Re: [gdal-dev] OGRCreateCoordinateTransformation()

Thu, 24 Mar 2022 08:50:40 -0700 

Steve,

(adding proj mailing list since it's actually purely a PROJ topic
Does the fact that there isn’t a consensus mean 3126 & 3127 aren’t going to end up in a PROJ release?
Did you try them to confirm they help ? Maybe if you want to weight in the PRs (if they actually help) that could change the balance.
I read through the PR’s. Are you thinking my issue is that a vertical shift is being introduced because of a transformation to WGS84 (from NAD83(CSRS)) to look up the geoid separation value?
That's probably an issue with the wrong interpolation CRS being used, but I can't generally predict how this complex code works without launching a debugger and step-by-step tracing what happens.
PROJ4_GRIDS provided a way to specify exactly which geoid file(s) to use.  Some vertical datums, such as NAVD88, only have a single EPSG code for multiple geoids – what’s the replacement for PROJ4_GRIDS in PROJ9?  If I could switch to WKT2 strings (not sure that’s really feasible) does it fix these problems?
WKT2 hardly helps for that. The closest equivalent is the GEOIDMODEL[] sub node of a VERTCRS[] (http://docs.opengeospatial.org/is/18-010r7/18-010r7.html#83). But that's something that refer to an existing transformation . And in a VRTCRS[] you can actually have several GEOIDMODEL[] listed (e.g. for NAVD88, all the geoid models), since that's more a definition of the VertCRS than which particular geoid model to use. So that's not nominally appropriate for a "random" grid not known of PROJ, although we have a bit bent the concept to allow a GEOIDMODEL["PROJ name_of_the_grid_dot_tif_or_gtx"]. But I would suspect that in that situation the ambiguity with the geographic / interpolation CRS to use would be similar to WKT1 PROJ4_GRIDS. 

Thanks,

steve

*From:* Even Rouault <even.roua...@spatialys.com>
*Sent:* Wednesday, March 23, 2022 6:06 PM
*To:* Steve Riddell <sridd...@geocue.com>; gdal-dev@lists.osgeo.org
*Subject:* Re: OGRCreateCoordinateTransformation()

Steve,
you may try PR https://github.com/OSGeo/PROJ/pull/3126 or https://github.com/OSGeo/PROJ/pull/3127, that might potentially help, but they don't make consensus (see discussions of those PRs). Basically it is a nightmare to deal with the old TOWGS84 / PROJ4_GRIDS approach, that poorly specifies some elements of transformations (especially the vertical part), and doesn't fit well in the ISO-19111 model used by newer PROJ (we use and abuse the BoundCRS approach in complex ways). One of the issue too is that we've realized late in the process that we didn't emulate some aspects of the old transformation pipeline, and there isn't general enthusiasm to change that now. 

Even

Le 23/03/2022 à 23:42, Steve Riddell a écrit :

    Hi Even,

    I tried the fix with the CRS’s I sent, and it worked. But as I
    mentioned, my real target CRS is a custom projected system
    (below), and it still fails with what seems to be the same error
    as in my original email.

    COMPD_CS["TempTM + CGVD28 height - HT2_0",

        PROJCS["Custom",

            GEOGCS["NAD83(CSRS)",

    DATUM["NAD83_Canadian_Spatial_Reference_System",

                    SPHEROID["GRS 1980",6378137,298.257222101,

    AUTHORITY["EPSG","7019"]],

                    TOWGS84[0,0,0,0,0,0,0],

    AUTHORITY["EPSG","6140"]],

                PRIMEM["Greenwich",0,

    AUTHORITY["EPSG","8901"]],

    UNIT["degree",0.0174532925199433,

    AUTHORITY["EPSG","9122"]],

                AUTHORITY["EPSG","4617"]],

    PROJECTION["Transverse_Mercator"],

    PARAMETER["latitude_of_origin",49.351346659616],

    PARAMETER["central_meridian",-123.20266499149],

            PARAMETER["scale_factor",1],

    PARAMETER["false_easting",15307.188],

    PARAMETER["false_northing",6540.975],

            UNIT["Meters",1],

            AXIS["Easting",EAST],

            AXIS["Northing",NORTH]],

        VERT_CS["CGVD28 height - HT2_0",

            VERT_DATUM["Canadian Geodetic Vertical Datum of 1928",2005,

    EXTENSION["PROJ4_GRIDS","HT2_0.gtx"],

                AUTHORITY["EPSG","5114"]],

            UNIT["metre",1,

                AUTHORITY["EPSG","9001"]],

            AXIS["Gravity-related height",UP],

            AUTHORITY["EPSG","5713"]]]

