Hi Wojciech,
Hi Sebastian,
Just an extra thought that came to me. Terrain LOD paging may cause
the elevation jumps too. When LODs change meshes get denser or less
dense - new vertices show up or excess vertices hide and that may also
bring lot of surprises.
You're correct. But it seems to happen mostly if get close to the mesh,
where the LOD should not change anymore.
Right now I'm trying to live with it. But I'm sure there might be clever
tricks to make it nicer ;-)
I'm trying to get some info from the osgEarth guys, they surely know how
to handle those floating point beasts.
cheers
Sebastian
Cheers,
Wojtek
2013/12/5 Wojciech Lewandowski <w.p.lewandow...@gmail.com
<mailto:w.p.lewandow...@gmail.com>>
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
<mailto: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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