Compare statement

 Compare
   [Sce=reference_trial]
   [Tgt=target_trial]
   Mode=Psim|Ldist|Lang|Pdist|Plead|Mdiff
   [TimEq=time_equivalent]

Type conventions and statement syntax are explained in the Glossary.

Compares a target trial to a reference trial in the same document. The result of the comparison is stored as an internal array in which each point of the target trial is represented by an element.

Parameters...

Sce
Name parameter indicating the name of the trial which is to serve as the reference for the path comparison. Valid trial names are T01 through Tnn with nn being the number of trials in the case. Default = T01.

Tgt
Name parameter indicating the name of the trial whose path is to be compared to the reference. Valid trial names are T01 through Tnn with nn being the number of trials in the case. If this parameter is omitted, all trials in the case are compared to the reference, except the reference trial itself.

Mode
Radio button parameter indicating the comparison mode to be applied. There is no default, specify one of the following options:

• Psim = path similarity. For every point in the target trial, Wintrack scans the entire reference trial to find the reference point which lies closest to the target point in terms of distance. The spatial distance between the target and reference point is recorded as the result of the comparison.
• Ldist = distance between each point in the target trial and the closest line segment in the reference trial. The result is positive for target points that are to the right of the reference path.
• Lang = angle between the speed vector of each point in the target trial and the closest path segment in the reference trial. The result is positive if the deviation is counter-clockwise.

Comparison only when both target and reference point are selected:

• Pdist = distance in m between the current point in the target trial and the point with same calendar time in the reference trial.
• Plead = leading angle. For each pair of points with same calendar time in the reference and target trial, the composite movement direction is determined by adding the respective speed vectors (derived from vectors connecting respective next upstream to target and reference point). The leading angle is then defined as the angle between the composite speed vector and a vector pointing from the target point to the reference point. The result is 90° if the constellation of points does not permit to calculate a leading angle, eg. if target and reference point have identical position or if the composite movement vector is zero.
• Mdiff = comparison of cells in the current data matrix. Calculates difference between the cell referring to the current point in the target trial and the cell representing the point with same calendar time in the reference trial.

TimeEq
Number parameter indicating the time shift equivalent (m per sec time shift) for similarity calculation (Mode=Psim). Time shifts between geometrically related points can be penalized by transforming time differences into virtual distances which are added to the geometrical ones to decrease similarity. This transformation is determined by the time equivalent which tells Wintrack "how many meters to add per second of time difference". Penalization of time shifts can be based on absolute time stamp differences or on a running time shift. In the former case, each point in the target trial is considered separately. In the latter case, each time stamp difference is compared to that of the nearest upstream point and only the change in time stamp difference is penalized: This will distinguish between randomly shifted points and segments which are shifted as whole blocks. Specify 0 (default) to ignore time shifts. Specify positive values to penalize time shifts based on absolute time stamp differences. Specify negative values to penalize time shifts based on a running time shift.

Note that...

If no reference point with exactly matching calendar time is found during Pdist, Plead, and Mdiff comparisons, Wintrack uses linear interpolation to simulate a matching reference point. This is only a workaround, however, and exact results can only be obtained with synchronous data series.

After executing one or more Compare statements, you must execute the Matrix statement with Data=Compare to transfer the results of the path comparisons to the active data matrix. In the resulting data matrix, all trials which did not serve as comparison targets will contain only missing value codes.

Additional information...

• Managing custom variable definition files provides general information on the management of custom variable definition files.
• The Flowchart of advanced data analysis gives a synopsis of data and variable types.
• There is a topic describing how to build a custom variable definition file.
• There is a list of all available variable definition statements.
• See Analyze Case Document command for basic information on that command.
• Inside case documents provides advanced information on case documents.