This task performs a refined Rational Polynomial Coefficient (RPC) orthorectification by automatically generating Ground Control Points (GCPs) from a reference image.
Example
This example uses sample images from the RPC Orthorectification tutorial. Tutorial files are available from our ENVI Tutorials web page. Click the RPC Ortho link to download the .zip file to your machine, then unzip the files. Update the file references in the example with the correct locations.
e = ENVI()
inputFile = 'OrbViewSubset.dat'
inputRaster = e.OpenRaster(inputFile)
referenceFile = 'NAIPReferenceImage.dat'
referenceRaster = e.OpenRaster(referenceFile)
DEMFile = 'DEM.dat'
DEMRaster = e.OpenRaster(DEMFile)
Task = ENVITask('RPCOrthorectificationUsingReferenceImage')
Task.INPUT_RASTER = inputRaster
Task.INPUT_REFERENCE_RASTER = referenceRaster
Task.INPUT_DEM_RASTER = DEMRaster
Task.Execute
View = e.GetView()
Layer = View.CreateLayer(Task.OUTPUT_RASTER)
View.Zoom, /FULL_EXTENT
Syntax
Result = ENVITask('RPCOrthorectificationUsingReferenceImage')
Input parameters (Set, Get): DEM_IS_HEIGHT_ABOVE_ELLIPSOID, GRID_SPACING, INPUT_DEM_RASTER, INPUT_RASTER, INPUT_REFERENCE_RASTER, OUTPUT_COORDINATE_SYSTEM, OUTPUT_GCPS_URI, OUTPUT_PIXEL_SIZE, OUTPUT_RASTER_URI, REQUESTED_NUMBER_OF_GCPS, RESAMPLING, SEARCH_WINDOW
Output parameters (Get only): OUTPUT_GCPS, OUTPUT_RASTER
Parameters marked as "Set" are those that you can set to specific values. You can also retrieve their current values any time. Parameters marked as "Get" are those whose values you can retrieve but not set.
Input Parameters
DEM_IS_HEIGHT_ABOVE_ELLIPSOID (optional)
Set this parameter to true if the DEM is already expressed as the height above the ellipsoid and no geoid correction is required. Most DEM data contain orthometric heights, which are elevations above mean sea level (for example, GMTED2010 or National Elevation Dataset, NED). In these cases, keep the default selection of false.
GRID_SPACING (optional)
Specify the grid spacing (in pixels) to use for orthorectification. The default value is 10.
INPUT_DEM_RASTER (required)
Specify a digital elevation model (DEM) raster. A DEM raster is only required if the input raster has an RPC sensor model. It must have valid map information. If you do not have a DEM file readily available, you can use the global DEM named GMTED2010.jp2 that is provided under the ENVI installation folder. The Global Multi-resolution Terrain Elevation Data 2010 (GMTED2010) has a mean resolution of 30 arc seconds.
INPUT_RASTER (required)
Specify a raster with an RPC spatial reference.
INPUT_REFERENCE_RASTER (required)
Specify a reference image from which to match and find the geographic coordinates of the GCPs. The reference raster should be a true orthorectified image with the same or slightly higher spatial resolution than the input raster. Try to choose a reference image that is close to the year and season of the input raster. Automatic GCP generation is based on image matching between the reference image and source image, so the scene contents should not be vastly different. Automatic GCP generation is more robust if the reference image and input image have similar resolution. If the reference image has a much higher resolution than the input image (i.e., the ratio is greater than 2.5), consider down-sampling the reference image first.
OUTPUT_COORDINATE_SYSTEM (optional)
Set this parameter to a valid ENVICoordSys object indicating the coordinate system to use. The default value is a UTM projection.
OUTPUT_GCPS_URI (optional)
Specify a string with the fully qualified path and filename for OUTPUT_GCPS.
OUTPUT_PIXEL_SIZE (optional)
Specify a two-element array indicating the output X and Y pixel size, in the units defined by OUTPUT_COORDINATE_SYSTEM. The default value is the pixel size of the input image.
OUTPUT_RASTER_URI (optional)
Specify a string with the fully qualified filename and path of the associated OUTPUT_RASTER.
- If you do not specify this parameter, or set it to an exclamation symbol (!), ENVI creates a temporary file.
- If you set it to the hash symbol (#), ENVI creates a file in the temporary directory, but this file will not be deleted when ENVI closes.
REQUESTED_NUMBER_OF_GCPS (optional)
Specify the requested number of GCPs. The default value is 25.
RESAMPLING (optional)
Specify the resampling method to use when creating the spatial grid:
- Nearest Neighbor (default): Uses the nearest pixel without any interpolation.
- Bilinear: Performs a linear interpolation using four pixels to resample.
- Cubic Convolution: Uses 16 pixels to approximate the sinc function using cubic polynomials to resample the image.
SEARCH_WINDOW (optional)
Specify the search window size. Increase the value if there is a big misalignment between the input raster and the reference raster.
Output Parameters
OUTPUT_GCPS
This is a reference to the output GCPs.
OUTPUT_RASTER
This is a reference to the output raster of filetype ENVI.
Methods
Execute
Parameter
ParameterNames
Properties
DESCRIPTION
DISPLAY_NAME
NAME
REVISION
TAGS
Version History
ENVI 5.3. 1 |
Introduced |
ENVI 5.3.2 |
Added the OUTPUT_PIXEL_SIZE parameter
|
ENVI 5.4.1 |
Input rasters can have a replacement sensor model (RSM) or an RPC sensor model. The INPUT_RASTER and DEM_RASTER descriptions were updated.
|
ENVI 5.4.2 |
Added the SEARCH_WINDOW parameter
|
ENVI 5.5.1 |
Added the OUTPUT_COORDINATE_SYSTEM parameter
|
See Also
ENVITask, GenerateGCPsFromReferenceImage Task, GenerateGCPsFromTiePoints Task, ENVIGCPSet, ENVITiePointSet, RPCOrthorectification Task, RPCOrthorectificationUsingDSMFromDenseImageMatching Task