Constructing a Square in 2-Point Perspective

1. Set up a perspective grid with vanishing points 90° apart from each other relative to the station point.

2. Add the diagonal vanishing point by drawing a line at 45° to the lines extending from the station point to the right and left vanishing points.

3. Define 3 sides of the square by drawing 3 lines that intersect with 2 of the lines going to one vanishing point and the remaining line receding to the other vanishing point.

4. Draw a line from one corner of the square through the interior of the square to the diagonal vanishing point.

5. Draw the line from the other vanishing point through the point where the line to the DVP intersects the 3rd line that defines the square.

This last edge of the shape is placed such that it forms a square in perspective.