# Polygons¶

class sympy.geometry.polygon.Polygon[source]

A two-dimensional polygon.

A simple polygon in space. Can be constructed from a sequence of points or from a center, radius, number of sides and rotation angle.

Parameters

vertices : sequence of Points

Raises

GeometryError

If all parameters are not Points.

Notes

Polygons are treated as closed paths rather than 2D areas so some calculations can be be negative or positive (e.g., area) based on the orientation of the points.

Any consecutive identical points are reduced to a single point and any points collinear and between two points will be removed unless they are needed to define an explicit intersection (see examples).

A Triangle, Segment or Point will be returned when there are 3 or fewer points provided.

Examples

>>> from sympy import Point, Polygon, pi
>>> p1, p2, p3, p4, p5 = [(0, 0), (1, 0), (5, 1), (0, 1), (3, 0)]
>>> Polygon(p1, p2, p3, p4)
Polygon(Point2D(0, 0), Point2D(1, 0), Point2D(5, 1), Point2D(0, 1))
>>> Polygon(p1, p2)
Segment2D(Point2D(0, 0), Point2D(1, 0))
>>> Polygon(p1, p2, p5)
Segment2D(Point2D(0, 0), Point2D(3, 0))


The area of a polygon is calculated as positive when vertices are traversed in a ccw direction. When the sides of a polygon cross the area will have positive and negative contributions. The following defines a Z shape where the bottom right connects back to the top left.

>>> Polygon((0, 2), (2, 2), (0, 0), (2, 0)).area
0


When the the keyword $$n$$ is used to define the number of sides of the Polygon then a RegularPolygon is created and the other arguments are interpreted as center, radius and rotation. The unrotated RegularPolygon will always have a vertex at Point(r, 0) where $$r$$ is the radius of the circle that circumscribes the RegularPolygon. Its method $$spin$$ can be used to increment that angle.

>>> p = Polygon((0,0), 1, n=3)
>>> p
RegularPolygon(Point2D(0, 0), 1, 3, 0)
>>> p.vertices[0]
Point2D(1, 0)
>>> p.args[0]
Point2D(0, 0)
>>> p.spin(pi/2)
>>> p.vertices[0]
Point2D(0, 1)


Attributes

 area angles perimeter vertices centroid sides
property angles

The internal angle at each vertex.

Returns

angles : dict

A dictionary where each key is a vertex and each value is the internal angle at that vertex. The vertices are represented as Points.

Examples

>>> from sympy import Point, Polygon
>>> p1, p2, p3, p4 = map(Point, [(0, 0), (1, 0), (5, 1), (0, 1)])
>>> poly = Polygon(p1, p2, p3, p4)
>>> poly.angles[p1]
pi/2
>>> poly.angles[p2]
acos(-4*sqrt(17)/17)

arbitrary_point(parameter='t')[source]

A parameterized point on the polygon.

The parameter, varying from 0 to 1, assigns points to the position on the perimeter that is that fraction of the total perimeter. So the point evaluated at t=1/2 would return the point from the first vertex that is 1/2 way around the polygon.

Parameters

parameter : str, optional

Default value is ‘t’.

Returns

arbitrary_point : Point

Raises

ValueError

When $$parameter$$ already appears in the Polygon’s definition.

Examples

>>> from sympy import Polygon, S, Symbol
>>> t = Symbol('t', real=True)
>>> tri = Polygon((0, 0), (1, 0), (1, 1))
>>> p = tri.arbitrary_point('t')
>>> perimeter = tri.perimeter
>>> s1, s2 = [s.length for s in tri.sides[:2]]
>>> p.subs(t, (s1 + s2/2)/perimeter)
Point2D(1, 1/2)

property area

The area of the polygon.

Notes

The area calculation can be positive or negative based on the orientation of the points. If any side of the polygon crosses any other side, there will be areas having opposite signs.

Examples

>>> from sympy import Point, Polygon
>>> p1, p2, p3, p4 = map(Point, [(0, 0), (1, 0), (5, 1), (0, 1)])
>>> poly = Polygon(p1, p2, p3, p4)
>>> poly.area
3


In the Z shaped polygon (with the lower right connecting back to the upper left) the areas cancel out:

>>> Z = Polygon((0, 1), (1, 1), (0, 0), (1, 0))
>>> Z.area
0


In the M shaped polygon, areas do not cancel because no side crosses any other (though there is a point of contact).

