[Proj] Verification of inverse step in projection

[Roger Oberholtzer]

On Dec 12, 2009, at 2:44 PM, José Luis García Pallero wrote:

> Hi,
> I'm a new proj user and I have a doubt about the verification of
> inverse step in projection. As the manual says (proj.4.3.pdf, page
> 41):
>
> "Some projections do not have inverse capability; a state that can be
> determined by proj->inv==0."
>
> But when I try to test:
>
> #include<proj_api.h>
> ......
> projPJ pjStruct;

Perhaps:

projPJ *pjStruct;

as pj_init_plus returns a pointer.


> pjStruct = pj_init_plus("+proj=tcc +ellps=clrk66 +lon_0=90W");
> if(!pjStruct)
>    ....
> if(pjStruct->inv==0)
>    ....
>
> At compilation time I obtain the error:
>
> prueba.c: In function ‘main’:
> prueba.c:22: warning: dereferencing ‘void *’ pointer
> prueba.c:22: error: request for member ‘inv’ in something not a
> structure or union
>
> It says that inv is not a member of the projectios struct.
> What is the correct way to check if a projection has inverse step?
>
> Thanks
>
> -- 
> *****************************************
> José Luis García Pallero
> jgpallero at gmail.com
> (o<
> / / \
> V_/_
> Use Debian GNU/Linux and enjoy!
> *****************************************
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Roger Oberholtzer

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