Re: [Plib-users] (no subject)

[steve <sjb...@ai...>]

Hemalatha Sharma wrote:
>  
> Hi,
> I am mailing again.
> There was no reply for my query.

All four(!) copies of your email arrived simultaneously - you
need to exhibit some more patience.

> I need to convert from geodetic data to screen coordinates.
> How can i do it?
> 
> There is a function in SimGear(SgGeodToCart) which converts geodetic 
> lat,long to cartesian form.
> But How do i convert from catesian to screen cartesian form.

Geodetic to cartesian is definitely not a PLIB thing - so you're
right to seek help in SimGear.

Cartesian to screen coordinates is probably best handled by the
OpenGL function 'gluProject'...so this isn't really a PLIB question
either.  However:

GLint gluProject ( GLdouble objX, GLdouble objY, GLdouble objZ,
                    const GLdouble *model,
                    const GLdouble *proj,
                    const GLint *view,
                    GLdouble* winX, GLdouble* winY, GLdouble* winZ);

Where:

   (objX, objY, objZ) is the cartesian coordinate you are
                      concerned about.
   model, proj        are the OpenGL modelview and projection matrix.
                      You can either get these by doing a glGetMatrix()
                      or inside SSG you can use
                      ssgContext::getProjectionMatrix()
                      and ssgContext::getModelviewMatrix().
   view               is an array containing the viewport parameters.
                      You get this with glGetFloatv(GL_VIEWPORT,...).
   (winX, winY, winZ) are pointers to where you'd like the return
                      results placed.