Traverse Point Types

A traverse is a collection of points that belong together for some reason. By combining the sequence of points with the traverse Point Types, you can achieve just about any combination of data you want.

Point Types

Here is a list of the point types you may see in a traverse

(blank) Occupied Point / Foresight / Control Point - you see this a lot as you enter deed descriptions or your field data (GPS or conventional)
SS Sideshot
SSM Sideshot Mean - derived from an angle set
BS Backsight
BM Benchmark
RS Resection
OFS Offset (perpendicular)
OFX Cross-Section
OBS Observation used to create redundancy for Least Squares networks
PI Point of Intersection (horizontal tangent intersect)
PC - Point of Curvature, compound curvature or reverse curvature of a horizontal curve
PT - Point of Tangency of a horizontal curve
BC - Beginning of Curve of a vertical curve
EC - End of Curve of a vertical curve
VPI - Vertical Point of Intersection (vertical tangent intersect)
TS - Tangent to Spiral
SC - Spiral to Curve
CS - Curve to Spiral
ST - Spiral to Tangent
F1, F2, F4, B1, B2 - angle set components
FSM Foresight Mean derived from an angle set
Note A note inserted between two other traverse points
Gap GAP point tells TPC not to draw the line or labels at this location

Specifying a Point Type

Point types are specified in the Traverse View by choosing Edit | Point Type and selecting a type from the list. Most of the types have hot keys and there is also a Point Type toolbar available in the Traverse View. The point type you select is applied to each selected (highlighted) point in the Traverse View, so it's easy to change multiple points with one command.

Control Point

A control point is a very general point type in TPC that simply indicates that this point is used as the starting position for any subsequent computations. Any additional points added to the traverse are computed from this control point. So a control point could be followed by 20 sideshots, each of which is computed from that control point. When another control point is entered, additional points added to the traverse are computed from it.

Point      Type    Raw Data         
1                                                Point 1 is the first control point, from which the sideshots 100 and 101 are computed.
2           BS                                Point 2 is the backsight used to orient the following shots.
100       SS       yes 
101       SS       yes
33                                                 Point 3 is the next control point from which the sideshot 102 is computed.
102       SS       yes                     Point 2 is assumed to be the backsight because no other BS point was specified.

Control points do not display a Point Type in a traverse unless they are part of a hoizontal or vertical curve (i.e. PC, PT, BC, EC, PI, TS, SC, CS, ST).

BS - Backsight

Backsights are use for conventional surveys (total station or theodolite). Unless a backsight point is specified, TPC always assumes that the previous control point is the backsight. You can confirm this by selecting any horizontal angle in a traverse and reading the Status bar where TPC will display 'BS=xx". It also assumes that the backsight circle reading is zero (you zero'd the gun on the backsight)

You include a backsight point in TPC for any of these reasons:

Foresights

Foresights are just another form of Control Point in TPC that contains Raw Data used to compute the position of the foresight (from the previous Control Point) then establish the foresight as the next control point. This creates an ambiguous situation since the foresight could display FS to indicate it is a foresight or be left blank to indicate it is a Control Point. As a result, TPC does not display FS for the Point Type, but leaves it blank like any other Control Point.

The one exception is when the foresight has been computed from an angle set. In this case, TPC displays FSM, indicating that is is a Foresight Mean.

SS - Sideshot

A sideshot always originates from the previous control point but no other points are computed from it. You can always recall any sideshot later on as a control point, but in the current sequence, it is the end of the line. See Entering Sideshots.

The sideshot point type also determines how the point is drawn when the traverse is tagged in a drawing. All sideshots and offsets are drawn using the traverse's Sideshot settings.

SSM - Sideshot Mean

When a sideshot is derived from an angle set, TPC displays SSM instead of SS to indicate that the displayed data is the mean of the angle set's observations.

BM - Benchmark

A benchmark is an observation to a point of known elevation. TPC computes the elevation difference to the total station, thereby establishing it's elevation independent of the control point's elevation. The Instrument Height displayed is actually the computed difference between the elevation of the gun and the control point.

The benchmark shot always follows the backsight shot.

RS - Resection

Resections are shots taken to other control points, who's positions are known, in order to establish the position of their preceding control point.

You can include any number of resection shots after a control point. If only two resections points are included, TPC does a standard 2-point resection. If more are included, TPC does a simple Least Squares resection.

OFS - Offset

An offset point is a special kind of sideshot. Like a sideshot, it originates from the previous control point then stops. Unlike a sideshot, the direction component (azimuth, bearing or horizontal angle) is optional. If an Offset includes a directional component, it is computed just like a sideshot.

However, if an Offset does not have a directional component, it assumes that the offset it perpendicular to the alignment created by the control points. Offsets are capable of bisecting the angle if the control points define tangents and is capable of computing perpendicular offsets to curves and spirals where appropriate. In this case, the sign of the distance data is used to compute the side of the alignment the offset is on. Positive distances compute offsets to the right. Negative distances compute offsets to the left.

The nice thing about Offsets is that if the alignment changes, the Offsets recompute their positions automatically to remain perpendicular to the alignment.

OFX - Cross-Section

Cross section points can not be created in this version but are supported from previous versions. A cross section point works just like an Offset but originates from the previous Control Point, Offset or Cross Section point.

OBS - Observation

An observation is any point that contains data but does not actually compute its point. All of the angle set types (F1, F2, etc) are observations. They hold data for an angle set but don't actually compute the point until they are meaned.

The OBS point type indicates an observation that is not part of an angle set. Like any observation, they contain raw data measured to a point but do not compute that point. OBS points are used to build redundancy for Least Squares computations.

PI - Point of Intersection

A Point of Intersection is a special kind of Control Point that defines the central angle of a curve or spiral by its incoming and outgoing tangents. Designating a Control Point as a PI does not change the central angle it merely tells TPC that the included central angle is available for curve and spiral computations. So you can enter one more piece of curve data, like a radius, and TPC has everything it needs to compute the curve. Or enter additional spiral information and TPC has everything it needs to compute the spiral.

In addition, PI's have the ability to float in their curve points. When you enter a radius for a PI, TPC automatically inserts the corresponding PC and PT for the resulting curve into the traverse. Change the radius value and the inserted PC and PT float along their respective tangents to match the resulting curve.

PI points are incredible time saves when you are trying to fit an existing alignment.

F1, F2, F4, B1, B2 - angle set components

These point types are components of a horizontal angle set. They are always followed by a SSM (sideshot mean) or FSM (foresight mean) point.

FSM - Foresight Mean

A Foresight Mean is a special kind of Control Point that includes Raw Data generated from the preceding angle set.

Note

A Note is a special kind of description that is not tied to a specific point, but rather is part of the traverse's point sequence. Many data collectors use notes to store information about the field data being collected.

Gap

When you insert a Gap point into a traverse, you are telling TPC not to draw the line or labels at this location. In other words, you are creating a gap.

Related Topics

Traverses