Arc by Tangents & IP

(This functionality is available with the Computations module)

Creates a new arc by specifying its tangent lines and any other arc parameter.

To run this option, select the Create/Arc command and the appropriate Method command from the Computations task to display the relevant dialog box.

The arc to be created will be given the attributes currently defined via the Attributes/Line command, and the associated tangent points created will be given the attributes currently defined via the Attributes/Point command. You should use these commands to set the required attributes before creating any arcs.

Note that if the tangent lines cross, it is possible to create the arc in any one of four quadrants. To specify the required quadrant, ensure that the order of the reference points is in the same direction as the arc.

Create Arc by Tangents

Item	Used to
Point ID	Key in the point identifier to be assigned to one of the new tangent points. The other new tangent point will get the next available identifier.
Tangent Line 1 & Tangent Line 2	Optionally select the tangent line with the mouse or key in the line number. If you select the line with the mouse (recommended), the reference points defining the selected line segment will automatically be placed in the Reference Points field. If however you key in the line number, you will still have to complete the Reference Points field. Note that you do not have to complete these tangent line fields, as just completing the reference points fields defines the tangents. Use the reference Points fields and not the Tangent Line fields if you do not want the arc inserted into a line object.
Reference Points (for each tangent line)	Specify the tangent line by two points. If you selected the tangent line in the Tangent Line field with the mouse, the Reference Points field will already be complete.
Fillet Lines	Select this option to have the tangent lines filleted at the tangent points when the arc is accepted. This will cause the tangent lines to be truncated or extended as the case may be such that they end at the tangent points. If a tangent line extends through the tangent points and the fillet option is not selected, it will be broken into two new lines that meet at the tangent point.
Interpolate Elevations	Select this option to interpolate elevations at the newly created tangent points.
Intersection Angle	Display the Intersection angle of the arc after the Compute button is selected.
Radio Buttons	Select which arc parameter is to be used in conjunction with the tangents to compute the arc. After making your selection, enter or specify the appropriate value.
Compute	Compute the arc and display it on the screen. All the arc parameters (radius, arc length etc.) will be displayed in the dialog. If any unusual circumstance occurs in the creation of the arc, a warning is also displayed on the dialog indicating the problem. For example, if the arc does not fit between the tangent lines entered, 'Warning - Arc beyond Reference Points' is displayed.
Accept	Save the computed arc to the database. Note that if the tangent lines were part of an alignment, the alignment is automatically modified to be along the new arc.
Next	Update the point identifier field to the next available unused point identifier greater than the point identifier currently shown.
Last	Update the point identifier field to one greater than the highest point identifier in the data base.