    Experimenting, I removed the “TOWGS84” directive from BOTH the
    source and target systems, and I do get an answer instead of an error:

    For test point: (49.351346658, -123.202664992, 289.809)

    I get: (15307.1880,6540.9748,307.744)

    But since geoid separation at the test point is -18.238, Z should
    be 308.047.  In fact, if I code up the following pipeline and
    initialize a transform object:

    strPipe ="+proj=pipeline\

            +step +proj=axisswap +order=2, 1\

            +step +proj=unitconvert +xy_in=deg +xy_out=rad\

            +step +inv +proj=vgridshift +grids=HT2_0.gtx +multiplier=1\

            +step +proj=tmerc +lat_0=49.351346659616
    +lon_0=-123.20266499149 +k=1\

            +x_0=15307.188 +y_0=6540.975 +ellps=GRS80";

    The call to Transform() gives: (15307.1880, 6540.9748, 308.042)  
    -- XY matches above, but now I get the expected Z (-0.005).
     However, I’d like to avoid assembling pipelines for every
    conversion/transform.

    Any arrows left in your quiver?

    Thanks,

    Steve

    *From:* Steve Riddell
    *Sent:* Friday, March 18, 2022 6:17 PM
    *To:* Even Rouault <even.roua...@spatialys.com>
    <mailto:even.roua...@spatialys.com>; gdal-dev@lists.osgeo.org
    *Subject:* RE: OGRCreateCoordinateTransformation()

    Thanks very much, Even.  For reporting the problem, I “packaged
    up” a case with CRS’s with EPGS codes. For the actual problem I’m
    working, the target CRS is a custom projection –no EPSG.

    *From:* Even Rouault <even.roua...@spatialys.com>
    *Sent:* Friday, March 18, 2022 5:05 PM
    *To:* Steve Riddell <sridd...@geocue.com>; gdal-dev@lists.osgeo.org
    *Subject:* Re: OGRCreateCoordinateTransformation()

    Steve,

    Fix in PROJ queued in https://github.com/OSGeo/PROJ/pull/3123

    The complexity of dealing with legacy features TOWGS84[] and
    PROJ4_GRIDS is highly stressing PROJ pipeline computation engine.

    Using the plain EPSG codes  EPSG:4955 -> EPSG:4617+5713 would be
    much preferable here

    Even

    Le 18/03/2022 à 21:14, Steve Riddell a écrit :

        Hi,

        I’m getting an error (below) using GDAL trying to set up a
        transformation between NAD83(CSRS) geodetic, w/ ellipsoidal
        heights, and NAD83(CSRS) geodetic, CGVD28 heights. Similar
        transformations work fine on some datums,  but fail on others.
         Hope someone can offer some insight.  Note the if I don't use
        the PROJ4_GRIDS extension, I don't get the error, but I don't
        get the geoid adjustment either.

        COMPD_CS["NAD83(CSRS) + Ellipsoid (Meters)",

            GEOGCS["NAD83(CSRS)",

        DATUM["NAD83_Canadian_Spatial_Reference_System",

                    SPHEROID["GRS 1980",6378137,298.257222101,

        AUTHORITY["EPSG","7019"]],

                    TOWGS84[0,0,0,0,0,0,0],

                    AUTHORITY["EPSG","6140"]],

                PRIMEM["Greenwich",0,

                    AUTHORITY["EPSG","8901"]],

        UNIT["degree",0.0174532925199433,

                    AUTHORITY["EPSG","9122"]],

                AUTHORITY["EPSG","4617"]],

            VERT_CS["Ellipsoid (Meters)",

                VERT_DATUM["Ellipsoid",2002],

                UNIT["metre",1,

                    AUTHORITY["EPSG","9001"]],

                AXIS["ellipsoidal height",UP]]]

        COMPD_CS["NAD83(CSRS) + CGVD28 height - HT2_0",

            GEOGCS["NAD83(CSRS)",

        DATUM["NAD83_Canadian_Spatial_Reference_System",

                    SPHEROID["GRS 1980",6378137,298.257222101,

        AUTHORITY["EPSG","7019"]],

                    TOWGS84[0,0,0,0,0,0,0],

                    AUTHORITY["EPSG","6140"]],

                PRIMEM["Greenwich",0,

                    AUTHORITY["EPSG","8901"]],

        UNIT["degree",0.0174532925199433,

                    AUTHORITY["EPSG","9122"]],

                AUTHORITY["EPSG","4617"]],

            VERT_CS["CGVD28 height - HT2_0",

                VERT_DATUM["Canadian Geodetic Vertical Datum of
        1928",2005,

        EXTENSION["PROJ4_GRIDS","HT2_0.gtx"],

                    AUTHORITY["EPSG","5114"]],

                UNIT["metre",1,

                    AUTHORITY["EPSG","9001"]],

                AXIS["Gravity-related height",UP],

                AUTHORITY["EPSG","5713"]]]

