Define Geometry 
The Define
Geometry Tool allows you to make new geometry based on existing
geometries. To use this tool, you must have geometries defined on
your image. (Use the Fit Geometry Tool for this.)
Select the Define Geometry Tool then select (click on) two
existing geometries on your image - a line will be generated between
them.

Right-click
on the line to bring up the LineSegmentEntity edit box, as
seen below. Selecting
the Entity tab allows you to adjust the colors, thickness, size, type and
visibility of the line. You can also select a
Coordinate System. Make the necessary adjustments, click
Apply and then Close. The values will be updated according to
your selections.

Selecting the Line
tab allows you to enter values for both X, Y, and Z coordinates.
Make the necessary adjustments and click Close. The line
segment will be updated according to the values selected.
