Aerial Triangulation represents the mathematical process of establishing precise and accurate relationships between the individual image coordinate systems and a defined datum and projection (ground).
The main objective of aerial triangulation is to produce from ground control, sufficient points in the photogrammetric models to ensure that each model can be oriented accurately as required for stereo compilation, in either DTM generation and enhancement ( for orthophoto production) or 3D feature extraction.
The Aerial Triangulation process can be accomplished easily for all kind of aerial sensors (both analog and digital) and also for satellite imagery. Using GPS/INS accurate data, the the number of GCPs during the Survey Missions can be considerably reduced by using the latest state of the art software and this technic is known as Integrated Sensor Orientation ( that involve a data bundle adjustement for an aerial triangulation block).
For each block, the flight is done taking into account the terrain elevation and roughness (for obtaining the correct GSD) and the GCPs repartition is done ( as possible), by considering a balanced distribution across the block. The cross flight strips are a plus and can strengthen the accuracy of the final bundle adjustement.
The Check GCPs are a must and their number should be around 20% to 50% , from the total number of GCPs.
The quality control of aerial triangulation is done by assuring the working steps completeness and the final results consistency :
- the relative orientation is satisfactory for all images in a block
- the residuals of AT compensation are smaller than 1.2 * pixel image size
- RMS values are les than 0.8 * pixel image size
- the Sigma0 value (assessment index) is situated in the interval of 1/3 and 3/4 * pixel image size
- RMSxy and RMSz for GCPs (also check GCPs) are smaller than the final GSD of the block
Aerial triangulation process