Tool Name	Feature Tracking
Tool ID	19
Library ID	grid_analysis
Version	1.2
Author(s)	M. Bremer, V. Wichmann (c) 2012-2026

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.
Two correlation methods are available: local normalized cross-correlation (NCC) and an FFT-based NCC approach. The latter is ported from the original Fortran implementation of the IMCORR software developed by the National Snow and Ice Data Center.
The FFT-based method computes correlations for all possible displacements simultaneously in the frequency domain, making it computationally efficient, particularly for large search areas. However, because the normalization is not strictly evaluated for each local window, the result is an approximation of true NCC.
In contrast, the local NCC method evaluates the correlation independently for each candidate displacement using window-specific statistics (mean and variance). It supports different kernel shapes and optional Gaussian weighting to reduce edge effects within the matching window. Although this approach is computationally more expensive, it provides greater robustness to local intensity variations and typically yields higher accuracy.
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 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.
Displacement Vector	shapes, output	CORRLINES	Line shapes layer with displacement vectors between correlated points.
Options
Correlation Method	choice	CORR_METHOD	Choose the correlation method to use.	Available Choices: [0] local NCC [1] FFT-based NCC Default: 0
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
Kernel Type	choice	KERNEL_TYPE	The kernel's shape.	Available Choices: [0] Square [1] Circle Default: 1
Weighting	choice	WEIGHTING	The kernel weighting.	Available Choices: [0] no weighting [1] Gaussian weighting 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