>>> M = Polygon((0, 0), (0, 1), (2, 0), (3, 1), (3, 0))
>>> M.area
-3/2

property bounds

Return a tuple (xmin, ymin, xmax, ymax) representing the bounding rectangle for the geometric figure.

property centroid

The centroid of the polygon.

Returns

centroid : Point

Examples

>>> from sympy import Point, Polygon
>>> p1, p2, p3, p4 = map(Point, [(0, 0), (1, 0), (5, 1), (0, 1)])
>>> poly = Polygon(p1, p2, p3, p4)
>>> poly.centroid
Point2D(31/18, 11/18)

cut_section(line)[source]

Returns a tuple of two polygon segments that lie above and below the intersecting line respectively.

Parameters

line: Line object of geometry module

line which cuts the Polygon. The part of the Polygon that lies above and below this line is returned.

Returns

upper_polygon, lower_polygon: Polygon objects or None

upper_polygon is the polygon that lies above the given line. lower_polygon is the polygon that lies below the given line. upper_polygon and lower polygon are None when no polygon exists above the line or below the line.

Raises

ValueError: When the line does not intersect the polygon

Examples

>>> from sympy import Point, Symbol, Polygon, Line
>>> a, b = 20, 10
>>> p1, p2, p3, p4 = [(0, b), (0, 0), (a, 0), (a, b)]
>>> rectangle = Polygon(p1, p2, p3, p4)
>>> t = rectangle.cut_section(Line((0, 5), slope=0))
>>> t
(Polygon(Point2D(0, 10), Point2D(0, 5), Point2D(20, 5), Point2D(20, 10)),
Polygon(Point2D(0, 5), Point2D(0, 0), Point2D(20, 0), Point2D(20, 5)))
>>> upper_segment, lower_segment = t
>>> upper_segment.area
100
>>> upper_segment.centroid
Point2D(10, 15/2)
>>> lower_segment.centroid
Point2D(10, 5/2)


References

https://github.com/sympy/sympy/wiki/A-method-to-return-a-cut-section-of-any-polygon-geometry

distance(o)[source]

Returns the shortest distance between self and o.

If o is a point, then self does not need to be convex. If o is another polygon self and o must be convex.

Examples

>>> from sympy import Point, Polygon, RegularPolygon
>>> p1, p2 = map(Point, [(0, 0), (7, 5)])
>>> poly = Polygon(*RegularPolygon(p1, 1, 3).vertices)
>>> poly.distance(p2)
sqrt(61)

encloses_point(p)[source]

Return True if p is enclosed by (is inside of) self.

Parameters

p : Point

Returns

encloses_point : True, False or None

Notes

Being on the border of self is considered False.

Examples

>>> from sympy import Polygon, Point
>>> from sympy.abc import t
>>> p = Polygon((0, 0), (4, 0), (4, 4))
>>> p.encloses_point(Point(2, 1))
True
>>> p.encloses_point(Point(2, 2))
False
>>> p.encloses_point(Point(5, 5))
False


References

first_moment_of_area(point=None)[source]

Returns the first moment of area of a two-dimensional polygon with respect to a certain point of interest.

First moment of area is a measure of the distribution of the area of a polygon in relation to an axis. The first moment of area of the entire polygon about its own centroid is always zero. Therefore, here it is calculated for an area, above or below a certain point of interest, that makes up a smaller portion of the polygon. This area is bounded by the point of interest and the extreme end (top or bottom) of the polygon. The first moment for this area is is then determined about the centroidal axis of the initial polygon.

Parameters

point: Point, two-tuple of sympifyable objects, or None (default=None)

point is the point above or below which the area of interest lies If point=None then the centroid acts as the point of interest.

Returns

Q_x, Q_y: number or sympy expressions

Q_x is the first moment of area about the x-axis Q_y is the first moment of area about the y-axis A negetive sign indicates that the section modulus is determined for a section below (or left of) the centroidal axis

Examples

>>> from sympy import Point, Polygon, symbol
>>> a, b = 50, 10
>>> p1, p2, p3, p4 = [(0, b), (0, 0), (a, 0), (a, b)]
>>> p = Polygon(p1, p2, p3, p4)
>>> p.first_moment_of_area()
(625, 3125)
>>> p.first_moment_of_area(point=Point(30, 7))
(525, 3000)


References

intersection(o)[source]

The intersection of polygon and geometry entity.

