GPS base station

Differential corrections of recorded airborne GPS signals are possible if a base station has been established in the vicinity of the project area. Usually we set up an ITRF point which provides sub-centimetre accuracy on the base station.

 

Typical post-processing results of the camera projection centre position in space are of the decimetre order, well sufficient for assisted aerial triangulation

 

 

Download of flight data and image processing

The airborne GPS and IMU data is downloaded and forwarded for post-processing. The raw imagery is downloaded from the storage unit and can be converted to the appropriate level.

 

The UltraCam system operates with the following data levels: Level-00: Raw data, each triggered images consists of 13 sub-images, stored twice.

 

Level-0: Verified data, same as level-00, but no duplicate copy exists.

 

 Level-1: Internal intermediate format, maintained as 13 sub-images, but radiometrically corrected using calibration files.

 

Level-2: Deliverable format, per image only one single frame, the sub-images are stitched and geometrically corrected using the calibration files. The panchromatic data are in one file, separate from the four colour files. Colour remains at its input resolution, but is geometrically matched to the panchromatic image. Data are at 16 bits per channel (5 channels).

 

 Level-3: Pan-sharpened colour images in R-G-B, in CIR or in R-G-B-NIR. Format in 8 or 16 bits, at the discretion of the user.

 

Differential GPS and IMU post-processing

 

Before the aerial triangulation process can take place, the trajectory is computed via Novatel’s GrafNav software. A quick assessment of the quality of the measurements can be done.

 

This step is essential in the determination of the position of the camera projection centre for each captured image.