The Department of Surveying is ensuring latest 3D datasets for its city planners
With the aim of having the most up-to-date geospatial data available for city planners, the City of Graz (Austria) Department of Surveying is on a mission to acquire complete aerial data of its city. To accomplish the mission, the Department partnered with Austria-based Terra Messflug GmbH and its parent company Vermessung AVT ZT GmbH. Terra Messflug provided the data acquisition while AVT provided the postprocessing of the imagery and produced the end products in a development project with the new software version at Vexcel Imaging: digital surface models (DSM) and DSM based orthophotos. A commonality among the cooperating organisations: Microsoft photogrammetric technologies.
Stage one of the project began on June 22, 2011. In a Cessna 303 equipped with a Microsoft Ultra- CamXp and flying at roughly 1000 metres above ground to capture 6 cm views, Terra Messflug collected 4034 images at average 80% forward overlap and 60% sidelap. In the next stage, the raw UltraCam imagery was provided by Terra Messflug to AVT for ingest in its Microsoft UltraMap photogrammetric workflow system for post-processing. During this step of processing, the UltraMap aerotriangulation module automatically collected tie-points from the overlapping imagery. In a semi-automatic process, the AT module allowed AVT to generate refined exterior orientations, import ground control points and GPS/IMU data. These data were then handed off to Vexcel Imaging for further processing to final products using the prototype of its latest version of the software, UltraMap 3.0.
UltaMap 3.0 features new modules for generating high-density point clouds (to the order of 300 points per sq. metre), digital surface models and orthophotos. From the UltraMap processed imagefiles from AVT, Microsoft used the new UltraMap 3.0 software to read the aerotriangulated results along with the parameters of the radiometric adjustment and automatically executed the dense matching process that generates the heightfield and renders the DSMOrtho (an accurate orthophoto derived from a digital surface model). From there, Microsoft exported the resulting datasets-the digital surface model and the DSMOrtho in RGB and CIR. With the help of an in-depth quality analysis by AVT, further improvements to the software prototype were achieved and Microsoft delivered the refined results to the city of Graz where the data will be used for various applications. Besides the output for this project, the software UltraMap is able to process a DTM-based ortho (with automatic filtering of the DSM to the DTM) and a 3D point cloud. That point cloud is a real 3D dataset, because it even involves successfully matched points on façades and other vertical features.