[PROJ] Transforming coordinates in C++

[Even Rouault]

Le 29/10/2021 à 13:49, Javier Jimenez Shaw a écrit :
> Thanks Even.
>
> I see that proj_create takes a PJ_CONTEXT *ctx as the first argument. 
> What I have in C++ is a DatabaseContextPtr. Can I get a PJ_CONTEXT* 
> from a DatabaseContextPtr?

I don't see a getter for it currently.  It can be optionally passed in 
the DatabaseContext::create() factory method (DatabaseContext doesn't 
strictly require a PJ_CONTEXT*. From what I can see it is only needed to 
find proj.db and grid files, and if none is provided the default context 
is used. I hope this is safe enough in multi threaded uses. hum...), so 
if there was one, you already knew it through other means, but it 
wouldn't hurt if you added a getter. Or you create one from scratch.  
All this is a testimony of the ISO-19111 part having being mostly 
developed as an addition besides the traditional C code base, and the 
connection between the two parts being a bit tricky.


> .___ ._ ..._ .. . ._. .___ .. __ . _. . __..  ... .... ._ .__
> Entre dos pensamientos racionales
> hay infinitos pensamientos irracionales.
>
>
>
> On Fri, 29 Oct 2021 at 12:17, Even Rouault <even.rouault at spatialys.com 
> <mailto:even.rouault at spatialys.com>> wrote:
>
>
>     Le 29/10/2021 à 12:00, Javier Jimenez Shaw a écrit :
>>     Hi
>>
>>     Using C++ I am trying this: Given two CRSs, I would like to have
>>     access to the list of possible transformations (like with
>>     projinfo), and use those transformations to transform coordinates
>>     (like with cs2cs).
>>
>>     Studying the code of projinfo, that uses mainly the C++ API, I
>>     already have a std::vector<CoordinateOperationNNPtr>. Nice, I can
>>     dump them in different formats.
>>
>>     However, when I go to the code of cs2cs, I see that it is mainly
>>     using the C API.
>>
>>     Is there any C++ equivalent to the function
>>     PJ_COORD proj_trans (PJ *P, PJ_DIRECTION direction, PJ_COORD coord);
>>     ?
>
>     No.
>
>     If you know which transformation you want to do, what you can
>     easily do is exportToPROJString() it, and use proj_create() to
>     instanciate it as a PJ* object you can use with proj_trans()
>
>     That's more or less what proj_create_operations() +
>     proj_list_get() do.
>
>     Even
>
>>
>>     Thanks.
>>     .___ ._ ..._ .. . ._.  .___ .. __ . _. . __..  ... .... ._ .__
>>     Entre dos pensamientos racionales
>>     hay infinitos pensamientos irracionales.
>>
>>
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