IMCORR - Feature Tracking

Author: M. Bremer, V. Wichmann (c) 2012-2026
Menu: Grid | Analysis

Description

The tool performs displacement analysis using image cross-correlation between two raster datasets. For each raster cell, a reference window and a search window are defined. The reference window extracts a template pattern, which is then matched within the larger search window. The algorithm identifies the correlation peak and uses its position to calculate the magnitude and direction of displacement. The maximum displacement of a feature that can be measured is: (search chip size/2 - reference chip size/2) * cell size This maximum applies only to exactly diagonal motion. In order to measure larger distances, a known offset between reference and search window can be given. The offset specifies the x/y components of the expected movement. Besides a constant offset, spatially variable offsets can be applied when a point shapes layer with start positions and x- and y-displacements, e.g. from a previous tool run, is provided. The tool can take two elevation models to query the elevations at the start and end points of the each detected movement to compute a 3D displacement vector. The tool has been ported to SAGA from the standalone IMCORR software developed by the National Snow and Ice Data Center in Boulder, Colorado, United States, and extended to take also elevation and spatially variable offsets into account. The tool computes the following attributes (some of them are only available if elevation data is provided):

ID: a unique identifier per measurement
GX, GY: grid column and row indices of the source (start) cell
REALX, REALY, REALZ: x,y,z world coordinates of the source (start) cell of the movement
DISP: horizontal displacement distance [map units]
DISP_REAL: 3D displacement distance [map units]
STRENGTH: correlation strength of the Fourier analysis [-]
FLAG: flag indicating a correlation was found [-]
XDISP, YDISP, ZDISP: x,y,z components of the displacement [map units]
XDISP_UNIT, YDISP_UNIT: x,y components of the displacement unit vector [0-1]
XTARG, YTARG, ZTARG: x,y,z world coordinates of the target (stop) cell of the movement
XERR, YERR: x,y error components of the correlation strength [-]
ASPECT, SLOPE: compass direction and gradient of the displacement [degree]
ID_M: identifier of the spatially variable measurement position (if specified)

Note: the tool requires that the input data does not contain any NoData cells.

References

Fahnestock, M. A., Scambos, T. A., and Bindschadler, R. A. (1992): Semi-automated ice velocity determination from satellite imagery. Eos, 73, 493.
Fey, C., Rutzinger, M., Wichmann, V., Prager, C., Bremer, M., and Zangerl, C. (2015): Deriving 3D displacement vectors from multi-temporal airborne laser scanning data for landslide activity analyses. GIScience & Remote Sensing, 52(4), 437-461. Link
Scambos, T. A., Dutkiewicz, M. J., Wilson, J. C., and Bindschadler, R. A. (1992): Application of image cross-correlation to the measurement of glacier velocity using satellite image data. Remote Sensing Environ., 42(3), 177-186. Link

Parameters

	Name	Type	Identifier	Description	Constraints
Input	Grid 1	grid, input	`GRID_1`	The first grid to correlate.	-
	Grid 2	grid, input	`GRID_2`	The second grid to correlate.	-
	DTM 1	grid, input, optional	`DTM_1`	The DEM used to extract elevation information for grid 1.	-
	DTM 2	grid, input, optional	`DTM_2`	The DEM used to extract elevation information for grid 2.	-
	Displacement Offsets	shapes, input	`SHP_OFFSET`	A point shapes layer with start positions and pre-calculated displacement offsets.	-
Output	Correlated Points	shapes, output	`CORRPOINTS`	Point shapes layer of correlated positions with displacement and correlation information.	-
Output	Displacement Vector	shapes, output	`CORRLINES`	Line shapes layer with displacement vectors between correlated points.	-
Options	Grid System	grid system	`PARAMETERS_GRID_SYSTEM`	-	-
	Search Chip Size	choice	`SEARCH_CHIPSIZE`	The size of the search chip (rectangular search area) used to find the correlating reference chip (pattern template) [cells].	Available Choices: [0] 32x32 [1] 64x64 [2] 128x128 [3] 256x256 Default: 1
	Reference Chip Size	choice	`REF_CHIPSIZE`	The size of the reference chip, i.e. the pattern template to find in search chip [cells].	Available Choices: [0] 16x16 [1] 32x32 [2] 64x64 [3] 128x128 Default: 1
	Stepping	integer number	`STEPPING`	The grid cell stepping used to move the search chip over the input grids [cells].	Minimum: 1 Default: 2
	Offset Type	choice	`OFFSET_TYPE`	Determines whether no offset between reference and search chip is applied, a uniform offset is used, or the offset varies across the spatial extent.	Available Choices: [0] no offset [1] constant offset [2] spatially variable offset Default: 0
	X Displacement	floating point number	`DISP_X`	The expected displacement in the x-direction (positive = east) [map units].	Default: 0.000000
	Y Displacement	floating point number	`DISP_Y`	The expected displacement in the y-direction (positive = north) [map units].	Default: 0.000000
	X Displacement	table field	`FIELD_DISP_X`	The attribute specifying the expected displacement in the x-direction (positive = east) [map units].	-
	Y Displacement	table field	`FIELD_DISP_Y`	The attribute specifying the expected displacement in the y-direction (positive = north) [map units].	-
	ID	table field	`FIELD_ID`	The identifier of the measurement position.	-
	Maximum Distance	floating point number	`MAX_DIST`	The maximum distance of a raster cell node to a pre-calculated start position [map units].	Minimum: 0.000000 Default: 4.000000

Command Line


Usage: saga_cmd grid_analysis 19 [-GRID_1 ] [-GRID_2 ] [-DTM_1 ] [-DTM_2 ] [-CORRPOINTS ] [-CORRLINES ] [-SEARCH_CHIPSIZE ] [-REF_CHIPSIZE ] [-STEPPING ] [-OFFSET_TYPE ] [-DISP_X ] [-DISP_Y ] [-SHP_OFFSET ] [-FIELD_DISP_X ] [-FIELD_DISP_Y ] [-FIELD_ID ] [-MAX_DIST ]
  -GRID_1:            Grid 1
	grid, input
  -GRID_2:            Grid 2
	grid, input
  -DTM_1:             DTM 1
	grid, input, optional
  -DTM_2:             DTM 2
	grid, input, optional
  -CORRPOINTS:        Correlated Points
	shapes, output
  -CORRLINES:         Displacement Vector
	shapes, output
  -SEARCH_CHIPSIZE:
                           Search Chip Size
                           	choice
                           	Available Choices:
                           	[0] 32x32
                           	[1] 64x64
                           	[2] 128x128
                           	[3] 256x256
                           	Default: 1
  -REF_CHIPSIZE:
                           Reference Chip Size
                           	choice
                           	Available Choices:
                           	[0] 16x16
                           	[1] 32x32
                           	[2] 64x64
                           	[3] 128x128
                           	Default: 1
  -STEPPING:          Stepping
	integer number
	Minimum: 1
	Default: 2
  -OFFSET_TYPE:
                           Offset Type
                           	choice
                           	Available Choices:
                           	[0] no offset
                           	[1] constant offset
                           	[2] spatially variable offset
                           	Default: 0
  -DISP_X:         X Displacement
	floating point number
	Default: 0.000000
  -DISP_Y:         Y Displacement
	floating point number
	Default: 0.000000
  -SHP_OFFSET:        Displacement Offsets
	shapes, input
  -FIELD_DISP_X:      X Displacement
	table field
  -FIELD_DISP_Y:      Y Displacement
	table field
  -FIELD_ID:          ID
	table field
  -MAX_DIST:       Maximum Distance
	floating point number
	Minimum: 0.000000
	Default: 4.000000