Hi Sebastian,
Perhaps your GPU can use doubles ? Many of them can these days. You may
also try to refactor the code to use pairs of floats (as base and offset)
which in theory may be almost as precise as double. It may be however very
tricky for such non-linear math as geographic projections...
Cheers,
Wojtek
2013/12/5 Sebastian Messerschmidt <sebastian.messerschm...@gmx.de>
> Hi,
>
> I managed to get the local heights.
> After realizing, that the osg_ViewMatrix * gl_ModelViewMatrix will bring
> me into world space I was able to use a XYZ_to_latlonheight function in the
> vertex shader.
> There is only one catch with this: precision. It seems that the float
> matrices will simply cut away to much precision so I get massive flickering.
> Anyone any idea how to solve, improve this? In the end I simply want to
> draw a water surface where the height of the geometry is below a certain
> threshold. My problem here are the fragment where the height is almost
> equal to the threshold.
>
> I also tried to move the LLH-calculation to the fragment shader, but it
> didn't help.
>
> example:
>
> vertex-shader:
>
> out vec3 lat_lon_height;
>
> vec3 XYZ_to_llh(vec3 ws_pos)
> {
> //from osgEarth
> float X = xyz.x;
> float Y = xyz.y;
> float Z = xyz.z;
> float _radiusEquator = 6378137.0;
> float _radiusPolar = 6356752.3142;
> float flattening = (_radiusEquator-_radiusPolar)/_radiusEquator;
> float _eccentricitySquared = 2*flattening - flattening*flattening;
> float p = sqrt(X*X + Y*Y);
> float theta = atan(Z*_radiusEquator , (p*_radiusPolar));
> float eDashSquared = (_radiusEquator*_radiusEquator -
> _radiusPolar*_radiusPolar)/(_radiusPolar*_radiusPolar);
> float sin_theta = sin(theta);
> float cos_theta = cos(theta);
>
> float latitude = atan( (Z +
> eDashSquared*_radiusPolar*sin_theta*sin_theta*sin_theta),
> (p - _eccentricitySquared*_radiusEquator*cos_theta*cos_theta*cos_theta) );
> float longitude = atan(Y,X);
> float sin_latitude = sin(latitude);
> float N = _radiusEquator / sqrt( 1.0 - _eccentricitySquared*sin_
> latitude*sin_latitude);
> float height = p/cos(latitude) - N;
> return vec3(longitude, latitude, height);
> }
>
> void main()
> {
> vec3 ws_pos = osg_ViewMatrix * osg_ModelViewMatrix * gl_Vertex;
> llh = XYZ_to_llh(ws_pos);
> ...
> }
>
> fragment:
>
> void main()
> {
> if (llh.z < 10.0)
> {
> gl_FragColor = vec4(1,0,0,1);
> }
> else
> {
> gl_FragColor = color;
>
> }
> }
>
>
> Hi,
>>
>> I have a osgDEM produced geocentric database.
>> I looked into the geometryTechnique implementation to see if I somehow
>> can access the height of the vertices above the ellipsoid in the vertex
>> shader.
>> Unfortunately I don't have any idea how to calculate this from the give
>> matrices. Is this information somehow available at all?
>> My plan is to overwrite some of the functionality in the
>> geometryTechnique to pass the appropriate matrices to the shader.
>> Anyone having an idea?
>>
>>
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>> http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
>>
>
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