Aerial Mapping Fall '13 - Aerial Mapping Fall '13
North West Geomatics Collaborates with Leica Geosystems to Automate Image Processing Workflow
By Kevin P. Corbley
As an aerial mapping contractor, North West Geomatics is under pressure to collect aerial imagery, process it, and deliver orthorectified products on tight deadlines. When the Calgary, Alberta, firm bought its first Leica ADS40 digital sensor a decade ago, it saw an opportunity to create an automated digital workflow. Leica Geosystems was happy to support the effort. The result of this collaboration is the commercially available Leica XPro package.
Compared with frame-based aerial cameras, North West saw advantages in automating the processing of data collected by the pushbroom scanning design in the Leica ADS40. Instead of individually processing thousands of scenes captured by a frame camera, the pushbroom scanner collects hundreds of kilometers in long pixel carpets – just a handful for each project. A newly developed workflow would have to leverage the advantages of the long image strips collected by the ADS series, and Leica was eager to lend its support to North West.
North West focused on engineering the new processing approach based on the idea that any step performed by humans that could be automated would be – even if the computer took many times longer. This was considered a viable trade-off because computers were increasing in speed rapidly, and clustering machines to split long running number crunching tasks among multiple computers was rapidly becoming mainstream.
“Instead of trying to make human processes more efficient as our first goal, we moved as many of these processes as possible to compute tasks so all the technician has to do is monitor the machines, and approve the results,” said John Welter, Vice President of Technology at North West Geomatics. “We purposely turned our problem into a high-performance-computing (HPC) problem as we knew HPC had lots of smart people working to solve these issues and we could leverage that work.”
In a typical project, the North West crew initiates the XPro workflow from the airfield. After a flight, the crew immediately ships to Calgary the solid-state drive containing both the ADS image data and the IPAS GPS/IMU position data. The crew logs onto an internal website to let XPro know the data is coming and what project area it covers.
When the data arrives, one of North West’s production technicians plugs it into the computer. XPro acknowledges the expected data sets have been received and separates the image data from the GPS/IMU data. The raw image data is converted to a format for further processing. During this step, the image data is organized into pyramids so technicians can zoom in and out to look at the data in detail, if needed. The GPS/IMU data, which correlates precise location and aircraft attitude information to the image stream, undergoes a separate automated quality check.
In the processing, XPro runs Automatic Point Measurement (APM) on the image data, which is then sent into a queue until a large production block has been amassed. If flights are proceeding quickly, North West may gather five to 20 long image strips because it’s more efficient to process many flight lines with a handful of control points at once. This is where the workflow leverages the advantage of the long continuous line of pushbroom data.
Once the massive block’s APM is complete, XPro begins aerotriangulation on the entire data set using an application called ORIMA, also sold by Leica Geosystems as a stand-alone AT software product. After each adjustment run, an automated process runs analyzing results looking for areas that do not meet accuracy requirements. If the triangulation results fail in an area, APM is used to add additional points in that area and the aerotriangulation is processed again to see if it now meets the accuracy requirements. The number of points needed for a block adjustment is usually quite small for the ADS imagery.
Once the aerotriangulation is completed, an AT technician launches the orthorectification process, which works on the entire block in the same cluster of computers. North West uses open source software called Condor to manage the processing in the cluster. While Condor is standardized for XPro, a technician can prioritize a particular phase such as ingest, AT or orthorectification to use more compute power to speed completion.
For orthorectification projects performed in parts of the world where digital surface models are unavailable or unreliable, there is an optional XPro module available called Semi-Global Matching (SGM). This computationally intensive algorithm generates 3D elevation surfaces directly from the image data.
As processing continues, another process performs quality control analysis on the orthorectified data by measuring common points between image strips and control points to ensure they meet accuracy specifications.
Finally, XPro uses automated techniques to perform several finishing steps including seam line computation and color balancing. After a final visual inspection, the system generates the end products. Total processing time for the XPro workflow is typically compared to flight time. For every hour of flight time, ingest takes one hour, AT typically lasts two hours, and orthorectification with finishing consumes 0.5 hours. The optional SGM process uses 10 hours of compute time.
The concept of creating an integrated workflow in which multiple phases of image processing are occurring simultaneously and in parallel with clustered computers has successfully reduced the time needed to generate orthoimagery from the ADS series of cameras.
“Operators of other Leica airborne sensors can expect the XPro workflow approach to be extended to their products in the future,” said Ruedi Wagner, VP Business Unit Solutions for Leica Geosystems.
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Hexagon Geosystems’ newly formed Geospatial Solutions Division is bringing together Airborne Sensor solutions from Leica Geosystems and Z/I Imaging. With over 80 years experience, Leica Geosystems is a global leader in the design, delivery, and support of airborne digital and lidar sensors for the geospatial marketplace. Along with the well-known Leica RC30, Leica Geosystems’ airborne sensor portfolio today includes a wide range of innovative technologies and products such as the Leica RCD30 series of medium-format digital frame cameras, the Leica ADS pushbroom sensors, the Leica ALS Lidar series, and the Leica IPAS GNSS/IMU solutions. For nearly the same 80 years, Zeiss and later Z/I Imaging have set standards in the airborne photogrammetric market with such products as the RMK series and the DMC. Today, Z/I Imaging continues to drive innovation and productivity with the new DMC II range of digital mapping cameras. Sensors from Leica Geosystems and Z/I Imaging are fully integrated in a suite of end-to-end workflow solutions. These include flight planning, GNSS/IMU processing, as well as the most comprehensive post-processing tools for the delivery of map products and 3D models in the fastest time possible. Hexagon Geosystems’ combined airborne sensor portfolio of Leica Geosystems and Z/I sensors offers complete solutions for almost all airborne mapping applications, plus all business models, and continues to give each sensor owner the highest and most consistent return on investment. In addition to world-class sensors, Hexagon Geosystems offers a full range of product support, service, and training with offices located in over 25 countries worldwide.
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