[PROJ] Way to transform coordinates given an osgeo::proj::operation::CoordinateOperation?

[Even Rouault]

On mercredi 9 octobre 2019 15:47:26 CEST Martin Desruisseaux wrote:
> Hello
> 
> I'm trying to find the best way to transform coordinate tupples given an
> osgeo::proj::operation::CoordinateOperation instance. My current
> understanding is that I need to get a PJ object as below. Is that correct?
> 
>     CoordinateOperationNNPtr operation = ...
>     PJ_CONTEXT *ctx = ...
>     PJ *pj = (ctx, operation);
>     // Then use PJ as documented in "getting started" guide.
> 
> If above is the right approach, looking at the source code of
> pj_obj_create, there is two things I would like to do differently:
> 
>   * Use an existing osgeo::proj::io::DatabaseContext instance.
>   * Do not fallback on pj_new() if the main block could not create the PJ.
> 
> So would the following block be okay (I know if use an internal method
> call, but I didn't saw a way to avoid it yet):
> 
>     DatabaseContext dbContext = ...;
>     auto formatter =
> PROJStringFormatter::create(PROJStringFormatter::Convention::PROJ_5,
> dbContext); auto projString = coordop->exportToPROJString(formatter.get());
> PJ *pj = pj_create_internal(ctx, projString.c_str());
>     // Done; do not touch to pj->iso_obj or pj->cpp_context.
> 
> Or is there a better way to "execute" a CoordinateOperation with C++ API?

You have indeed to go to the C API, but use proj_create() instead of 
pj_create_internal()

-- 
Spatialys - Geospatial professional services
http://www.spatialys.com