Finding the correct viewing position

Step 1: Decide whether there are any lines representing lines orthogonal to the picture plane:

Example of how to decide:

Consider the box shown below. The front panel is an actual rectangle -- that is, it consists of two pairs of lines that are parallel in the image.

What direction do parallel lines in the real world need to be heading in, to be drawn parallel in the image?

Lines which are parallel to the picture plane!

Assuming that the thing above that looks like a box really is a box, then from our knowledge of boxes, we can conclude that the sides of the box are orthogonal to the picture plane.

Because of that, we know that the lines in the box represent lines which are orthogonal.

Once you know that there are lines orthogonal to the picture plane, you know to put your eye directly opposite the vanishing point.

But ...how far back?

Next!

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