Station Offsets

TPC is just as comfortable working with stations offsets as it is working with coordinates. Once an alignment is established, points can be both located  and computed by station and offset based on that alignment.

OFS Point Type

Traverses can utilize the OFS (Offset) point type to locate station/offset points.

Offset points always follow a point on the alignment that establishes the distance along the alignment per the stationing of the alignment. The distance to the offset point is then the prependicular (shortest) distance from the offset point to the corresponding alignment point. You can have any number of offset points following an alignment point, but each one originates fromt he shared alignment point.

Offsets points are also unique in that TPC completely controls the direction of the offset based on the alignment. It does this by computing a direction that is perpendicular to the alignment at the alignment point or by bisecting the angle if the offset if from an alignment angle point.

Offsets From Points of Tangency

TPC examines points of tangency (before and after curves and spirals) to determine if they are tangent. If so, the offset is perpendicular and lies in the direction of the corresponding radius point. If not, TPC computes the offset-intersection of the alignment for the offset position. This can involve some pretty serious mathematics in the case of spirals, but TPC does a good job of locating the offset points.

COGO Station Offset Command

The Station Offsets command inserts two points into the current traverse at the requested station. One is the station point along the alignment. The other is the offset point from that station.

The Tolerance field tells TPC not to create a new station point if the survey already has a point within the tolerance of the specified station.

Offsets from an Existing Point

You can add an offset point to an existing station (any control point on an alignment). You can enter any combination of horizontal distance, slope distance, etc. TPC computes the bearing from the position of the alignment station, and uses the information you enter to compute the position of the offset point.

Grid vs Ground / Geodetic

The stations are computed based on the distance type of the traverse.

For example, if an alignment traverse is formatted for ground distance at project elevation, the computed station and offset will be ground distance at project elevation.


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Related Topics

Using COGO
COGO Commands
Entering Stations
Creating Station Offsets
Creating Stations at Intervals
Entering Stations and Equations
Creating Offsets to an Alignment
Creating a Station/Offset Report