The intersection may be empty and can contain individual Points and complete Line Segments.

Parameters

other: GeometryEntity

Returns

intersection : list

The list of Segments and Points

Examples

>>> from sympy import Point, Polygon, Line
>>> p1, p2, p3, p4 = map(Point, [(0, 0), (1, 0), (5, 1), (0, 1)])
>>> poly1 = Polygon(p1, p2, p3, p4)
>>> p5, p6, p7 = map(Point, [(3, 2), (1, -1), (0, 2)])
>>> poly2 = Polygon(p5, p6, p7)
>>> poly1.intersection(poly2)
[Point2D(1/3, 1), Point2D(2/3, 0), Point2D(9/5, 1/5), Point2D(7/3, 1)]
>>> poly1.intersection(Line(p1, p2))
[Segment2D(Point2D(0, 0), Point2D(1, 0))]
>>> poly1.intersection(p1)
[Point2D(0, 0)]

is_convex()[source]

Is the polygon convex?

A polygon is convex if all its interior angles are less than 180 degrees and there are no intersections between sides.

Returns

is_convex : boolean

True if this polygon is convex, False otherwise.

Examples

>>> from sympy import Point, Polygon
>>> p1, p2, p3, p4 = map(Point, [(0, 0), (1, 0), (5, 1), (0, 1)])
>>> poly = Polygon(p1, p2, p3, p4)
>>> poly.is_convex()
True

property perimeter

The perimeter of the polygon.

Returns

perimeter : number or Basic instance

Examples

>>> from sympy import Point, Polygon
>>> p1, p2, p3, p4 = map(Point, [(0, 0), (1, 0), (5, 1), (0, 1)])
>>> poly = Polygon(p1, p2, p3, p4)
>>> poly.perimeter
sqrt(17) + 7

plot_interval(parameter='t')[source]

The plot interval for the default geometric plot of the polygon.

Parameters

parameter : str, optional

Default value is ‘t’.

Returns

plot_interval : list (plot interval)

[parameter, lower_bound, upper_bound]

Examples

>>> from sympy import Polygon
>>> p = Polygon((0, 0), (1, 0), (1, 1))
>>> p.plot_interval()
[t, 0, 1]

polar_second_moment_of_area()[source]

Returns the polar modulus of a two-dimensional polygon

It is a constituent of the second moment of area, linked through the perpendicular axis theorem. While the planar second moment of area describes an object’s resistance to deflection (bending) when subjected to a force applied to a plane parallel to the central axis, the polar second moment of area describes an object’s resistance to deflection when subjected to a moment applied in a plane perpendicular to the object’s central axis (i.e. parallel to the cross-section)

Examples

>>> from sympy import Polygon, symbols
>>> a, b = symbols('a, b')
>>> rectangle = Polygon((0, 0), (a, 0), (a, b), (0, b))
>>> rectangle.polar_second_moment_of_area()
a**3*b/12 + a*b**3/12


References

https://en.wikipedia.org/wiki/Polar_moment_of_inertia

second_moment_of_area(point=None)[source]

Returns the second moment and product moment of area of a two dimensional polygon.

Parameters

point : Point, two-tuple of sympifyable objects, or None(default=None)

point is the point about which second moment of area is to be found. If “point=None” it will be calculated about the axis passing through the centroid of the polygon.

Returns

I_xx, I_yy, I_xy : number or sympy expression

I_xx, I_yy are second moment of area of a two dimensional polygon. I_xy is product moment of area of a two dimensional polygon.

Examples

>>> from sympy import Point, Polygon, symbols
>>> a, b = symbols('a, b')
>>> p1, p2, p3, p4, p5 = [(0, 0), (a, 0), (a, b), (0, b), (a/3, b/3)]
>>> rectangle = Polygon(p1, p2, p3, p4)
>>> rectangle.second_moment_of_area()
(a*b**3/12, a**3*b/12, 0)
>>> rectangle.second_moment_of_area(p5)
(a*b**3/9, a**3*b/9, a**2*b**2/36)


References

https://en.wikipedia.org/wiki/Second_moment_of_area

section_modulus(point=None)[source]

Returns a tuple with the section modulus of a two-dimensional polygon.

