Direction of Projection

[Ken Martin]

At 07:21 AM 5/3/00 -0400, you wrote:
>Folks,
>         I talked to Jim Miller about the Direction of Projection in the 
> camera. His first reaction
>was" DOP is only used for parallel projections." Sure enough, I checked 
>Foley and vanDam (pg 231, top
>paragraph).
>
>Should we revisit this?

Again I don't have Foley vanDam here.  But I don't see how this changes 
anything. We don't use DOP in perspective projections, we use VPN, but... 
-DOP still is not the same as VPN. If you want to keep using VPN that is 
fine, but it is not the vector between the camera position (PRP or COP I 
believe) and the focal point (VRP). Maybe what we want is a boolean 
indicating (assume VPN is -DOP) which is was what the (3 years or so ago) 
old code did (but without the boolean). But that is confusing because the 
shears being introduced are there to handle the case where VPN != -DOP. 
With the shear angles set, a call to GetVPN that returns -DOP will be 
misleading.

- Ken