How To: Orthorectify raster products
Orthorectification is the process of removing distortions in imagery caused by the sensor and terrain to create a planimetric image at every location with consistent scale across all parts of the image. More information about orthorectification is available in the following help topic: Fundamentals of orthorectifying a raster dataset.
One of the strengths of a raster product is the ability to orthorectify the imagery if an RPC file is included. ArcGIS is designed to automatically consume the RPC file, if one is available, by applying the Geometric Function. Until a DEM is supplied, the orthorectification is based on a constant elevation. The Geometric Function is automatically applied both when working with a raster product directly, and when adding it to a mosaic dataset. More information is available from the following help topic: Geometric function.
Orthorectification is only possible if the raster product includes a Rational Polynomial Coefficient (RPC) file, which contains all the necessary information to use in conjunction with elevation data to orthorectify imagery. More information about the RPC file can be found in the following help topic: Fundamentals of orthorectifying a raster dataset. In addition to the RPC file, having a DEM to use produces the most accurate results. A constant elevation value, such as the average elevation, can be used in place of a DEM, but the results may not be as accurate.
When the raster product metadata file is added to ArcMap or a mosaic dataset, the RPC information is automatically pulled from the RPC file and used to orthorectify the image. The RPC file must be stored in the same folder as the metadata file for this to work.
Specifying Elevation Directly With The Raster Product
1. Browse to the raster product folder in Catalog or the Add Data dialog.
2. Add the raster dataset that displays the satellite icon to ArcMap.
3. Right-click the raster product name in the Table of Contents and click Properties.
4. Select the Functions tab to display the Geometric Function included as part of the function chain.
5. Right-click the Geometric Function and open the Properties dialog.
6. In the Raster Function Properties dialog, select the Geometric tab.
7. Verify that the information from the RPC file is being applied to the orthorectification by clicking the Geodata Transform button.
An elevation value is assigned by default and can be changed using the 'Constant Z' parameter under the Geometric tab in the Raster Function Properties dialog. This is also where a DEM can be assigned to use for orthorectification instead of a constant elevation value.
Specifying Elevation With A Mosaic Dataset
The Geometric Function works the same for raster products in a mosaic dataset, but it is important to be aware that it is applied at the raster dataset level and not the mosaic dataset level. This is because each source dataset may have its own RPC file associated with it.
To take advantage of a raster product in a mosaic dataset, it is necessary to specify the correct Product Definition and Raster Type.
To access the Geometric Function for a raster product in a mosaic dataset, use the following procedure:
1. Add the mosaic dataset to ArcMap.
2. Open the attribute table for the Footprint layer.
3. Go to the correct record for the specific raster product of interest.
4. Click the cell in the Raster field to display a little chevron symbol.
5. Click the chevron button to open the properties dialog for the raster product.
6. Select the Functions tab to display Geometric Function in the function chain.
7. The procedure for specifying elevation data is the same as the above for working with the raster product.