matplotlib.patches.
Arc
(xy, width, height, angle=0.0, theta1=0.0, theta2=360.0, **kwargs)[source]¶Bases: matplotlib.patches.Ellipse
An elliptical arc. Because it performs various optimizations, it can not be filled.
The arc must be used in an Axes
instance---it can not be added directly to a
Figure
---because it is optimized to
only render the segments that are inside the axes bounding box
with high resolution.
The following args are supported:
If theta1 and theta2 are not provided, the arc will form a complete ellipse.
Valid kwargs are:
Property Description agg_filter
a filter function, which takes a (m, n, 3) float array and a dpi value, and returns a (m, n, 3) array alpha
float or None animated
bool antialiased
unknown capstyle
{'butt', 'round', 'projecting'} clip_box
Bbox
clip_on
bool clip_path
[( Path
,Transform
) |Patch
| None]color
color contains
callable edgecolor
color or None or 'auto' facecolor
color or None figure
Figure
fill
bool gid
str hatch
{'/', '\', '|', '-', '+', 'x', 'o', 'O', '.', '*'} in_layout
bool joinstyle
{'miter', 'round', 'bevel'} label
object linestyle
{'-', '--', '-.', ':', '', (offset, on-off-seq), ...} linewidth
float or None for default path_effects
AbstractPathEffect
picker
None or bool or float or callable rasterized
bool or None sketch_params
(scale: float, length: float, randomness: float) snap
bool or None transform
Transform
url
str visible
bool zorder
float
draw
(renderer)[source]¶Ellipses are normally drawn using an approximation that uses eight cubic Bezier splines. The error of this approximation is 1.89818e-6, according to this unverified source:
Lancaster, Don. Approximating a Circle or an Ellipse Using Four Bezier Cubic Splines.
There is a use case where very large ellipses must be drawn with very high accuracy, and it is too expensive to render the entire ellipse with enough segments (either splines or line segments). Therefore, in the case where either radius of the ellipse is large enough that the error of the spline approximation will be visible (greater than one pixel offset from the ideal), a different technique is used.
In that case, only the visible parts of the ellipse are drawn, with each visible arc using a fixed number of spline segments (8). The algorithm proceeds as follows:
The points where the ellipse intersects the axes bounding box are located. (This is done be performing an inverse transformation on the axes bbox such that it is relative to the unit circle -- this makes the intersection calculation much easier than doing rotated ellipse intersection directly).
This uses the "line intersecting a circle" algorithm from:
Vince, John. Geometry for Computer Graphics: Formulae, Examples & Proofs. London: Springer-Verlag, 2005.
The angles of each of the intersection points are calculated.
Proceeding counterclockwise starting in the positive x-direction, each of the visible arc-segments between the pairs of vertices are drawn using the Bezier arc approximation technique implemented in
matplotlib.path.Path.arc()
.
matplotlib.patches.Arc
¶