Tip 77: Using Lines to Mark Hidden Corners in Photogrammetry

We have a short and sweet tip video this week.

In photogrammetry we often mark the corners of objects in photos to define their 3D locations or outline the object. Did you know that you can use temporary intersecting lines to mark corner points that are obscured or hidden? When modeling buildings, other outdoor scenes/objects, or even indoor rooms, key corners may be obscured (such as by foliage outdoors or furniture indoors).  Here’s a trick to work around the problem. 

By marking temporary lines you can reliably locate the hidden corner in a photo, provided you can align with edges leading to the hidden corner.

In the tip video below, a room is being modeled and a speaker blocks a key corner feature that is to be used to define the shape. Temporary points and lines are marked along the baseboards. These guide points and lines are adjusted to fit and where they intersect a point can be marked.  The temporary lines and points can then be deleted, leaving just the corner point to be referenced on other photos.

To make the point 3D, the corner point is marked (on a visible point or using the same hidden line technique) in other photos and referenced.

Watch the YouTube video for an overview of using points and lines as guidelines: