Technical Area
PHOTOGRAMMETRY
Our softwares use a technology called "Photogrammetry". Photogrammetry is a relatively ancient science whose principals were defined by a Frenchman : The Colonel A. Laussedat (1819-1904) in 1854.
Photogrammetry uses the triangulation principle and allows relief to be defined from two flat images of an object taken from two different positions. It's what our brain does all the time in conjunction with our eyes' retinas.
The principle is rather similar to that of the well-known GPS (Global Positioning System) which allows you to determine your position anywhere in the world to within a few meters.
The main difference (and difficulty) between our software and GPS is that our software doesn't know the 3D position of the cameras when the pictures are taken (whereas the exact position of the satellites is known with GPS ). This position must be calculated based on points on the photos (the centers of targets) before being able to create 3D points.
Our Softwares uses the most recently developped technology and mathematical algorithms.
CAMERA CALIBRATION
Camera calibration is "the" essential phase in order to obtain precise digitizing.
Calibration is only performed once for each camera. If you have several cameras or several lens you must carry out the calibration procedure for each camera/lens.
Geometric lens and mechanical assembly tolerances result in the fact that the real "focal length" of the camera is not exactly the same as the focal length indicated by the manufacturer.
The "Principal Point" of the CDD sensor is not systematically in the center of the sensor. Determining the real position of this "Principal Point" is essential in order to calculate the exact 3D positions of the camera.
It is necessary to precisely determine the "Lens Distortion" in order that the software can compensate for this error.
It is essential to "calibrate" your camera.
You should be aware that the procedure only takes about 5 minutes, is fully automated and only has to be performed once for each camera that you have.
Some usefull links
http://en.wikipedia.org/wiki/Epipolar_geometry
http://en.wikipedia.org/wiki/Photogrammetry