December 2008 | Research and development

Simultaneous generation of DSM and DEM

Submitted by Dr. Bingcai Zhang, Engineering Fellow

NGATE can generate an accurate and dense digital surface model (DSM) that includes buildings, houses, trees, etc. from stereo images. In many applications, a digital elevation model (DEM) or bare-earth model is required. Transforming a DSM to a DEM is an expensive manual operation. In SOCET SET® v5.4.1, a number of new bare-earth tools were developed to speed up the DSM to DEM transformation. However, each tool is designed for a specific type of DSM and usually for a small area. Users still need to digitize a polygon to define an area. Most new bare-earth tools require a set of parameters and they are sensitive to these parameters. As a result, users may still need significant training and additional manual intervention for ideal results. In previous versions of NGATE, the “Eliminate Trees/Buildings/Other” option did not perform well.

Future development plans for NGATE in SOCET SET v5.5 and SOCET GXP v3.1 include capabilities for generating a DSM and DEM simultaneously. Initial tests based on three production projects indicate that the DSM is more accurate than the DSM generated with NGATE v5.4.1. Testing the NGATE v5.5 DEM shows that very few houses, buildings, and trees remained in the DEM while bare ground is preserved with high-quality and high-resolution images. The first project has 106 color images, 13824 by 7680 pixels, with a GSD of 0.248 feet. The project covers suburban areas of moderate terrain with many houses. Most houses and trees are removed from the DEM, while the DSM is more accurate than the DSM from v5.4.1 NGATE. The second project has 329 4-band images, 13824 by 7680 pixels, with a GSD of 0.2 meter. The project covers rural areas with many trees. Most of the trees are removed from the DEM while preserving the bare ground, even in very steep areas. The third project has 21 scanned color images, 19000 by 19000 pixels, with a GSD of 0.76 feet. It covers steep suburban areas with many buildings and houses. These are considered difficult areas for the DSM to DEM transformation.

Viewing these 3-D images requires red and blue anaglyph 3-D glasses. Cardboard anaglyph glasses can be purchased for about thirty cents from the following Web site: www.rainbowsymphony.com/freestuff.html

Figure 1. Project One. Top image is a DSM with two-foot contours; bottom image is a DEM with two-foot contours.

Figure 1. Project One. Top image is a DSM with two-foot contours; bottom image is a DEM with two-foot contours.

Figure 2. Project Two. Top image is a DSM with one-meter contours; bottom image is a DEM with one-meter contours.

Figure 2. Project Two. Top image is a DSM with one-meter contours; bottom image is a DEM with one-meter contours.

Figure 3. Project Three. DEM with five-meter contours.

Figure 3. Project Three. DEM with five-meter contours.

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