GME

Geospatial Modelling Environment

movement.pathmetrics (Calculate Movement Path Metrics)

Calculates movement paths metrics (turn angles, step lengths, bearings, time intervals) for a point time series dataset

Description

This tool calculates turn angles, step lengths, bearings, and time intervals for a point time series dataset. The turn angle is based on the point sequence p(t-1), p(t), p(t+1); the step lengths, bearings and time intervals are based on the sequence p(t), p(t+1). Thus, a NoData value (-999) will be written for the first and last turn angles in a point series, and for the last step length, bearing and time interval records. These NoData values should obviously not be included in subsequent analyses.

If the optional radians parameter is set to TRUE then the turn angles and bearings are specified in radians (the default is degrees). The step length distances are always recorded in coordinate system units (e.g. meters for UTM). If the field name for any of the fields is set to NONE then that field will not be created. If names are not provided for these three fields then default names are used (TURNANGLE, STEPLENGTH, BEARING) and all three fields are calculated. In order to calculate time intervals (default field name: TIMEINTVL) you must specify a data/time field (datetimefield parameter). Shapefiles can be problematic for storing date/time data, so it is recommended that you use the geodatabase format for telemetry datasets.

The tool uses an integer order field to sort the points into the correct order (geodatabases are unordered collections, so must be ordered for time series analysis). Specifying an integer order field is compulsory as it eliminates the risk that incorrect data will be written because the order of the points is incorrect.

If an optional integer group field is specified then the command will sequentually process each unique value in that field, extracting all the points associated with that ID, sorting them, and writing the movement path metrics. The group field would be used when a point dataset contains multiple animals, for instance.

Syntax

movement.pathmetrics(in, uidfield, orderfield, [groupfield], [tafield], [slfield], [brgfield], [radians], [where], [datetimefield], [intervalfield]);

inthe input point data source
uidfieldthe name of the unique point ID field in the input data source
orderfieldthe name of the integer order field in the input data source
[groupfield]the name of the integer grouping field representing collections of points (e.g. an animal ID field)
[tafield]the turn angle field name to add (default=TURNANGLE; use NONE to disable)
[slfield]the step length field name to add (default=STEPLENGTH; use NONE to disable)
[brgfield]the bearing field name to add (default=BEARING; use NONE to disable)
[radians](TRUE/FALSE) specifies whether the turn angle and bearing are recorded as radians rather than degrees (default=FALSE)
[where]the selection statement that will be applied to the feature data source to identify a subset of features to process (see full Help documentation for further details)
[datetimefield]the field name of a date/time field (required if you specify an intervalfield)
[intervalfield]the time interval field to add (the interval in seconds between this record and the next; requires datetimefield is specified)

Example

movement.pathmetrics(in="C:\data\locs.shp", uidfield="PNTID", orderfield="ORDER");

movement.pathmetrics(in="C:\data\locs.shp", uidfield="PNTID", orderfield="ORDER", groupfield="ANIMALID", radians=TRUE);

movement.pathmetrics(in="C:\data\locs.shp", uidfield="PNTID", orderfield="ORDER", groupfield="ANIMALID", tafield="TURNS", slfield="STEPS", brgfield="NONE", datetimefield="RECDATE", intervalfield="TIMEINTVL", radians=TRUE);


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