Section modulus is a geometric property of a polygon defined as the ratio of second moment of area to the distance of the extreme end of the polygon from the centroidal axis.

Parameters

point : Point, two-tuple of sympifyable objects, or None(default=None)

point is the point at which section modulus is to be found. If “point=None” it will be calculated for the point farthest from the centroidal axis of the polygon.

Returns

S_x, S_y: numbers or SymPy expressions

S_x is the section modulus with respect to the x-axis S_y is the section modulus with respect to the y-axis A negetive sign indicates that the section modulus is determined for a point below the centroidal axis

Examples

>>> from sympy import symbols, Polygon, Point
>>> a, b = symbols('a, b', positive=True)
>>> rectangle = Polygon((0, 0), (a, 0), (a, b), (0, b))
>>> rectangle.section_modulus()
(a*b**2/6, a**2*b/6)
>>> rectangle.section_modulus(Point(a/4, b/4))
(-a*b**2/3, -a**2*b/3)


References

https://en.wikipedia.org/wiki/Section_modulus

property sides

The directed line segments that form the sides of the polygon.

Returns

sides : list of sides

Each side is a directed Segment.

Examples

>>> from sympy import Point, Polygon
>>> p1, p2, p3, p4 = map(Point, [(0, 0), (1, 0), (5, 1), (0, 1)])
>>> poly = Polygon(p1, p2, p3, p4)
>>> poly.sides
[Segment2D(Point2D(0, 0), Point2D(1, 0)),
Segment2D(Point2D(1, 0), Point2D(5, 1)),
Segment2D(Point2D(5, 1), Point2D(0, 1)), Segment2D(Point2D(0, 1), Point2D(0, 0))]

property vertices

The vertices of the polygon.

Returns

vertices : list of Points

Notes

When iterating over the vertices, it is more efficient to index self rather than to request the vertices and index them. Only use the vertices when you want to process all of them at once. This is even more important with RegularPolygons that calculate each vertex.

Examples

>>> from sympy import Point, Polygon
>>> p1, p2, p3, p4 = map(Point, [(0, 0), (1, 0), (5, 1), (0, 1)])
>>> poly = Polygon(p1, p2, p3, p4)
>>> poly.vertices
[Point2D(0, 0), Point2D(1, 0), Point2D(5, 1), Point2D(0, 1)]
>>> poly.vertices[0]
Point2D(0, 0)

class sympy.geometry.polygon.RegularPolygon[source]

A regular polygon.

Such a polygon has all internal angles equal and all sides the same length.

Parameters

center : Point

radius : number or Basic instance

The distance from the center to a vertex

n : int

The number of sides

Raises

GeometryError

If the $$center$$ is not a Point, or the $$radius$$ is not a number or Basic instance, or the number of sides, $$n$$, is less than three.

Notes

A RegularPolygon can be instantiated with Polygon with the kwarg n.

Regular polygons are instantiated with a center, radius, number of sides and a rotation angle. Whereas the arguments of a Polygon are vertices, the vertices of the RegularPolygon must be obtained with the vertices method.

Examples

>>> from sympy.geometry import RegularPolygon, Point
>>> r = RegularPolygon(Point(0, 0), 5, 3)
>>> r
RegularPolygon(Point2D(0, 0), 5, 3, 0)
>>> r.vertices[0]
Point2D(5, 0)


Attributes

 vertices center radius rotation apothem interior_angle exterior_angle circumcircle incircle angles
property angles

Returns a dictionary with keys, the vertices of the Polygon, and values, the interior angle at each vertex.

Examples

>>> from sympy import RegularPolygon, Point
>>> r = RegularPolygon(Point(0, 0), 5, 3)
>>> r.angles
{Point2D(-5/2, -5*sqrt(3)/2): pi/3,
Point2D(-5/2, 5*sqrt(3)/2): pi/3,
Point2D(5, 0): pi/3}

property apothem

Returns

apothem : number or instance of Basic

Examples

>>> from sympy import Symbol
>>> from sympy.geometry import RegularPolygon, Point
>>> rp = RegularPolygon(Point(0, 0), radius, 4)
>>> rp.apothem
sqrt(2)*r/2

property area

Returns the area.

