Comma Codes for Curving Lines

Curving:

There is often the requirement to display part or all a line feature as curved segments.  Kerbs in towns and cities are seldom straight.

The Curving comma code, normally C, specifies that the line feature generated using given points will be curved as long as it consists of a minimum of 3 points. If 'C' comma codes are only added to one segment of a line feature (2 points), a curve will not be created. Some examples are shown below.

The Tangent comma code, normally T, specifies that the line feature segment prior to or following the point is a tangent. If the prior segment is straight, the direction of this segment is used to constrain the start direction of the following segment.  If the prior segment is curved, the direction of the following segment is used to constrain the end direction of the prior segment.  Some examples are shown below.

Single Tangent	Double Tangent	Quadruple Tangent

The first of the examples above shows how a series of curved segments are followed by a straight segment using a tangent point.  The second shows how a single curved segment can be created between two straight line segments by using two tangent points.  The third shows how a 4-point polygon with four tangents can be used to simulate a pedestrian refuge in a road. 

The Discontinuity comma code, normally D, can stop and start curves at a designated point. In essence, two curves will start from a discontinuity point. The 'comma 'D' will give a sharp change in a curve appearing like a spearhead where the segments meet. 

To straighten segments, no comma code are applied. To carry out line straightening, you simply remove the comma codes inserted on the designated points and this will remove any curved or tangent lines created. You can chose to straighten a singular segment, between two specific points of a line feature or 'All' segments within a line feature. The image below is duplicated from the image used to show comma 'D' however in this case, 'All' segments have been straightened.