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yanasdf789
07-23-2013, 01:24 AM
in Three-dimensional space， i know the positon of camera and Target point，how to Calculate the Irradiated area on Plane with z=0?

thokra
07-23-2013, 02:06 AM
What irradiated area? Do you want to know how large the visible area of the xy-plane (z = 0) is?

yanasdf789
07-25-2013, 03:02 AM
What irradiated area? Do you want to know how large the visible area of the xy-plane (z = 0) is?

yes!! how can i do it ?

yoyonel
07-25-2013, 05:13 AM
yes!! how can i do it ?
lol it's a joke yanasdf789 ;)
The xy-plane(z=0) is infinite, like all planes of "space" (dimension(s) >= 1).

yoyonel
07-25-2013, 05:17 AM
Irradiated area on Plane with z=0 ... mmmMMMmm ...
you want to compute the area of the projection of the xy-plane (z=0) on the near plane of your camera ?

thokra
07-25-2013, 05:24 AM
Irradiated area on Plane with z=0 ... mmmMMMmm ... you want to compute the area of the projection of the xy-plane (z=0) on the near plane of your camera ?

Hence the term "visible" ... The OP wants to know how large the visible area of the XY plane is - depending on the current parameters of the camera.

yanasdf789: is your camera always orthogonal to the plane or not?

yanasdf789
07-29-2013, 01:29 AM
Hence the term "visible" ... The OP wants to know how large the visible area of the XY plane is - depending on the current parameters of the camera.

yanasdf789: is your camera always orthogonal to the plane or not?
if I know the the current parameters of the camera and camera always orthogonal to the plane,how to compute the area of the projection of the xy-plane (z=0)

GClements
07-29-2013, 06:37 AM
if I know the the current parameters of the camera and camera always orthogonal to the plane,how to compute the area of the projection of the xy-plane (z=0)
For a centred perspective projection:

The height is 2 * camera_z * tan(fovy/2)
The width is 2 * camera_z * tan(fovy/2) * aspect
The area is (2 * camera_z * tan(fovy/2))2 * aspect.

Where camera_z is the Z coordinate of the camera's position, and fovy and aspect are the corresponding parameters to the gluPerspective() call.

For a generalised perspective projection:

The height is (top - bottom) * camera_z / nearVal
The width is (right - left) * camera_z / nearVal
The area is (right - left) * (top - bottom) * (camera_z / nearVal)2

where camera_z is the Z coordinate of the camera's position, and the other variables are the corresponding parameters to the glFrustum() call.