For successful DSM results the PhotoModeler project needs to be high quality. This means using a properly calibrated camera, and ensuring the project has a low maximum residual (under 1.0 pixels preferably, or under about 2.0 pixels if using SmartMatch) before proceeding with DSM processing.
In some cases, the project also needs an ‘extents’ definition. That is, a definition of the region in the photos to be scanned. This is generally not required for MVS. There are three options:
• Most common and the simplest approach is to use DSM Trims to define one or more trim regions, where you draw one or more polygonal regions in one or more of the photos. PhotoModeler will restrict the DSM based on the trim region defined (note the trim’s properties will dictate whether the inside (“Trim outside boundary”), or outside (i.e. “Cut hole”) of the trim boundary will be used in the search process).
• In some situations you may opt to use the entire image boundary to define the DSM extents. The DSM will cover the area that is common to both photos.
• In other situations (e.g. weaker projects, or if an initial DSM is too noisy) you may get a better result by defining an approximate Surface in the project to guide the DSM algorithm. This Surface needs to appear on the pairs of photos but can extend off the photos. The DSM will be confined to the approximate boundaries of this surface which allows you to control how much of a surface is modeled. If you want to create a DSM that is larger than the approximate surface, you will need to extend the surface. One way of doing this is to use Surface Draw to define new boundaries outside of the original surface, then use the new Surface Draw boundaries to define a new larger surface. See DSM Approximate Surfaces.
Pair-based DSM also needs to know how far to search in the images. This is given to it by the approximating surface and depth range values in the DSM Dialog. The approximating surface can be created automatically during the DSM run (using already solved 3D points in the project, such as the point cloud generated from SmartMatch) or you can create a Surface and select it before going into the DSM Dialog. If the latter explicit Surface is used it will be the same Surface as the one described in step 3 above for the extents definition. If you are using the automatic/implicit surface then no further project work is required and you can proceed to run the DSM algorithm (by opening the DSM Options Dialog).