Photogrammetry is a 3D coordinate measuring technique that employs the use of multiple photos which are triangulated. Working in the same fashion as your eyes do to perceive depth, using multiple photos in photogrammetry will derive similar information. A mathematical intersection between two photos can be used to determine 3D measurements.
Photogrammetry uses principals learnt in basic physics, relating to the focal length of a lens, field of view, and distance to an object; as well as principals learnt in surveying such as triangulation. That's not to say the actual calculations involved are basic..
When it comes to photogrammetry (for typical mining use) - it can be setup in different configurations; the most desirable are:
- Coordinated targets (bright, reflective targets are best) - with overlapping photos (each pair showing at least one common target)
- Coordinated stations (e.g. GPS points taken at same setup as camera) and coordinated target(s)
- Stereo camera rig (i.e. two cameras in relative fixed position) - this is more useful for very short distances
Photogrammetry can also be performed from aerial photographs (and often is the case for stockpile surveying) - see the Stockpile Monitoring section. Some mines have started using remote controlled unmanned aerial vehicles to do photogrammetry from aerial photographs; an article in the Stockpile Monitoring section also discusses this.
For the purpose of this article, we will not go into too much detail about how photogrammetry works - however if you are interested in learning more; we recommend this article: The Basics of Photogrammetry by Geodetic Services Inc.
Uses in Mining
In mining, photogrammetry can be used for stockpile monitoring, highwall surveying (derived data is normally used by geologists and geotechnical engineers) as well as backup surveys for blasts and spoil discharge. Aerial photogrammetry also has the possibility to be implemented into GIS systems for visualisation, modelling and analysis purposes.
The equipment used in photogrammetry (for the above examples at least), makes use of calibrated DSLR cameras using a fixed focal length lens as well as relevent surveying equipment for positioning targets or cameras. The positions of the cameras don't need to be known if the photo pairs capture targets at known coordinates. However by positioning the camera positions, it is possible to derive 3D measurements by telling the software where common points lie in the photos (as opposed to using targets).
For aerial photogrammetry using UAV's (Unmanned Aerial Vehicles): UAV's, GPS and DSLR cameras as well as people trained to use them would be required. To find out more about using UAV's in visit Adam Technology (3DM Analyst).
This Case Study about the use of photogrammetry in BMA Goonyella Riverside provides some further interesting information about the use of the technology in mining.
The following is an example of how photos have been used to create a 3D view of a pit by using UAV's. For more information visit Adam Technology (3DM Analyst).
The following are some examples of how photos have been used to create 3D views of highwall sections. This data can be used by geologists and geotechnical engineers to determine information about highwalls such as stability information, joints, planes and patterns.