Aerial Triangulation

RSGS performs Digital aerial triangulation utilizing state-of-the art software to provide a highly accurate analytical solution.

Softcopy aerial triangulation:

  • It is an entirely digital process using scanned images of film negatives or scans from DMC
  • It is more advanced, accurate and economical than traditional aerial triangulation
  • Produces a highly precise solution on all sizes of projects

How it works :

In the softcopy approach to aerial triangulation, the first function is to set up the project parameters, including camera calibration files, project coordinates and digital image file locations.

All eight image fiducials are measured. Interior orientation is performed automatically, and any fiducial measurements or orientations that exceed a defined limit are flagged. This process defines the mathematical relationship between the digital image pixel coordinate system and the calibrated camera coordinate system.

Image correlation technology is used to perform tie point measurements and generate numerous passpoints for each stereo model. The operator can then interactively measure additional points to obtain an appropriate density and to measure both ground control locations and exposure-to-exposure, flightline-to-flightline passpoint locations. A preliminary aerial triangulation adjustment is run on the measurement data to locate and flag points with residuals that exceed project parameters. A senior technician evaluates the measured points and analyzes the preliminary results. Each point is assigned a weighting factor based on its reliability and importance to the final solution, with Ground Control given the highest weighting and passpoints a lower value.

Once the residual values have been accepted, a final triangulation adjustment is performed. The software applies corrections for systematic errors such as earth curvature, map projection, film deformation, lens distortion and atmospheric refraction, using geodetic transformations, camera calibration data, and flight altitudes and mean ground elevation.

Ground control points are withheld from the initial computer runs to verify results of the aerial triangulation computations. Once the results are verified, these points are included in the control file and processed in the final aerial triangulation adjustment.

The accuracy of the digital  aerial triangulation will be less than 1/15,000th of the flight altitude as determined by the root-mean-square (RMS) error of the horizontal ground control pint residuals, and less than 1/10000th of the vertical control point residuals.

The final result is a set of adjusted coordinates in terms of ground coordinate system and exterior orientations (EO) for the entire project, including a set of orientations for each frame. This data will be used to orient the stereo models for data collection and orthophoto generation.