--nologdepth leads to culling of near features

[rebmaso]

Hello,

I'm trying to solve the problem I outlined in issue #2366 , where @gwaldron and @timoore suggested to use the --nologdepth flag in order to get a nonlinear depth buffer (rather than a logarithmic one).

Although it looks like this solves my original problem (not sure yet, though), a new one is raised: when camera plane is orthogonal to the ground (or close to this condition), I lose a lot of content, as shown in pic.
I assume this is due to the fact that in this condition there are features that are in the frustum and have very low depth.

I tried messing with the near clip plane in the projection matrix but that changes nothing.

Question: Is there any way to both visualize close features AND use --nologdepth?

For reference, this is how I set the Projection matrix. It's as if it does not matter which near - far values I use.

double cx = MY_OSG_WIDTH / 2.; //principal point x coord
double cy = MY_OSG_HEIGHT / 2.; //principal point y coord
double w = MY_OSG_WIDTH; //image width
double h = MY_OSG_HEIGHT; //image height
double near = 0.01; //near plane
double far = 10.0; //far plane
double f = 480.; // focal length in px (assume fx=fy)

// Projection matrix
osg::Matrixd K_gl(2*f/w, 0.0, (w - 2*cx)/w, 0.0,
                    0.0, 2*f/h, (h - 2*cy)/h, 0.0,
                    0.0, 0.0, (-far - near) / (far - near), -2.0*far*near/(far-near),
                    0.0, 0.0, -1.0, 0.0);

osg::Matrixd projMatrix;
projMatrix.transpose(K_gl);

// setComputeNearFarMode setting breaks everything (far plane is very close: very nearsighted)
// viewer.getCamera()->setComputeNearFarMode(osg::CullSettings::DO_NOT_COMPUTE_NEAR_FAR);
viewer.getCamera()->setProjectionMatrix(projMatrix);

// I get same results setting like this, messing with near and far
// double fov = 2.0*atan( 1.0/projMatrix(1,1) ) * 180.0 / M_PI;
// double aspect = projMatrix(1,1) / projMatrix(1,1);
// viewer.getCamera()->setProjectionMatrixAsPerspective(fov, aspect, near, far);

Here are two screenshot of the viewport at the same view point, with and without the logarithmic depth buffer, respectively:

[gwaldron]

I think you misunderstood. I was merely suggesting using --nologdepth to test the LDB theory, not to solve your problem.

If you disable the LDB, you do need to either
(a) Use DO_NOT_COMPUTE_NEAR_FAR and set the clip planes manually; or
(b) Use osg::Camera::setNearFarRatio to pull the near plane closer to the camera. (This is why your attempt to set the near plane failed - it is auto-calculated by multiplying the far plane by this ratio.)

Otherwise, you will need to reverse-engineer the LDB projection matrix. The shader that applies it is here:
https://github.com/gwaldron/osgearth/blob/master/src/osgEarth/LogDepthBuffer.VertOnly.glsl

[rebmaso]

solution a) solved the culling problem without LDB : viewer.getCamera()->setComputeNearFarMode(osg::CullSettings::DO_NOT_COMPUTE_NEAR_FAR);