# Circular Curve

> 2.0

Entity type is `kA3DTypeCrvCircle`.

The canonical form is defined with an `A3DMiscCartesianTransformationData`, its origin being the center of the circle and its vector X being the axis corresponding to zero parameter. The implicit parameterization is an angle expressed as radians in the range [0, 2PI].

`A3DParameterizationData`lets you specify reparameterization and trim.

Here are parameterization examples:

- To specify the interval in radians, set `m_dCoeffA`to 1.0 and `m_dCoeffB`to 0.0. These parameter values specify an identity conversion.
- To specify the interval in degrees, set `m_dCoeffA`to PI/180 and `m_dCoeffB`to 0.0. `m_dCoeffA`is the ratio of radians to degrees.

## Example of a circular arc

In the above example, the circular arc is in the XY plane (and therefore has an identity transformation), has radius R, and is restricted to the [ t0 , t1 ]interval.

If `m_dCoeffA`is 1.0 and `m_dCoeffB`is 0.0 and if the interval is defined as `t0=0`and `t1=PI/2`, then `t0`corresponds to the Cartesian coordinates (R,0,0) and `t1`to (0,R,0). These values for the `m_dCoeffA`and `m_dCoeffB`co-efficients indicate parameterization is in radians and starts at the X axis.

> Radius must be greater than 0.

> Radius as a parameter can be modified by `A3DMiscCartesianTransformationData`when the transformation defines uniform scaling.

Returns

> `A3D_SUCCESS`on success, or an error code on failure

Structures

- `A3DCrvCircleData`

Functions

- `A3DCrvCircleGet()`
- `A3DCrvCircleCreate()`

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