October 2009 | Research and development
Stereo image matching: breakthroughs in automated change detection
By Bingcai Zhang and Mike Walter
An NGATE analysis of a WorldView-1 satellite image of Beijing’s Bird’s Nest Stadium shows a DSM as cyan contours and a DEM as red contours (inset). Both are two-meter intervals. In the middle of the stadium, the DSM and DEM have blunders due to moving objects, which makes it difficult for a human operator to place an extraction cursor on the ground. In the upper left corner, the water body also causes DSM and DEM blunders. BAE Systems’ forthcoming automatic water body extraction will address this problem (Image courtesy of DigitalGlobe).
In a good stereo pair, humans readily fuse the two images and perceive a 3-D scene. The relief may be exaggerated, but our brains are comfortable with the presentation. Similarly, stereo correlation algorithms used for automatic terrain extraction operate nicely on good stereo pairs. But localized differences between stereo image pairs can cause headaches for humans and correlation software alike. For human observers, these differences confound our natural stereoscopic vision. It is immediately apparent that something isn’t right. The differences also confuse image-matching terrain-extraction software. The results include spikes, wells and other elevation anomalies that previously required manual editing to correct. BAE Systems recently developed an algorithm to automatically detect and remove false matches caused by moving vehicles as part of Next-Generation Automatic Terrain Extraction (NGATE) enhancements for the company’s SOCET SET and SOCET GXP photogrammetry software. The algorithm also provides an automated way to detect change between image pairs, including change caused by moving vehicles. Importantly, the method works well with either panchromatic or multispectral images. The two accompanying case studies illustrate the use of the NGATE stereo image matcher in moving vehicle change detection, and removal of digital terrain model (DTM) defects caused by change or motion. Read the complete study >>