Examples

>>> from sympy.geometry import RegularPolygon
>>> square = RegularPolygon((0, 0), 1, 4)
>>> square.area
2
>>> _ == square.length**2
True

property args

Returns the center point, the radius, the number of sides, and the orientation angle.

Examples

>>> from sympy import RegularPolygon, Point
>>> r = RegularPolygon(Point(0, 0), 5, 3)
>>> r.args
(Point2D(0, 0), 5, 3, 0)

property center

The center of the RegularPolygon

This is also the center of the circumscribing circle.

Returns

center : Point

Examples

>>> from sympy.geometry import RegularPolygon, Point
>>> rp = RegularPolygon(Point(0, 0), 5, 4)
>>> rp.center
Point2D(0, 0)

property centroid

The center of the RegularPolygon

This is also the center of the circumscribing circle.

Returns

center : Point

Examples

>>> from sympy.geometry import RegularPolygon, Point
>>> rp = RegularPolygon(Point(0, 0), 5, 4)
>>> rp.center
Point2D(0, 0)

property circumcenter

Alias for center.

Examples

>>> from sympy.geometry import RegularPolygon, Point
>>> rp = RegularPolygon(Point(0, 0), 5, 4)
>>> rp.circumcenter
Point2D(0, 0)

property circumcircle

The circumcircle of the RegularPolygon.

Returns

circumcircle : Circle

Examples

>>> from sympy.geometry import RegularPolygon, Point
>>> rp = RegularPolygon(Point(0, 0), 4, 8)
>>> rp.circumcircle
Circle(Point2D(0, 0), 4)

property circumradius

Examples

>>> from sympy import Symbol
>>> from sympy.geometry import RegularPolygon, Point
>>> rp = RegularPolygon(Point(0, 0), radius, 4)
r

encloses_point(p)[source]

Return True if p is enclosed by (is inside of) self.

Parameters

p : Point

Returns

encloses_point : True, False or None

Notes

Being on the border of self is considered False.

The general Polygon.encloses_point method is called only if a point is not within or beyond the incircle or circumcircle, respectively.

Examples

>>> from sympy import RegularPolygon, S, Point, Symbol
>>> p = RegularPolygon((0, 0), 3, 4)
>>> p.encloses_point(Point(0, 0))
True
>>> p.encloses_point(Point((r + R)/2, 0))
True
>>> p.encloses_point(Point(R/2, R/2 + (R - r)/10))
False
>>> t = Symbol('t', real=True)
>>> p.encloses_point(p.arbitrary_point().subs(t, S.Half))
False
>>> p.encloses_point(Point(5, 5))
False

property exterior_angle

Measure of the exterior angles.

Returns

exterior_angle : number

Examples

>>> from sympy.geometry import RegularPolygon, Point
>>> rp = RegularPolygon(Point(0, 0), 4, 8)
>>> rp.exterior_angle
pi/4

property incircle

The incircle of the RegularPolygon.

Returns

incircle : Circle

Examples

>>> from sympy.geometry import RegularPolygon, Point
>>> rp = RegularPolygon(Point(0, 0), 4, 7)
>>> rp.incircle
Circle(Point2D(0, 0), 4*cos(pi/7))

property inradius

Alias for apothem.

Examples

>>> from sympy import Symbol
>>> from sympy.geometry import RegularPolygon, Point
>>> rp = RegularPolygon(Point(0, 0), radius, 4)
sqrt(2)*r/2

property interior_angle

Measure of the interior angles.

Returns

interior_angle : number

Examples

>>> from sympy.geometry import RegularPolygon, Point
>>> rp = RegularPolygon(Point(0, 0), 4, 8)
>>> rp.interior_angle
3*pi/4

property length

Returns the length of the sides.

The half-length of the side and the apothem form two legs of a right triangle whose hypotenuse is the radius of the regular polygon.

Examples

>>> from sympy.geometry import RegularPolygon
>>> from sympy import sqrt
>>> s = square_in_unit_circle = RegularPolygon((0, 0), 1, 4)
>>> s.length
sqrt(2)
>>> sqrt((_/2)**2 + s.apothem**2) == s.radius
True

property radius

This is also the radius of the circumscribing circle.

