Estimating position of occluded 4th corner?

I’m sure this happens a lot… where you have a surface to replace and you can only see 3 of the 4 corners for a corner pin? The 4th corner is never in camera view for the length of the shot.

Is there some handy tip to estimate the position of the hidden 4th corner when using the Show Planar Surface tool? I’ve just eyeballed it until now. But it seems like there should be some mathematical constraints to give an educated guess where the hidden corner might be?

This is quite a difficult problem, as the corner position can vary greatly on the movement of the plane. For example, if the plane is tilting up and away, a corner may actually be shifting far from the other points and look wrong to an algorithm that was trying to keep all the corners neatly together.
It’s certainly a challenge that would be interesting to surmount though, so we’ll add it as a feature request. :slight_smile:

In the AdjustTrack module we use something called Reference Points to help with problems like this. It doesn’t help your exact situation (where it is out of view all the time), but reference points let you select another point nearby to the corner you can’t see and adjust the surface based on that point instead, offsetting the corner.

For eyeballing it, the best way is to use the grid and try to converge on the perpendicular lines to get the corner in the right spot.

Thanks for the advice. Using the grid is a great tip!