Preprocessing requirements

Before running this module, the following requirements must be met to ensure the job processes successfully and produces accurate results:

• Reference imagery: With this module you can automatically collect GCPs from reference imagery for the raw imagery being imported. To use reference imagery for automated GCP collection, ensure that the reference imagery provided is accurately georeferenced and provided in GDB-compatible format. For high-quality GCP collection, good practice dictates that the reference images have the highest level of accuracy possible, and be within a reasonable difference in spatial resolution to the raw imagery for which GCPs will be collected. While this requirement is not mandatory, it is important to make note of, to ensure a higher degree of accuracy in math-model refinement.

  You can specify a single reference file or a folder containing a set of orthorectified images. When you specify a folder, the module attempts to collect GCPs from all orthorectified images that have valid overlap with the given input image.

  Note: To improve performance, ensure that the reference imagery contains overviews (pyramids) by running the Pyramid module on all reference images prior to collecting GCPs.
• Digital elevation models: To use reference imagery in this module, you must supply a digital elevation model (DEM). The DEM must coincide with the area of interest and the reference imagery, and must be supplied in a GDB-compatible format. DEMs can be provided as a single file, or as multiple files or tiles covering the area of interest.

• Chip database: With this module, you can perform automated GCP collection from reference chip databases. A chip database is a compilation of individual image samples, called chips, usually measuring 256 pixels by 256 pixels or smaller. Each image section contains an accurate geocoded location and metadata, such as the sensor from which it was generated, the date it was acquired, the viewing angle, and so on.

  When working with a chip database, it is important to understand the limitations of automatic GCP collection from a chip database, with regards to the spatial resolution difference between the raw input scenes and the chip-database image chips. If there is a spatial resolution difference of more than a magnitude of five times, the results from automatic GCP collection from a chip database may be marginal. The chip database must be supplied in the PCI Geomatics Chip Database format.

• Polygon vector files: Polygon vector files can be supplied for automated GCP collection. These can be in a single file or in multiple files covering the area of interest. Polygon vector files should be provided in a GDB-compatible format.
• Road-network file: You can provide a vector road-network file (line) for automated GCP collection. This reference file can be used to automatically collect GCPs for roads in the area of interest. The road-network file must be supplied in a GDB-compatible format.
• Water-mask file: GCPs collected automatically by running this module can be refined using a water-mask file. This ensures that GCPs collected accidentally on a body of water are rejected. The water-mask file must be supplied in a GDB-compatible format.