Returns

radius : number or instance of Basic

Examples

>>> from sympy import Symbol
>>> from sympy.geometry import RegularPolygon, Point
>>> rp = RegularPolygon(Point(0, 0), radius, 4)
r

reflect(line)[source]

Override GeometryEntity.reflect since this is not made of only points.

Examples

>>> from sympy import RegularPolygon, Line

>>> RegularPolygon((0, 0), 1, 4).reflect(Line((0, 1), slope=-2))
RegularPolygon(Point2D(4/5, 2/5), -1, 4, atan(4/3))

rotate(angle, pt=None)[source]

Override GeometryEntity.rotate to first rotate the RegularPolygon about its center.

>>> from sympy import Point, RegularPolygon, Polygon, pi
>>> t = RegularPolygon(Point(1, 0), 1, 3)
>>> t.vertices[0] # vertex on x-axis
Point2D(2, 0)
>>> t.rotate(pi/2).vertices[0] # vertex on y axis now
Point2D(0, 2)


rotation

spin

Rotates a RegularPolygon in place

property rotation

CCW angle by which the RegularPolygon is rotated

Returns

rotation : number or instance of Basic

Examples

>>> from sympy import pi
>>> from sympy.abc import a
>>> from sympy.geometry import RegularPolygon, Point
>>> RegularPolygon(Point(0, 0), 3, 4, pi/4).rotation
pi/4


Numerical rotation angles are made canonical:

>>> RegularPolygon(Point(0, 0), 3, 4, a).rotation
a
>>> RegularPolygon(Point(0, 0), 3, 4, pi).rotation
0

scale(x=1, y=1, pt=None)[source]

Override GeometryEntity.scale since it is the radius that must be scaled (if x == y) or else a new Polygon must be returned.

>>> from sympy import RegularPolygon


Symmetric scaling returns a RegularPolygon:

>>> RegularPolygon((0, 0), 1, 4).scale(2, 2)
RegularPolygon(Point2D(0, 0), 2, 4, 0)


Asymmetric scaling returns a kite as a Polygon:

>>> RegularPolygon((0, 0), 1, 4).scale(2, 1)
Polygon(Point2D(2, 0), Point2D(0, 1), Point2D(-2, 0), Point2D(0, -1))

spin(angle)[source]

Increment in place the virtual Polygon’s rotation by ccw angle.

>>> from sympy import Polygon, Point, pi
>>> r = Polygon(Point(0,0), 1, n=3)
>>> r.vertices[0]
Point2D(1, 0)
>>> r.spin(pi/6)
>>> r.vertices[0]
Point2D(sqrt(3)/2, 1/2)


rotation

rotate

Creates a copy of the RegularPolygon rotated about a Point

property vertices

The vertices of the RegularPolygon.

Returns

vertices : list

Each vertex is a Point.

Examples

>>> from sympy.geometry import RegularPolygon, Point
>>> rp = RegularPolygon(Point(0, 0), 5, 4)
>>> rp.vertices
[Point2D(5, 0), Point2D(0, 5), Point2D(-5, 0), Point2D(0, -5)]

class sympy.geometry.polygon.Triangle[source]

A polygon with three vertices and three sides.

Parameters

points : sequence of Points

keyword: asa, sas, or sss to specify sides/angles of the triangle

Raises

GeometryError

If the number of vertices is not equal to three, or one of the vertices is not a Point, or a valid keyword is not given.

Examples

>>> from sympy.geometry import Triangle, Point
>>> Triangle(Point(0, 0), Point(4, 0), Point(4, 3))
Triangle(Point2D(0, 0), Point2D(4, 0), Point2D(4, 3))


Keywords sss, sas, or asa can be used to give the desired side lengths (in order) and interior angles (in degrees) that define the triangle:

>>> Triangle(sss=(3, 4, 5))
Triangle(Point2D(0, 0), Point2D(3, 0), Point2D(3, 4))
>>> Triangle(asa=(30, 1, 30))
Triangle(Point2D(0, 0), Point2D(1, 0), Point2D(1/2, sqrt(3)/6))
>>> Triangle(sas=(1, 45, 2))
Triangle(Point2D(0, 0), Point2D(2, 0), Point2D(sqrt(2)/2, sqrt(2)/2))


Attributes

property altitudes

The altitudes of the triangle.

