This task performs RPC orthorectification using a Digital Surface Model (DSM) generated from a dense image matching method. The DSM is generated from two or more images taken from different view points, and it is used as the terrain source to orthorectify the first raster in the input rasters. For best results, put the raster closest to nadir view first.

This task requires a separate license for the ENVI Photogrammetry Module; contact your sales representative for more information.

Example

This example creates a DSM from an IKONOS stereo dataset. The source files are available from our ENVI Tutorials web page. Click the IKONOS Stereo link to download the .zip file to your machine, then unzip the files. The files you will use in this example are the Hobart*.* files. Update the file references in the example with the correct locations.

; Start the application
e = ENVI()
 
; Open  input files
File1 = 'HobartIKONOS1.dat'
File2 = 'HobartIKONOS2.dat'
 
Raster1 = e.OpenRaster(File1)
Raster2 = e.OpenRaster(File2)
 
; Get the task from the catalog of ENVITasks
Task = ENVITask('RPCOrthorectificationUsingDSMFromDenseImageMatching')
 
; Define inputs
Task.INPUT_RASTERS = [Raster1, Raster2]
 
; Run the task
Task.Execute
 
; Get the data collection
DataColl = e.Data
 
; Add the output to the data collection
DataColl.Add, Task.OUTPUT_RASTER
 
; Display the result
View = e.GetView()
Layer = View.CreateLayer(Task.OUTPUT_RASTER)
View.Zoom, /FULL_EXTENT

Syntax

Result = ENVITask('RPCOrthorectificationUsingDSMFromDenseImageMatching')

Input parameters (Set, Get): DO_BLOCK_ADJUSTMENT, EDGE_THRESHOLD, GRID_SPACING, INPUT_RASTERS, MATCHING_THRESHOLD, MINIMUM_OVERLAP, OUTPUT_COORDINATE_SYSTEM, OUTPUT_DSM_RASTER_URI, OUTPUT_PIXEL_SIZE, OUTPUT_RASTER_URI, QUALITY_THRESHOLD, RESAMPLING

Output parameters (Get only): OUTPUT_DSM_RASTER, 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

DO_BLOCK_ADJUSTMENT (optional)

Set this parameter to specify whether block adjustment will be applied before generating the DSM. The options are true (default) or false. A block, or bundle, adjustment is used to refine the 3D coordinates that describe the scene geometry. It finds a set of parameters that most accurately predict the locations of the observed points in a set of images, thus minimizing the reprojection error between image locations of observed and predicted image points. Applying a block adjustment for satellite images refines the image geometry to improve the quality of the DSM. If the the images have already been adjusted, set this parameter to false.

EDGE_THRESHOLD (optional)

Specify a value between 0 and 100. Set a lower value to include more mismatches in areas with poor contrast. Set a higher value to force rich texture and edge information in accepted matches. The default value is 5.

GRID_SPACING (optional)

Specify the grid spacing (in pixels) to use for orthorectification.

INPUT_RASTERS (required)

Specify an array of rasters from which to generate the DSM. The first raster will be orthorectified using the DSM. For best results, put the raster closest to nadir view first. The following rules apply to input stereo images:

  • They should have enough parallax, for example, stereo and tri-stereo images collected by sensors from different view points.
  • They must overlap by at least the percentage specified in the MINIMUM_OVERLAP parameter. The default value is 55 percent.
  • They must contain rational polynomial coefficients (RPCs) or physical sensor models. For satellite images, RPCs are preferred over physical models.
  • They must have the same number of bands. Select two or more panchromatic datasets, or select two or more multispectral datasets that have the same number of bands.
  • For other sensors not listed in the introduction of this topic, open the individual image files (TIFF, JPEG2000, or NITF) if available.

MATCHING_THRESHOLD (optional)

The match threshold sets a limit to the difference between matching windows. A value of 0 means no difference (a perfect match). Set this parameter to a lower value to increase confidence and to decrease mismatches. Set it to a higher value to capture finer details at the possible cost of more mismatches. The default value is 15.

MINIMUM_OVERLAP (optional)

Set this parameter to a percentage (0 to 100) indicating the minimum overlap area between two images, for matching to occur. Image pairs with a smaller overlap than the specified value are ignored.

The default value is 55.0000.

OUTPUT_COORDINATE_SYSTEM (optional)

Set this parameter to a valid ENVICoordSys object indicating the coordinate system to use for the orthorectified result. The default value is a UTM projection.

OUTPUT_DSM_RASTER_URI (optional)

Specify a string with the fully-qualified path and filename for OUTPUT_DSM_RASTER.

OUTPUT_PIXEL_SIZE (optional)

Set this parameter to a two-element array indicating the output X and Y pixel size for the orthorectified result, 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.

QUALITY_THRESHOLD (optional)

Specify a value between 0 and 100. Each pixel is assigned a quality measure, which is based on the similarity between windows around the pixel in the stereo images at the matched position. Setting this threshold to 0 will export all matched points for DSM generation. Increasing the threshold exports fewer matching points, but the quality of the DSM is potentially better.

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.

Output Parameters

OUTPUT_DSM_RASTER

This is a reference to the output DSM raster of filetype TIFF.

OUTPUT_RASTER

This is a reference to the output raster of filetype ENVI.

Methods

This task inherits the following methods from ENVITask:

AddParameter

Execute

Parameter

ParameterNames

RemoveParameter

Properties

DESCRIPTION

DISPLAY_NAME

NAME

REVISION

TAGS

Version History

ENVI 5.4

Introduced

ENVI 5.5.1

Added the OUTPUT_COORDINATE_SYSTEM parameter

See Also

ENVITask, RPCOrthorectification Task, RPCOrthorectificationUsingReferenceImage Task