPSG:32610 
+geoidgrids=~/Downloads/vdatum/g2012b_conus.gtx" 
--writers.las.a_srs=EPSG:32610+4326//
//(pdal translate Error) GDAL failure (1) SetCompoundCS() fails, 
vertical component is not VERT_CS.//
//(pdal translate writers.las Error) GDAL failure (1) PROJ: 
proj_crs_get_coordinate_system: Object is not a SingleCRS///


Does anyone have any Tips/Pointers as to how to resolve/debug this issue?

Thanks.
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