Preparing a DEM for airphoto orthorectification

Orthorectifying airphotos requires a digital elevation model (DEM) to correct geometry and relief-displacement. This requirement is central for airphoto orthorectification. The three general workflows for providing a DEM for airphoto orthorectification are described herein.

Workflow I

You have a DEM that is readily available for airphoto orthorectification. The only potential task you may need to complete is to create a DEM index file. For information on doing so, see Creating a DEM index file.

Figure 1. Workflow I: Preparing a DEM

CATALYST Enterprise Aerial Preparing a DEM 1

Workflow II

You have a DEM generated from three-dimensional (3-D) vector or LiDAR data for airphoto orthorectification. The 3-D vector data, generated from previous projects or perhaps a government agency, is often available in ESRI Shape file format, DLG format, or as x, y, and z points in a text file. Vector data can include:

Mass points
Contours
Break lines
Building models
Lake polygons
Cliffs and valleys
Bridges

Figure 2. Workflow II: Preparing a DEM

CATALYST Enterprise Aerial Preparing a DEM 2

In CATALYST Enterprise, you can combine hundreds—even thousands—of vector-data files to create a high-accuracy raster digital surface model (DSM) or digital terrain model (DTM), depending on the content of the data.

CATALYST Enterprise also supports the American Society for Photogrammetry and Remote Sensing (ASPRS) Light Detection and Ranging (LiDAR) LAS file format version 1.0, and treats each LiDAR return number as a separate vector layer. If the LiDAR data contains surface-model points, the resulting raster DSM can be converted automatically to a DTM or edited manually with DEM Editing in CATALYST Professional Focus.

The prerequisite for this workflow is at least one of the aforementioned vector data types or a LiDAR LAS file.

For information on generating a DEM, see Generating a DEM.

Workflow III

You have a DEM extracted from stereo-image pairs for airphoto orthorectification.

The prerequisites for workflow 3 are a project with an adequate aerial-triangulation solution and sufficient overlap between the images.

Figure 3. Workflow III: Preparing a DEM

CATALYST Enterprise Aerial Preparing a DEM 3

For information on extracting a DEM from stereo-image pairs, see Extracting a DEM from stereo-image pairs.