[OSGeo-Discuss] Parsing well-known text

[Even Rouault]

Pierre,

> I just added code to PerfectTIN to read the variable-length records of a LAS
> file. I found a WKT record in a square of West Virginia terrain, with no
> line feeds; I added line feeds and indentation and attached it. The other
> point clouds do not have variable-length records. I'd like to heed the WKT
> units when loading a point cloud, if there is a WKT.
> 
> I'm also working on a program called Wolkenbase (not public yet) which will
> separate ground from non-ground in a point cloud. If you load a point cloud
> with no unit information, I'd like to add a WKT that indicates only the unit
> and nothing else. What would that look like?

As far as I know, you can't create a CRS WKT with just unit information. The most minimal 
content that validates the WKT1 grammar would be something like:

LOCAL_CS["unspecified CRS",
    LOCAL_DATUM["unspecified datum",2000],
    UNIT["metre",1,
        AUTHORITY["EPSG","9001"]],
    AXIS["Easting",EAST],
    AXIS["Northing",NORTH]]

> Do you have code to parse and manipulate WKT? The WKT is in a std::string.

Yes, PROJ >= 6 has support for parsing and creating WKT in several versions of the WKT 
standard.

See proj_create_from_wkt() at https://proj.org/development/reference/functions.html, and 
all other proj_XXXX getters.

For creation of WKT, you might need the more advanced functions of 
https://github.com/OSGeo/PROJ/blob/master/src/proj_experimental.h , before exporting 
with proj_as_wkt()

GDAL's OGRSpatialReference class showcases using number of the above mentionned PROJ 
functions:
https://github.com/OSGeo/gdal/blob/master/gdal/ogr/ogrspatialreference.cpp


You may also look at PDAL that uses PROJ and/or GDAL underneath to deal with LAS CRS:
https://pdal.io/tutorial/las.html#spatial-reference-system


Even

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