Linear Directional Mean (Spatial Statistics)

Summary

Identifies the mean direction, length, and geographic center for a set of lines.

Usage

• The input must be a line feature class.

• Attribute values for the output line feature(s) include CompassA for Compass Angle (clockwise from due North), DirMean for Directional Mean (counterclockwise from due East), CirVar for Circular Variance (an indication of how much line directions or orientations deviate from the directional mean), AveX and AveY for Mean Center X and Y Coordinates, and AveLen for Mean Length. When a Case Field is specified, it also will be added to the Output Feature Class.

• Analogous to a standard deviation measure, the circular variance value tells how well the directional mean vector represents the set of input vectors. Circular variances range from 0 to 1. If all the input vectors have the exact same (or very similar) directions, the circular variance is small (near 0). When input vector directions span the entire compass, the circular variance is large (near 1).

• The Case Field is used to group features for separate linear directional mean computations. When a Case Field is specified, the input line features are first grouped according to case field values, and then an output line feature is created for each group. The case field can be of integer, date, or string type.

• When measuring direction, the tool only considers the first and last points in a line. The tool does not consider all of the vertices along a line.

• Map layers can be used to define the Input Feature Class. When using a layer with a selection, only the selected features are included in the analysis.

• When this tool runs in ArcMap, the output feature class is automatically added to the Table of Contents (TOC) with default rendering (directional vectors). The rendering applied is defined by a layer file in <ArcGIS>/ArcToolbox/Templates/Layers. You can reapply the default rendering, if needed, by importing the template layer symbology.

• Caution:

When using shapefiles, keep in mind that they cannot store null values. Tools or other procedures that create shapefiles from non-shapefile inputs may store or interpret null values as zero. This can lead to unexpected results. See also Geoprocessing considerations for shapefile output.

Syntax

DirectionalMean_stats (Input_Feature_Class, Output_Feature_Class, Orientation_Only, {Case_Field})
 Parameter Explanation Data Type Input_Feature_Class The feature class containing vectors for which the mean direction will be calculated. Feature Layer Output_Feature_Class A line feature class that will contain the features representing the mean directions of the input feature class. Feature Class Orientation_Only DIRECTION —The From and To node information is ignored. ORIENTATION_ONLY —The From and To nodes are utilized in calculating the mean (default). Boolean Case_Field(Optional) Field used to group features for separate directional mean calculations. The case field can be of integer, date, or string type. Field

Code Sample

LinearDirectionalMean Example (Python Window)

The following Python Window script demonstrates how to use the LinearDirectionalMean tool.

```import arcpy
arcpy.env.workspace = r"C:\data"
LinearDirectionalMean Example (stand-alone Python script)

The following stand-alone python script demonstrates how to use the LinearDirectionalMean tool.

```# Measure the geographic distribution of auto thefts

# Import system modules
import arcpy

# Local variables...
workspace = "C:/data"
locations = "AutoTheft.shp"
standardDistance = "auto_theft_SD.shp"
stardardEllipse = "auto_theft_SE.shp"
linearDirectMean = "auto_theft_LDM.shp"

try:
# Set the workspace (to avoid having to type in the full path to the data every time)
arcpy.env.workspace = workspace

# Process: Standard Distance of auto theft locations...
arcpy.StandardDistance_stats(locations, standardDistance, "1_STANDARD_DEVIATION", "#", "#")

# Process: Directional Distribution (Standard Deviational Ellipse) of auto theft locations...
arcpy.DirectionalDistribution_stats(locations, standardEllipse, "1_STANDARD_DEVIATION", "#", "#")

# Process: Linear Directional Mean of auto thefts...

except:
# If an error occurred while running a tool, print the messages
print arcpy.GetMessages()```

Environments

Output Coordinate System

Feature geometry is projected to the output coordinate system prior to analysis.

ArcView: Yes
ArcEditor: Yes
ArcInfo: Yes

3/7/2012