        ERROR 6: Cannot find coordinate operations from `EPSG:4955' to
        `COMPOUNDCRS["NAD83(CSRS) + CGVD28 height -
        HT2_0",BOUNDCRS[SOURCECRS[GEOGCRS["NAD83(CSRS)",DATUM["NAD83
        Canadian Spatial Reference System",ELLIPSOID["GRS
        
1980",6378137,298.257222101,LENGTHUNIT["metre",1]]],PRIMEM["Greenwich",0,ANGLEUNIT["degree",0.0174532925199433]],CS[ellipsoidal,2],AXIS["geodetic
        latitude
        
(Lat)",north,ORDER[1],ANGLEUNIT["degree",0.0174532925199433]],AXIS["geodetic
        longitude
        
(Lon)",east,ORDER[2],ANGLEUNIT["degree",0.0174532925199433]],ID["EPSG",4617]]],TARGETCRS[GEOGCRS["WGS
        84",DATUM["World Geodetic System 1984",ELLIPSOID["WGS
        
84",6378137,298.257223563,LENGTHUNIT["metre",1]]],PRIMEM["Greenwich",0,ANGLEUNIT["degree",0.0174532925199433]],CS[ellipsoidal,2],AXIS["latitude",north,ORDER[1],ANGLEUNIT["degree",0.0174532925199433]],AXIS["longitude",east,ORDER[2],ANGLEUNIT["degree",0.0174532925199433]],ID["EPSG",4326]]],ABRIDGEDTRANSFORMATION["Transformation
        from NAD83(CSRS) to WGS84",METHOD["Position Vector
        transformation (geog2D
        domain)",ID["EPSG",9606]],PARAMETER["X-axis
        translation",0,ID["EPSG",8605]],PARAMETER["Y-axis
        translation",0,ID["EPSG",8606]],PARAMETER["Z-axis
        translation",0,ID["EPSG",8607]],PARAMETER["X-axis
        rotation",0,ID["EPSG",8608]],PARAMETER["Y-axis
        rotation",0,ID["EPSG",8609]],PARAMETER["Z-axis
        rotation",0,ID["EPSG",8610]],PARAMETER["Scale
        difference",1,ID["EPSG",8611]]]],BOUNDCRS[SOURCECRS[VERTCRS["CGVD28
        height - HT2_0",VDATUM["Canadian Geodetic Vertical Datum of
        1928"],CS[vertical,1],AXIS["gravity-related
        
height",up,LENGTHUNIT["metre",1]],ID["EPSG",5713]]],TARGETCRS[GEOGCRS["WGS
        84",DATUM["World Geodetic System 1984",ELLIPSOID["WGS
        
84",6378137,298.257223563,LENGTHUNIT["metre",1]]],PRIMEM["Greenwich",0,ANGLEUNIT["degree",0.0174532925199433]],CS[ellipsoidal,3],AXIS["latitude",north,ORDER[1],ANGLEUNIT["degree",0.0174532925199433]],AXIS["longitude",east,ORDER[2],ANGLEUNIT["degree",0.0174532925199433]],AXIS["ellipsoidal
        
height",up,ORDER[3],LENGTHUNIT["metre",1]],ID["EPSG",4979]]],ABRIDGEDTRANSFORMATION["CGVD28
        height - HT2_0 to WGS84 ellipsoidal
        height",METHOD["GravityRelatedHeight to
        Geographic3D"],PARAMETERFILE["Geoid (height correction) model
        file","HT2_0.gtx",ID["EPSG",8666]]]]]'


        Thanks in advance for any assistance!

        Best regards,

        Steve

        Steve Riddell

        Software Engineering

        *GeoCue Group, Inc.*

        520 6th Street | Madison, AL 35756 USA

        *Phone:*256.461.8289 | *Fax:* 256.461.8249

        /LIDAR/Drone Mapping Software & Services //– True View® 3D
        Imaging Sensors //–Image/LIDAR Data Management Solutions/

        www.geocue.com <http://www.geocue.com/>support.geocue.com
        <https://support.geocue.com/>
-- 
    http://www.spatialys.com

    My software is free, but my time generally not.

--
http://www.spatialys.com
My software is free, but my time generally not.


--
http://www.spatialys.com
My software is free, but my time generally not.

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