TABLE OF CONTENTS If an image has been calibrated using the method described in Chapter 15, any object on the same plane as the ruler can also be measured. The two key issues are that the calibration must be done with precision and the object must be on the same plane as the ruler.
When an image has been calibrated, the diameter and distance between bullet holes in a wall, the size of a knife blade, or the distance between features in a tool mark or tire impression may be measured.
In addition to measurements of length, angles can be measured.
Annotations of these measurements can be made in a separate layer and used for later calculations or as part of a court display.
| Note | In macro photography, if an object is only a centimeter closer to the lens than the ruler, measurements can be significantly off. That same centimeter difference in distance may not show a measurable difference in general scene photography. The rule of thumb is that the closer the objects are to the camera, the more critical it is that the ruler and subject are on the same plane. |
In Figure 16.1, there are annotations to show the distance between two points on the star, the diameter of the hole in the center of the star, and the angle of one point. The steps to make the measurements and annotations areas follows:
Calibrate the image view using the techniques in Chapter 15.
Create a new layer...
