What is photogrammetry?
The Basics of Photogrammetry
Photography - The First Part of Photogrammetry
The three main considerations for good photography are:
Field of View
The diagram represents a pyramid with the four factors at the base of the pyramid and high accuracy at the top of the pyramid. To get higher accuracy ( a higher pyramid) you need more of the items shown on the lines of the pyramid (higher resolution, smaller size, more photos, and wider, but not too wide, geometry).
Photo of a car, you dont know whether it is a real car or a toy car
If the image has a person in it, you derive the scale from the person's height, and then infer that is is a real car!
Multiple Scale Distances
Long Scale Distances
Planning the Measurement
Questions You Should Ask: Remember "V-STARS"
Defining a Coordinate System
Types of Measurements
Initial and Repeat Measurements
Completely or Partially Overlapping Measurements
The common line only acts like a hinge, the two panels are connected there but they could be at any angle to each other that this "hinge" connection allows. Therefore, the overlap must be more than just a line of points; it must be at least two-dimensional.
If we now add a third point in common between the two measurements that is away from the line (so the three points form a triangle), the "hinge" is now locked in place and the relationship between the two panels is established. Therefore, as a minimum, there must be three points, forming a triangle that is seen in common between the two sets of photography.
Planning for Different Types of Measurements
Design for Completely Overlapping Measurements
Conversely, if the object were convex (for example, the back surface of the antenna), the camera intersection angles would have to be smaller so the retro-reflective targets at the edges could be imaged. In fact, depending on the curvature of the surface, the camera intersection angles may have to be so severely compromised, that it would be better to design the measurement so the object is measured with partial overlap.
In addition, your plan must consider blockage. Remember, we want to try to see ALL targets from at least four different locations. If part of the object cannot be seen (for example, the antenna feed may block part of the surface), try to take extra pictures from other locations that see the blocked targets. However, it can often be difficult to get good geometry if the blockage is severe. (A good example of this is trying to measure targets at the bottom of a long, thin cylinder.) If blockage or other limitations limit the number of favorable views we can get of the object or a portion of the object, we can improve accuracy somewhat (10-20% typically) by taking another photograph from the same location. You can improve accuracy further (another 10-20% typically) by taking the photographs with the camera rolled at a different angle for each picture.
Design for Partially Overlapping Measurements
Design for "Left-Right" Measurements
Design for "Front-Back" Measurements
Design for "Box" Measurements
Procedures for Different Types of Measurements
Final Planning Tips
Planning Summary and Checklist
Retro-reflector Targets and Their Characteristics
For best results, always use the same or similar size targets on a given measurement. Target sizes which vary by up to 2 to 1 in size, generally are acceptable.
Dots in tape roll
Hard Body Targets