An altitude of a triangle is a segment through a vertex, perpendicular to the opposite side, with length being the height of the vertex measured from the line containing the side.

Returns

altitudes : dict

The dictionary consists of keys which are vertices and values which are Segments.

Examples

>>> from sympy.geometry import Point, Triangle
>>> p1, p2, p3 = Point(0, 0), Point(1, 0), Point(0, 1)
>>> t = Triangle(p1, p2, p3)
>>> t.altitudes[p1]
Segment2D(Point2D(0, 0), Point2D(1/2, 1/2))

bisectors()[source]

The angle bisectors of the triangle.

An angle bisector of a triangle is a straight line through a vertex which cuts the corresponding angle in half.

Returns

bisectors : dict

Each key is a vertex (Point) and each value is the corresponding bisector (Segment).

Examples

>>> from sympy.geometry import Point, Triangle, Segment
>>> p1, p2, p3 = Point(0, 0), Point(1, 0), Point(0, 1)
>>> t = Triangle(p1, p2, p3)
>>> from sympy import sqrt
>>> t.bisectors()[p2] == Segment(Point(1, 0), Point(0, sqrt(2) - 1))
True

property circumcenter

The circumcenter of the triangle

The circumcenter is the center of the circumcircle.

Returns

circumcenter : Point

Examples

>>> from sympy.geometry import Point, Triangle
>>> p1, p2, p3 = Point(0, 0), Point(1, 0), Point(0, 1)
>>> t = Triangle(p1, p2, p3)
>>> t.circumcenter
Point2D(1/2, 1/2)

property circumcircle

The circle which passes through the three vertices of the triangle.

Returns

circumcircle : Circle

Examples

>>> from sympy.geometry import Point, Triangle
>>> p1, p2, p3 = Point(0, 0), Point(1, 0), Point(0, 1)
>>> t = Triangle(p1, p2, p3)
>>> t.circumcircle
Circle(Point2D(1/2, 1/2), sqrt(2)/2)

property circumradius

The radius of the circumcircle of the triangle.

Returns

circumradius : number of Basic instance

Examples

>>> from sympy import Symbol
>>> from sympy.geometry import Point, Triangle
>>> a = Symbol('a')
>>> p1, p2, p3 = Point(0, 0), Point(1, 0), Point(0, a)
>>> t = Triangle(p1, p2, p3)
sqrt(a**2/4 + 1/4)

property eulerline

The Euler line of the triangle.

The line which passes through circumcenter, centroid and orthocenter.

Returns

eulerline : Line (or Point for equilateral triangles in which case all

centers coincide)

Examples

>>> from sympy.geometry import Point, Triangle
>>> p1, p2, p3 = Point(0, 0), Point(1, 0), Point(0, 1)
>>> t = Triangle(p1, p2, p3)
>>> t.eulerline
Line2D(Point2D(0, 0), Point2D(1/2, 1/2))

property excenters

Excenters of the triangle.

An excenter is the center of a circle that is tangent to a side of the triangle and the extensions of the other two sides.

Returns

excenters : dict

Examples

The excenters are keyed to the side of the triangle to which their corresponding excircle is tangent: The center is keyed, e.g. the excenter of a circle touching side 0 is:

>>> from sympy.geometry import Point, Triangle
>>> p1, p2, p3 = Point(0, 0), Point(6, 0), Point(0, 2)
>>> t = Triangle(p1, p2, p3)
>>> t.excenters[t.sides[0]]
Point2D(12*sqrt(10), 2/3 + sqrt(10)/3)


References

R469

http://mathworld.wolfram.com/Excircles.html

property exradii

The radius of excircles of a triangle.

An excircle of the triangle is a circle lying outside the triangle, tangent to one of its sides and tangent to the extensions of the other two.

Returns

Examples

The exradius touches the side of the triangle to which it is keyed, e.g. the exradius touching side 2 is:

>>> from sympy.geometry import Point, Triangle, Segment2D, Point2D
>>> p1, p2, p3 = Point(0, 0), Point(6, 0), Point(0, 2)
>>> t = Triangle(p1, p2, p3)
-2 + sqrt(10)


References

property incenter

The center of the incircle.

