Aerials Express, LLCSales Representative7855 River Parkway, Suite 211Tempe, AZ 85284Telephone: 480-777-9909Fax: 480-777-9966Email spetersen@AerialsExpress.com
Much is determined in the first step of scanning. It is important that this step is done correctly in order for the remaining steps to run smoothly. It is for this reason that a ZEISS Photo Scan photogrammetric scanner is used to perform all scanning in-house. This provides complete control for both resolution and color balance at the start of the process.
Automatic Triangulation and Rectification We use Intergraph's Image Station Auto-Triangulaton (ISAT) system that works hand-in-hand with IMU/ABGPS data to match photos together. It is an automated process to create automatic tie points between photos. The process uses a bundle adjustment to tighten the accuracy of the tie points. Upon good AT results, we then use a DEM to rectify the photos with Intergraph's Image Station Ortho Pro (ISOP) software. Color Balancing and Seamline Generation
After rectification an overall tone balancing using ER MAPPER Software is applied to the aerial photo project. Seamlines or a stitching process are then assigned between each image to ensure a more seamless mosaic. The mosaic is then tiled into tiff images.
Aerials Express takes great care in the tone and color balance of the imagery. The ER Mapper software provides the automatic color correction of the imagery in batch mode. As a final review, Adobe Photoshop is used to correct color and image density where stitching is not able to fully disguise the match lines. The final step in this process is to color balance the entire image file to the best color, which gives the photography a completely natural look.
Production Process for ADS40 LEICA DIGITAL IMAGERY
Data processing of ADS40 imagery and metadata is a streamlined digital workflow process utilizing commercial softcopy photogrammetric software including Applanix POSPAC, Leica GPro, ORIMA, SOCET SET and Orthovista.
The ADS40 sensor GPS/IMU position and attitude data is directly processed through three separate but continuous steps: Applanix POSPAC for data extracting, POSGPS for data orientation, and POSProc for creating a Smoothed Best Estimate of Trajectory (SBET) for each flight lift. The post-processed GPS data output is displayed onto the flight profile plot, which clearly shows the RMS values of the combined forward and reverse run separations, C/A Code and Carrier Phase. The output IMU data is also verified by a PDOP plot and its value compared to an acceptable threshold range.
The processing of ADS40 images is run on Leica GPRO and ORIMA for bundle adjustment. The image is linked to the local coordinate system through the corresponding GPS/IMU SBET data with correct position and orientation. The residual of the tie-points are displayed instantly to reflect the accuracy of the processed data. After the bundle adjustment, ORIMA automatically displays the unit weight standard deviation, the RMS of tie points and the accuracy of the sensor position and orientation. The iteration process on the bundle adjustment is based on the selected parameters to ensure the data integrity and accuracy is within the project specification. The software also provides the measurement of reliability for variance and co-variance component analysis. This ensures the processed data is statistically satisfied on the application demand.
The triangulation process involves automatic measurement of tie points. All operations are performed using the graphical working environment of ORIMA. For automatic tie point measurement, the Auto Point Measurement (APM) from Orima, using a very dense point measuring algorithm adapted for the ADS40, is called directly. Highest quality orientation results are obtained by a combined bundle adjustment. The Combined Adjustment Program CAP-A has been extended to handle all types of observations required for ADS40. The observations are image coordinates, and position and attitude values from GPS and IMU computed by the IMU/GPS post-processing software. The post-processing includes the transformation of the raw data into the reference image frame used for the aerial triangulation. The resultant values of this transformation are the same as orientation elements of standard photogrammetry procedures and results.
"The use of the high precision GPS/IMU data combined with these traditional triangulation techniques gives rise to a very robust and flexible system. The adjustment process can determine calibration, datum deficiencies, errors in GPS and more precisely register the imagery to ground control. It should be noted that very little ground control is required. Owing to the GPS/IMU data, ground control is essentially unnecessary." Hinsken, et al, Program author of Orima.
Raw imagery is checked and radiometric balanced in a parallel process that utilizes custom gradient correction software and the Leica GPRO Tonal Transfer Curve (TTC) application. While operators are refining a good AT result, others are carefully reviewing the imagery for good color band balance, contrast and tone.
Once both processes have passed rigid AT and QC milestones, the imagery bands, red, green and blue or NIR, red, and green are rectified to an RGB or CIR product. These orthos are passed to the mosaic team for QC, seam line placement and tiling using the vigorous interactive capabilities of Orthovista software.
For this project, the latest available National Elevation Dataset NED surface model is used for rectification."