The photogrammetric approach to digital elevation models
Probably one of the most important parts in the photogrammetric production process is the creation of a Digital Terrain Model or DTM. The DTM is used in the production of other data types such as orthophotos, and it is an important product in its own right. The quality of a DTM is dependent on various factors relating to flying specifications, pixel size, camera geometry and processing software parameters as well as degree of editing needed.
A Digital Elevation Model (DEM) is a generic term associated with a raster of elevation values. A DEM can be edited to generate a Digital Terrain Model (representation of a bare-earth model that contains elevations of natural terrain features where vegetation, buildings and other non-ground objects have been digitally removed), or a Digital Surface Model (which contains elevations of natural terrain in addition to top of buildings, trees and any other objects). Elevation models of all types are automatically interpolated from extremely dense 3D point clouds which are extracted from the imagery. Best accuracy is achieved by applying advanced algorithms for image matching and data filtering. The capture of break lines where appropriate is essential to obtain a perfect fit of a DTM with the real-world.
Aerometrex provides an unrivalled range of digital elevation products for a wide range of applications:
DTM Plus – Premium Digital Terrain Model of engineering accuracy
DTM Plus is our top of the range Digital Terrain Model. This product is a result from the interpolation of extremely dense 3D point clouds which are extracted from the imagery, coupled with skilled operator review in 3D. It is fully stereo-edited and 3D breaklines are captured at sharp changes of slope to obtain a perfect fit of the DTM with the real world. The absolute accuracy provided is suitable for engineering-type projects where accuracy is a critical factor.
- Hydrologically corrected
- Critically reviewed and edited in 3D stereo conditions
- Absolute accuracy of approx. 1.5 pixels at 2σ (95% confidence interval)
- Widest possible application of product
Stereo-edited Digital Terrain Model
Our regular Digital Terrain Model is a stereo-edited regular grid that represents the ‘bare-earth’ terrain free of buildings, vegetation and other non-ground objects. Major break-lines can be collected and supplied.
- Industry standard
- Fast processing of the data
- Absolute accuracy of 2.5 pixels at 2σ (95% confidence interval)
- Useful for environmental and planning applications
Fully automated Digital Terrain Model
Our fast Digital Terrain Model is a fully automated product. As with all of the above processes, raw 3D data is generated from aerial imagery by advanced stereo-correlation and image-matching software. Advanced automatic filtering algorithms are then applied to remove 3D points that may lay on top of buildings, vegetation and other non-ground objects.
- Define relief shapes
- Very quick processing time
- Cost-effective solution for large areas
DSM – Digital Surface Model
Our Digital Surface Models contain elevations of natural terrain in addition to top of buildings, trees and any other objects. This product is analogous to the LiDAR ‘first-return’ elevation model. It is suitable for line of sight analysis, building extraction and transmission line obstacle analysis. Aerometrex has generated large DSMs from some of its regular imagery coverages.
- Very dense grip of points
- Obstruction mapping and visibility analysis
- Nadir true ortho production input
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