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Coordinate directions are derived from Cartesian coordinates (Northings / Eastings) as opposed to geodetic directions which are derived from geodetic positions (Latitude / Longitude). Coordinate directions are referred to as Grid Bearing, Grid Azimuth.or just Bearing or North Az or South Az. Geodetic directions are always referred to as True Bearing or True Azimuth.
A survey can have one Coordinate Reference System (CRS) that relates it's geodetic positions and rectangular coordinates. TPC computes coordinate directions by inversing between coordinates on the current CRS and applying a convergence angle (also called a mapping angle) to generate a geodetic direction. Since the CRS relates the coordinates of a point to its geodetic position, TPC can compute both a coordinate direction and a geodetic direction between any two points.
Grid vs Geodetic North
Coordinate directions use convergence angles, also called mapping angles, to relate grid direction and geodetic direction. TPC keeps track of this for you as it displays and computes directions.
TPC uses NGS equations which transform between grid and geodetic positions. Convergence angles result from these computations which account for the geodetic position and projection parameters like central meridian and false easting.
Specifying a Direction Type
Advanced Traverse View Format dialog - you can choose which direction type to use for a particular traverse.
Miscellaneous Drawing Settings dialog - you can choose which direction type to use for line labels.
COGO dialogs - some COGO dialogs allow you to select which coordinate or geodetic direction type to display.
Grid Bearing (grid or local Cartesian coordinates)
This is the direction computed by inversing between grid coordinates. This is a planar computation of X/Y coordinate pairs using simple Cartesian trigonometry.
You can think of this grid as
•a local site grid with initial coordinates of 0/0 or 5000/5000
•the appropriate coordinate values for the CRS you have selected for the survey
Either way, TPC performs computations using Cartesian trigonometry.
The Traverse View status bar does not display any additional information about this direction type.
True Bearing (mean course convergence PLSS)
The option computes a mean scale direction for each course. It first computes the beginning and ending direction of the geodesic for the course, then averages them for the mean direction..
The Traverse View status bar displays “Mean course convergence”
True Bearing (mapping angle x°xx'xx") enter value
You may choose to enter your own mapping manually. If you have a special situation where the mapping able is specified for a particular traverse or or drawing, enter it here. Just select this option from the list then type the mapping angle right into the list field.
The Traverse View status bar displays "Mapping angle = x°xx'xx""
True Bearing (project mapping angle x°xx'xx"’)
This direction type uses the project mapping angle.
The Traverse View status bar displays "Project mapping angle = x°xx'xx"".
Related Topics
Choosing a Coordinate Reference System
CRS dialog
Scale Factors
Editions
Premium, Professional
Personal (grid direction only)
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