Aerial triangulation in 3D aerial photogrammetry

Aerial triangulation in 3D aerial photogrammetry is a mathematical process used to determine the position and orientation of each photograph at the moment of exposure. Aerial triangulation in 3D aerial photogrammetry solves for each photo’s exterior orientation parameters, which convey the information necessary to convert image measurements into ground coordinates, as well as determine image points that correspond to points on the ground.

- Aerial triangulation in 3D aerial photogrammetry is a critical step related to the project’s quality, and is at the heart of all photogrammetric processes.

- The computed result of Aerial Triangulation in 3D aerial photogrammetry gives the computed EO parameters (X, Y, Z, omega, phi, kappa) which is used to generate the highly accurate stereo model (3D) without any parallax which is further used for DTM generation, Orthophoto creation, Mapping purposes, Application of different projects like urban planning, Utility mapping etc. 

- Aerial Triangulation in photogrammetry is the first step to perform in the Photogrammetric Project. 

- Aerial triangulation has been a complex operation which includes planning the photo flight, establishing ground control points, taking and developing aerial photographs based on preset specifications, performing interior orientation, measuring and transferring all tie, check, and control points appearing on all photographs, and performing a least squares block adjustment.

- This process ultimately provides the exterior orientation parameters for all photographs and the three dimensional coordinates for all measured object points.

- Inner Orientation requires measurement of image coordinates of fiducial marks; this orientation is followed for the images taken with analog camera which is having fiducial marks. 

- The measurement of tie points could be done manually or automatically. 

- The automatic measurement of corresponding points for Relative Orientation is based on the image matching. 

- The measurements of control points are necessary for Absolute Orientation of photogrammetric model. 

- The knowledge about convenient choice of their position is important for good quality of the training process. 

- The automatic identification of control points is more difficult. At present there are two strategy lines in practical use, which can be pursued in digital aerial triangulation in 3D aerial photogrammetry. 

- The first strategy uses semi-automatic methods in which the human operator selects interactively one or several suitable tie-points in an image and gives the approximate location of its homologous points in the other images. Then the image point is transferred automatically by image matching.

- The second strategy, which is pursued here, goes one essential step further and attempts a fully automated procedure for selecting, transferring (matching) and measuring tie-points. 

- In this case not only the selection of tie-points is automatic but the approximations are obtained automatically too. The operator only has to give the initial approximations (block-configuration, forward- and side-overlap) and control the results. 

- The main specifications of aerial traingulation in 3D aerial photogrammetry is the system’s concept are automation and sub pixel accuracy.