FilterTiePointsByGlobalTransformWithOrthorectification Task

This task uses the global transform to filter the tie points. For orthorectified images, nadir, or near-nadir images, the transformation model between the first image and the second image fits an RST transform. When the scene is rather flat and the sensor is very far from the scene, the transformation model between the two images fits a first-order polynomial transform. Global transform is the most common filtering method.

The following diagram shows where this task belongs within an image-to-image registration workflow:

References

Jin, Xiaoying. ENVI automated image registration solutions. NV5 Geospatial Solutions, Inc. whitepaper (2017). ENVI automated image registration solutions can be downloaded from our website.

Jin, Xiaoying, and Robert Schafer. Method and system for automatic registration of images. Exelis, Inc., assignee; now owned by NV5 Global, Inc. U.S. Patent No. 9,245,201 (issued January 26, 2016).

Example

This example uses sample Quickbird images and a USGS SRTM 1-arc second DEM. The files are available from our ENVI Tutorials web page. Click the Image Registration link to download the .zip file to your machine, then unzip the files.

; Start the application

e = ENVI()

; Open QuickBird images and SRTM 1-arc second DEM

file1 = 'QuickBirdPhoenixWest.dat'

raster1 = e.OpenRaster(file1)

file2 = 'QuickBirdPhoenixEast.dat'

raster2 = e.OpenRaster(file2)

DEMFile = 'PhoenixDEMSubset.dat'

DEMRaster = e.OpenRaster(DEMFile)

; Get the task from the catalog of ENVITasks

Task = ENVITask('GenerateTiePointsByCrossCorrelationWithOrthorectification')

; Define inputs

Task.INPUT_RASTER1 = raster1

Task.INPUT_RASTER2 = raster2

Task.INPUT_DEM_RASTER = DEMRaster

Task.REQUESTED_NUMBER_OF_TIEPOINTS = 40

; Run the task

Task.Execute

; Get the output tie points

TiePoints = Task.OUTPUT_TIEPOINTS

OrthoTiePoints = Task.OUTPUT_ORTHORECTIFIED_TIEPOINTS

; Get the tie point filter task from the catalog of ENVITasks

FilterTask = ENVITask('FilterTiePointsByGlobalTransformWithOrthorectification')

; Define inputs for the filtering task

FilterTask.INPUT_TIEPOINTS = TiePoints

FilterTask.INPUT_ORTHORECTIFIED_TIEPOINTS = OrthoTiePoints

; Run the task

FilterTask.Execute

; Define outputs for the filtering task

FilteredTiePoints = FilterTask.OUTPUT_TIEPOINTS

; Get the image-to-image registration task

RegTask = ENVITask('ImageToImageRegistration')

; Define inputs

RegTask.INPUT_TIEPOINTS = FilteredTiePoints

RegTask.WARPING = 'Triangulation'

; Run the image-to-image registration task

RegTask.Execute

; Get the output raster

WarpedRaster = RegTask.OUTPUT_RASTER

; Get the collection of data objects currently available in the Data Manager

DataColl = e.Data

; Add the output to the Data Manager

DataColl.Add, WarpedRaster

; Display the result

View = e.GetView()

Layer = View.CreateLayer(WarpedRaster)

Syntax

Result = ENVITask('FilterTiePointsByGlobalTransformWithOrthorectification')

Input properties (Set, Get): ERROR_THRESHOLD, FITTING_TRANSFORM, INPUT_ORTHORECTIFIED_TIEPOINTS, INPUT_TIEPOINTS, OUTPUT_TIEPOINTS_URI

Output properties (Get only): OUTPUT_TIEPOINTS

Properties marked as "Set" are those that you can set to specific values. You can also retrieve their current values any time. Properties marked as "Get" are those whose values you can retrieve but not set.

Methods

This task inherits the following methods from ENVITask:

Properties

This task inherits the following properties from ENVITask:

COMMUTE_ON_DOWNSAMPLE

ERROR_THRESHOLD (optional)

Specify the maximum error to allow for each tie point. The tie point with the largest error distance from the predicted location is iteratively removed until no tie points have an error greater than the this value. A first-order polynomial transform or RST transform is used to compute the predicted location from tie points on the first image to the points on the second image. The ERROR measurement represents the distance of each tie point in the second image to its predicted location, in pixel units. If at least one input image or warp image have RPC spatial reference and you specified a DEM file, ENVI performs an on-the-fly orthorectification on the input image(s) for geometric filtering by global transform, resulting in a more accurate image registration.

The default value is 5.0. A higher value keeps more tie points with larger fitting errors. If you prefer to keep most tie points, enter a high value such as 100.

FITTING_TRANSFORM (optional)

Specify the transform to use when automatically filtering tie points. The default is First-Order Polynomial.

First-Order Polynomial: A first-order polynomial warp includes an XY interaction term to account for image shear.
RST: Rotation, scaling, and translation; this is the simplest method. It does not allow for shearing in the image warp.

INPUT_ORTHORECTIFIED_TIEPOINTS (required)

This is a reference to the orthorectified tie points generated by the GenerateTiePointsByCrossCorrelationWithOrthorectification or GenerateTiePointsByMutualInformationWithOrthorectification task.

INPUT_TIEPOINTS (required)

This is a reference to an ENVITiePointSet object.

OUTPUT_TIEPOINTS

This is a reference to an ENVITiePointSet object with the output tie points.

OUTPUT_TIEPOINTS_URI (optional)

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

Version History

ENVI 5.2. 1

Introduced

API Version

4.2