Below is the next and last section of the paper “Benefits of UltraMap for Keystone Aerial Surveys” from David Day, Director of IT for Keystone Aerial Surveys Inc. This section focuses on UltraMap radiometry advances, UltraMap AT, and finally David shares conclusions. If you missed previous installments of this paper, you can find the last here. Thanks to David and Keystone for sharing this paper that I hope you all have found value in reading.
– Jerry Skaw, Sales and Marketing, Microsoft UltraCam Team
UltraMap Radiometry Advances
UltraMap Radiometry Advances The large blocks also were used to highlight the other main feature of UltraMap – Project Based Color Balancing (PBCB). Again, the radiometric tools are designed to work in conjunction with the new COS and do not have as rich a feature set with imagery taken with the old COS. The ability to add environmental conditions and to use the location, orientation and time of the exposure to provide tools that remove hotspots and sun glare will be essential in Keystone’s ability to complete large orthophoto projects. Below are sets of images from the block of the 2577 images in Northern Minnesota, one processed with OPC and the other UltraMap. This was a small part of a larger Ortho project that Keystone performed recently. The imagery from OPC had strong sun glare that was unable to be removed with OPC’s tools and was only partially handled by Ortho Vista’s automatic tools. Much individual balancing of orthos and ortho tiles was done in both Photoshop and Ortho Vista’s Radiometrix. The UltraMap imagery has almost all of these radiometry issues removed and requires only flight and/or block wide adjustment of the imagery or ortho tiles before delivery – the labor savings is substantial. Note that the full capabilities of the PBCB could not be used because of the older COS, so new imagery shot under similar conditions should produce even better end results. The two images below show a much larger area and the improved tonal balancing between flight lines. The first is using OPC and the later using UltraMap.
When using UltraMap AT, the user can create a Project Based Color Balance DragonFly project that will use the immense redundancy in the tie point collection to link imagery together radiometrically. This allows the block to work as one when making radiometric adjustments.
The use of Project Based Color Balancing means that each project will have a tie point collection run whether there is a need to do a bundle adjustment for additional products or not. This is an excellent reason to use UltraMap AT as Keystone’s tie point collection and initial bundle adjustment utility. To that end, Keystone recorded the times for each block run for the tie point collection testing. The blocks were run on a Windows Vista 64-bit machine with 16gb of RAM and 2.83ghz CPU 8 cores while the UltraMap node used 5 Windows 2008 64bit servers each with 6 cores available. The impressive results are below.
Not only is the UltraMap tie point collection faster, but more quality points were obtained with higher redundancy. The speed is due to the use of distributed processing and the use of DragonFly technology and is unlikely to be bested by other distributed systems or GPU processing because of IO difficulties with accessing ordinary tiff files. The added time in initial processing becomes worth it when the time savings in AT are taken into account.
- Determine if the bundle block adjustment generated from UltraMap-AT is comparable to Match-AT.
- Create DEMs for each of the blocks to determine if the greater spread of tie points translates to a more accurate surface model.
Conclusions The introduction of UltraMap as the center piece of Keystone’s workflow created an additional expense of adding state of the art hardware, but the ability to capture imagery over water and unstructured terrain, greater vertical accuracy, the homogenous spread of tie points and the advancements in radiometry make the choice simple. The new features and advancements within UltraMap lead to a better final product. Even though accuracy levels show only small amounts of improvement, when many of Keystone’s clients are looking for very high accuracy at very small GSDs, every bit will help. The ability to create well balanced radiometry projects in an automated manner coupled with the high speed of the automated tie point extraction makes UltraMap a logical choice. If the bundle adjustment ability of the software is acceptable (as it is certain to be) then UltraMap is definitely a strong choice for an all around solution. The addition of PCI Geomatics as a partner brings the rapid production of orthophotos into the workflow, however automated or semi automated DEM production is not available and is the only part of the chain missing when looking to UltraMap/PCI Geomatics for a complete ortho production workflow.
– David Day, Director of IT, Keystone Aerial Surveys