# Creating Points at Tangent Intersections

TPC uses the term Tangent intersections for intersections that are constrained to be tangent to an arc.

Given a curved survey line, TPC can determine where a line (originating from another point or tangent intersect) is tangent to that curved survey line.

## Example Take a look at the sample tangent instersection to the right.

We computed two tangent intersects,

• INT1R which is tangent to the  curve from 3PC to 3PT
• INT2R which is tangent to the curve from 7PC to 7PT

For this example, TPC computed tangent intersects at both ends of the red tangent line.

Here is the dialog used to compute this tangent-tangent intersect example. • We selected the Curve [>>] for Curve 1 then selected the arc from 3PC to 3PT in the drawing.
• Then we selected the Curve [>>] for Curve 2 then selected the arc from 7PC to 7PT.
• TPC activated the Right fields, indicating that it had computed these intersections.
• We choose Save and Plot for each of them.

## Tangent - Tangent Intersection

A Tangent-Tangent intersection, like the example shown here, computes intersections so that a line passing through them is tangent to both arcs.

## Tangent - Point Intersection

A Tangent-Point intersection, computes intersections so that a line passing through them and the point is tangent to the arc.

## Using the Tangent Intersection Dialog

• Choose COGO | Tangent Intersect to display the Tangent Intersect dialog.  See Accessing COGO.
• Enter the information you have for the intersection. If your intersection involves a curve that is already defined in the survey, enter the endpoints of the curve in the From and To fields.
• You can also use equations to enter a Radius based on any points in the survey. For example, to recall the distance between points 12 and 24, enter “12..24” in a Radius field.
• You can use the pick buttons [>] and [>>] to pick objects from a drawing. For example, to recall the radius of a drawing arc, pick that arc and select Radius from the pop-up list of values.
• Choose Save to save the computed points to the survey. They are not added to the survey when they are computed, only when you save them.
• To do another intersection, choose Clear.
• When you are finished creating intersection points, choose Close.

The Intersection dialog box will display the appopriate number of intersections based on the data you give it. When TPC finds a valid intersection, one or both Computed Intersection fields will be available for entry (white rather than gray).

Note: Computed Intersection fields will not be available if TPC can't find a valid intersection based on the data you entered.

## Naming Intersections

TPC names the computed intersections INT1L, INT1R, INT2L, INT2R. You can rename them as needed.

The 1L, 1R, 2L and 2R indicate the location and direction of the intersections as seen from Point 1 looking to Point 2.

So INT1R would be the tangent intersect for Point 1 as seen from Point 1 to Point 2.  INT2R would be the tangent intersect for Point 2 as seen from Point 1 to Point 2.

## Viewing the Computed Intersections

• Choose View. TPC will display the Point 1 line, the Point 2 line, and any computed intersection points. Use this information to decide which intersection point to save.

## Reporting the Comptued Intersections

• Choose Summary. TPC will summarize the data you provided and the intersections that were computed.

## Grid vs Ground / Geodetic

Intersections are computed based on the distance and direction types selected in the dialog.