This .NET class wraps the AcDbDiametricDimension ObjectARX class. It represents the diameter dimension type in AutoCAD. 

This dimension type requires two points that define a diameter chord on the curve being dimensioned to be able to draw the dimension line from one chord point to the other. In addition, if the text is located outside the curve being dimensioned, then a "leader length" value is used to determine how far the dimension line extends out past the curve before doing a horizontal dogleg (if necessary) to the annotation text.

Autodesk.AutoCAD.DatabaseServices.DBObject
    Autodesk.AutoCAD.DatabaseServices.Entity
        Autodesk.AutoCAD.DatabaseServices.Dimension
            Autodesk.AutoCAD.DatabaseServices.DiametricDimension

Public Class DiametricDimension
Inherits Dimension

public class DiametricDimension : Dimension;

When a newly created dimension entity is first closed, an anonymous block (an BlockTableRecord that contains all the appropriate line, arc, arrowhead solids, text, and others, and with *D as the block name prefix) will automatically be created for it to reference for display. 

The LeaderLength property is only used during the creation of the dimension (and even then only if the dimension is set to use the default text position value). After the dimension is closed for the first time, changing the LeaderLength value will not affect how the dimension displays. However, the new setting will be stored and will show up in DXF and AutoLISP. 

If the dimension is set to use the text position value rather than the default text position, then the text position will take precedence over both the ChordPoint and FarChordPoint properties, as well as the LeaderLength value, in placing the dimension line so it will be positioned properly relative to the text position. 

When creating an DiametricDimension for which the dimension line must align with the ChordPoint and FarChordPoint, set the dimension to use the default text position and use the leaderLength to position the text. 

If the text position is more important than the chord points, then set the dimension to ignore the default text position and set the text position as desired.

DBObject, Entity