June 2009 | Q & A

What is the Automatic Terrain Generation module used for?

The Automatic Terrain Generation (ATG) module in SOCET GXP provides fully automated capabilities to extract elevation data from stereo imagery. The intuitive interface provides user-friendly options for creating accurate, high-resolution digital terrain models (DTM). In SOCET GXP, ATG natively generates SOCET GXP Grid, NITF, DTED, and GEOTIFF files, reducing editing and production time, while eliminating the need to import and export files.

SOCET GXP's ATG user interface

SOCET GXP’s ATG user interface

ATG consists of options for Automatic Terrain Extraction (ATE) and Next-Generation Automatic Terrain Extraction (NGATE). You select the method that is best-suited for the desired result.

What is the difference between ATE and NGATE?

ATE and NGATE are two options that can be used to create digital terrain models. Each uses a different algorithmic method to create the end result. The main difference is that NGATE generates a more-accurate and dense model. In SOCET GXP the output format of the DTM is a Grid; a two-dimensional array of elevation points called posts. The array of posts always is aligned north, south, east, and west with the coordinate system.

ATE performs image correlation on each post, whereas NGATE performs image correlation and edge-matching on each image pixel. Users control ATE speed by using large post spacing to reduce the number of posts. With NGATE, speed is controlled by stopping the application at a different minification level using different precision and speed options; speed is not dependent on post spacing or number of posts.

ATE is most useful for producing low-density models over rural and other non-developed areas. Functionality is available for seed DTM integration and bare-earth technology is included for removing trees and buildings. Batch capabilities also are provided. More posts require more processing time. ATE can produce models as dense as approximately 15 times the image ground sample distance; as density increases, the speed advantage of ATE declines.

NGATE is best for large-scale imagery in urban areas. ATE is not effective at distinguishing buildings from the ground. Therefore, the model climbs up over building roofs. NGATE DTM quality in those difficult areas is far better than that from ATE. As a result, NGATE can significantly reduce editing time.

NGATE almost always produces a more accurate model than ATE. If speed is important to production, you can change speed and precision options to generate the model faster than ATE with slightly better accuracy. If the desired product is an accurate and dense model, NGATE always performs better than ATE.

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