Can I use photos that aren’t from my own camera?

Yes, you can.

There are a number of ways to work with photos from cameras where you do not have access to the camera. For the most accurate results it is best to use photos from a calibrated camera. If you have photos from a camera that has not yet been calibrated, PhotoModeler has some functions to perform that calibration.

1. Using Auto-Calibration: If you have multiple photos from the same camera, taken at different angles and the subject material either has Coded Targets or has a natural texture, then an automated project can be run (either Coded Targets or SmartMatch) and during this processing, you can request the camera also be calibrated from the same data. There will need to be enough photos (usually 8 or  more) and from good angles. It will help if the photos have EXIF data to get the process started well.

2. Using Control Points: You can use control points to solve the camera when processing if you have known 3D positions of several points in the photo(s), or you have several known dimensions and are able to calculate the 3D positions of several points in the photo relative to each other. You can obtain control points from a LIDAR point cloud, from a survey or by doing a regular PhotoModeler project of an ‘exemplar’ object and then importing the model as control points.  This method is good when you have just a single photo (auto-calibration cannot be used) but do have access to externally known data.

You need a minimum of four (4) control points (more is better) covering a substantial part of the photo. Once a control project is processed and the camera is solved, you can extend surfaces and mark features on surfaces using surface draw. You can then also turn off the Inverse Camera flags on the photos (so that the camera solution stays constant) and proceed with marking and referencing points across photos, as you would with a regular PhotoModeler project. Since you are using known coordinates, your scale will be implicitly defined.

3. Using Constraints: Again best suited to single photo projects and if you don’t have access to known control XYZ data. If your photo(s) have strong 3-Point perspective with horizontal (left-right and front-back) and vertical features that you can mark, you can use ‘axes constraints’ to constrain marked features. Once the camera is solved, you can then mark surfaces to connect the constrained items, and then use the Surface Draw tool to mark and measure features on the surfaces. Measurement in PhotoModeler requires that you set a scale by using one known dimension in the photo. This could be set using a standard feature dimension such as a manhole cover diameter or the wheel base of a known vehicle, etc.

When working with single images and photographs you can refer to Solving Single Photo Geometry with External Data for details and reference material.