distance to projection plane and coordinates per pixel
How can I get the distance from a point p to the projection plane?
Is there any way to calculate the numbers of pixels per world coordinate unit in the screen x-y coordinate system?
Well if point p is in camera or eye coordinates then I think the distance from p to the near projection plane would be the z-component of p minus the near projection plane distance.
I'm not sure exactly what your asking in your second question though. I can give you a formula for finding near projection plane coordinates based on camera coordinates.
projection plane x = (N * p.x)/-p.z
projection plane y = (N * p.y)/-p.z
Where N is the near projection plane distance I was talking about in the answer to the first part of your question, it's the second to last parameter in gluPerspective or glFrustum. I use -p.z because p.z is negative in camera coordinates anyway and I just need the absolute value for z. The larger the value of z or the greater the distance from the camera, the smaller the value of x and y on the projection plane aka perspective foreshortening. There is still another step before these are screen coordinates though, mainly how you called glViewport.
I'm not sure exactly what your asking in your second question though. I can give you a formula for finding near projection plane coordinates based on camera coordinates.
projection plane x = (N * p.x)/-p.z
projection plane y = (N * p.y)/-p.z
Where N is the near projection plane distance I was talking about in the answer to the first part of your question, it's the second to last parameter in gluPerspective or glFrustum. I use -p.z because p.z is negative in camera coordinates anyway and I just need the absolute value for z. The larger the value of z or the greater the distance from the camera, the smaller the value of x and y on the projection plane aka perspective foreshortening. There is still another step before these are screen coordinates though, mainly how you called glViewport.
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