Semi-Global Matching (SGM)
Information Cloud Photogrammetry
Photogrammetry’s newest methodology or tool in the toolbox is the high resolution Information Cloud. Any given point in a final data set in traditional photogrammetry or LiDAR has an XYZ coordinate. Now with the advent of the “Information Cloud” any given point could have an XYZ, time stamp, R, G, B, NIR as well as NDVI values. This is made possible by “SGM” or semi-global-matching.
Semi-Global Matching (SGM) is the latest technology developed to further enhance the advantages of the Zeiss/Intergraph DMC-II-140 aerial mapping system. Utilizing aerotriangulated digital frame imagery, a high density surface model is generated for use in orthophoto and map production. Capturing imagery and surface models during the same flight with the same sensor ensures that image features and image geometry perfectly match with the Digital Surface Model (DSM). The resulting pixel level correlation generated point cloud is photogrammetrically accurate to the same level as the mapping. The point density achieved (300 points/m2 at a 5cm GSD) is far greater than airborne LiDAR (8 to 10 points/m2 for 1-foot contour accuracy) derived point clouds for the same accuracy level yet the image based point cloud (DMCII – 140 at 3cm GSD, fixed-wing aircraft) accuracy approaches accuracy levels achieved by a mobile based LiDAR collect in open areas on hard surfaces. This process minimizes the need for additional LiDAR flights in the use of the production of orthophotos and various other products.
The primary advantage of the Information Cloud is one flight – multiple products. Utilizing the image acquisition capabilities of Midwest Aerial, our geospatial clients can deliver photogrammetrically derived engineering design scale mapping, DSM, orthophotos, hydrology models, compute volumes, produce vegetation studies based on the NDVI and more all from a single DMCII -140 acquisition flight and depending on the GSD, this data can all be accurate to the level of engineering design scale mapping. The DMCII-140 has a single PAN CCD (144 MP, 92 mm focal length, 7.2 micron pixel size) which has a footprint of 12096 X 11200 pixels. This large footprint allows for less exposures and less flight lines when compared to a DMCI sensor and other large and medium format cameras which leads to a more efficient and cost effective acquisition solution. In addition to the single PAN CCD, the DMCII also has 4 multispectral CCDs (RGB & NIR) each with a resolution of 42MP and a focal length of 45mm. The PAN to color ratio is 1:2 which provides a high-radiometric quality and detail for RGB and CIR. On any given flight, Midwest operates all CCDs and therefore collects 4-BAND imagery with every flight. It is in the post processing phase, depending on the client’s needs, where the final image deliverables and ABGPS/IMU data are finalized.
One flight acquisition/mobilization represents a tremendous cost savings not only in acquisition fees but production costs as well. Contact Midwest Aerial Photography to discuss the latest innovations in Photogrammetry and Image acquisition and allow us to provide the most cost effective solution for your next project.