Process_Description:
Data processing of ADS40 imagery and metadata is a streamlined digital workflow process utilizing Xedar, Inc.'s proprietary software and commercial softcopy photogrammetric software including Applanix, GPro, ORIMA, Pictovera, 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 analysis and POSProc for data measurement. The post-processed GPS data output is displayed onto the flight profile plot, which clearly shows the RMS values of the combined separation, C/A Code and Carrier Phase. The output GPS/IMU data is also verified by a PDOP plot and PDOP values are compared to an acceptable threshold range.
The processing on ADS40 images is based on Pictovera software for bundle adjustment. Image tie points providing the observations for the least squares bundle adjustment were selected from the images using an autocorrelation algorithm. A least squares bundle adjustment of image pass points and the ABGPS was performed to develop an aerotriangulation solution for each block using Pictovera software. Upon final bundle adjustment, the triangulated strips were ortho-rectified to the DEM. XeDAR generated an elevation model through auto-correlation processes. Upon completion of the Aero-Triangulation (AT), PictoVera software was used to automatically correlate a dense elevation network of x, y, z (3D) points from the stereo-viewable imagery from each flight line. With a general density of approximately one point per every 1 -2 meters, the 3-D points were reviewed and manually edited for gross errors. Additional filtering was performed to remove points that were found to have been extracted from the surfaces of elevated buildings and trees, using SimActive DEM filtering software. Upon final filtering, the resulting DEM was suitable for the accurate rectification of the aerial imagery.
Orthorectified imagery is checked and radiometricly balanced in a parallel process that utilizes custom gradient correction software and the INPHO Orthovista Radiometrics editor. Once both processes have passed rigid AT and QC milestones, the imagery bands, red, green, and blue, are rectified to a 3-Band RGB product. These orthos are passed to the mosaic team for QC, seam line placement and tiling using the interactive capabilities of Orthovista software. Following the application of seamline and final tonal adjustment, the orthoimagery is cut to a custom tiling index. The orthorectifed imagery was originally produced in UTM 17N NAD83 Meters and as a final step was reprojected to Geographic NAD83 Decimal Degrees