There are some additional requirements when taking photographs when you know you will be modeling with curves, edges and/or cylinders. See section below for more detail on curves.
PhotoModeler's edge, curve and cylinder algorithms depend on a good angular separation between the photos as rotated about the object centerline. The angle ideally should be 90 degrees but you will get good results down to as low as 15 degrees. Where we refer to "cylinder" below you can replace "edge" or "curve section" and the meaning is the same.
The following diagram shows the end-on view of a cylinder and the two camera positions for two photos being use to reference it. This example would give a good cylinder result.
This next example would give a worse result because the possibility for error in the cylinder or edge algorithm is greater.
Another way of thinking of the requirement is this:
• if you have vertical edges or cylinders then you need photographs that move along the horizontal direction
• if you have horizontal edges or cylinders then you need photographs that move along in the vertical (height) direction.
Using cylinders as an example again we show an example in the figure below. If you were to use just photographs A and B you would get good results for the horizontal pipes because of the good angle separation about the horizontal pipe centerline. On the other hand A and B would be bad photographs for the vertical pipes because there is very little angle about the vertical pipe center line.
Photographs C and D are good photographs for marking the vertical pipes but are poor for the horizontal pipes.
This means that to model both sets of pipes you would either need all four photographs in the project or you could use a two photo combination like A and D but that would not be ideal.
You can think of Edges and thin pipes/cylinders and small segments of curves as thin short sections of pipe/cylinder. In this way this example encompasses all object types.
photography for horizontal and vertical pipes