Calculate Grid Convergence Angle (Cartography)

Summary

Calculates the rotation angle for true north based on the center point of each feature in a feature class and populates this value in a specified field. This field can be used in conjunction with Data Driven Pages to rotate each map to true north.

Usage

Legacy:

This tool replaces the Calculate Geodesic Angle tool.

• Calculating a geodesic angle requires that a valid projected coordinate system is specified.
  • If you specify a coordinate system field, the tool will use the projected coordinate system value (projection engine string) for each feature. If there is an invalid projection engine string, the tool will then use coordinate system specified as the Cartographic coordinate system environment variable.
  • If you are not using a field to specify the projected coordinate system, the tool will use the one specified as the Cartographic coordinate system in the Cartography environment settings.

Syntax

CalculateGridConvergenceAngle_cartography (in_features, angle_field, {rotation_method}, {coordinate_sys_field})

Parameter	Explanation	Data Type
in_features	Input feature class (points, multipoints, lines, and polygons).	Feature Layer
angle_field	Existing field that will be populated with the true north calculation value in decimal degrees.	Field
rotation_method (Optional)	Method in which the rotation value is calculated. Geographic is the default value. GEOGRAPHIC —Angle is calculated clockwise with 0 at top. This is the default. ARITHMETIC —Angle is calculated counterclockwise with 0 at right. GRAPHIC —Angle is calculated counterclockwise with 0 at top.	String
coordinate_sys_field (Optional)	Field containing a projection engine string for a projected coordinate system to be used for angle calculation. The angle calculation for each feature will be based on the projected coordinate system projection engine string for the specific feature. In cases where there is an invalid value the tool will use the Cartographic coordinate system specified in the Cartography environment settings. The default is none, or no field specified. When no field is specified, the projected coordinate system used for calculation will be taken from the Cartography environment settings.	Field

Code Sample

CalculateGridConvergenceAngle tool example 1 (Python window)

Calculates a true north rotation angle for a feature.

import arcpy
from arcpy import env
arcpy.env.workspace = "C:\data\ProjectData.gdb"
arcpy.CalculateGridConvergenceAngle_cartography ("US_states", "angle", "GEOGRAPHIC", "UTM")

CalculateGridConvergenceAngle tool example 2 (stand-alone Python script)

Calculates a true north rotation angle for point features.

# Name: calculategridconvergenceangle_example.py
# Description: Calculates the true north rotation angle for features
# Author: ESRI

# Import system modules
import arcpy
from arcpy import env

# Set environment settings
arcpy.env.workspace = "C:\Data\ProjectData.gdb"

# Set local variables
inFeatures = "US_states"
angleField = "angle"
rotationMethod = "GEOGRAPHIC"
coordSystemField = "UTM"

# Execute CalculateGridConvergenceAngle
arcpy.CalculateGridConvergenceAngle_cartography(inFeatures, angleField,
                                                rotationMethod,
                                                coordSystemField)

Environments

Cartographic Coordinate System, Current Workspace

Cartographic Coordinate System

This setting is used when no coordinate system field is chosen, or if a coordinate system field is chosen and the coordinate system string value is invalid, in which case the coordinate system specified here will be used in the angle calculation.

Licensing Information

ArcGIS for Desktop Basic: Yes

ArcGIS for Desktop Standard: Yes

ArcGIS for Desktop Advanced: Yes