The incircle is the circle which lies inside the triangle and touches all three sides.

Returns

incenter : Point

Examples

>>> from sympy.geometry import Point, Triangle
>>> p1, p2, p3 = Point(0, 0), Point(1, 0), Point(0, 1)
>>> t = Triangle(p1, p2, p3)
>>> t.incenter
Point2D(1 - sqrt(2)/2, 1 - sqrt(2)/2)

property incircle

The incircle of the triangle.

The incircle is the circle which lies inside the triangle and touches all three sides.

Returns

incircle : Circle

Examples

>>> from sympy.geometry import Point, Triangle
>>> p1, p2, p3 = Point(0, 0), Point(2, 0), Point(0, 2)
>>> t = Triangle(p1, p2, p3)
>>> t.incircle
Circle(Point2D(2 - sqrt(2), 2 - sqrt(2)), 2 - sqrt(2))

property inradius

Returns

inradius : number of Basic instance

Examples

>>> from sympy.geometry import Point, Triangle
>>> p1, p2, p3 = Point(0, 0), Point(4, 0), Point(0, 3)
>>> t = Triangle(p1, p2, p3)
1

is_equilateral()[source]

Are all the sides the same length?

Returns

is_equilateral : boolean

Examples

>>> from sympy.geometry import Triangle, Point
>>> t1 = Triangle(Point(0, 0), Point(4, 0), Point(4, 3))
>>> t1.is_equilateral()
False

>>> from sympy import sqrt
>>> t2 = Triangle(Point(0, 0), Point(10, 0), Point(5, 5*sqrt(3)))
>>> t2.is_equilateral()
True

is_isosceles()[source]

Are two or more of the sides the same length?

Returns

is_isosceles : boolean

Examples

>>> from sympy.geometry import Triangle, Point
>>> t1 = Triangle(Point(0, 0), Point(4, 0), Point(2, 4))
>>> t1.is_isosceles()
True

is_right()[source]

Is the triangle right-angled.

Returns

is_right : boolean

Examples

>>> from sympy.geometry import Triangle, Point
>>> t1 = Triangle(Point(0, 0), Point(4, 0), Point(4, 3))
>>> t1.is_right()
True

is_scalene()[source]

Are all the sides of the triangle of different lengths?

Returns

is_scalene : boolean

Examples

>>> from sympy.geometry import Triangle, Point
>>> t1 = Triangle(Point(0, 0), Point(4, 0), Point(1, 4))
>>> t1.is_scalene()
True

is_similar(t2)[source]

Is another triangle similar to this one.

Two triangles are similar if one can be uniformly scaled to the other.

Parameters

other: Triangle

Returns

is_similar : boolean

Examples

>>> from sympy.geometry import Triangle, Point
>>> t1 = Triangle(Point(0, 0), Point(4, 0), Point(4, 3))
>>> t2 = Triangle(Point(0, 0), Point(-4, 0), Point(-4, -3))
>>> t1.is_similar(t2)
True

>>> t2 = Triangle(Point(0, 0), Point(-4, 0), Point(-4, -4))
>>> t1.is_similar(t2)
False

property medial

The medial triangle of the triangle.

The triangle which is formed from the midpoints of the three sides.

Returns

medial : Triangle

Examples

>>> from sympy.geometry import Point, Triangle
>>> p1, p2, p3 = Point(0, 0), Point(1, 0), Point(0, 1)
>>> t = Triangle(p1, p2, p3)
>>> t.medial
Triangle(Point2D(1/2, 0), Point2D(1/2, 1/2), Point2D(0, 1/2))

property medians

The medians of the triangle.

A median of a triangle is a straight line through a vertex and the midpoint of the opposite side, and divides the triangle into two equal areas.

Returns

medians : dict

Each key is a vertex (Point) and each value is the median (Segment) at that point.

Examples

>>> from sympy.geometry import Point, Triangle
>>> p1, p2, p3 = Point(0, 0), Point(1, 0), Point(0, 1)
>>> t = Triangle(p1, p2, p3)
>>> t.medians[p1]
Segment2D(Point2D(0, 0), Point2D(1/2, 1/2))

property nine_point_circle

The nine-point circle of the triangle.

Nine-point circle is the circumcircle of the medial triangle, which passes through the feet of altitudes and the middle points of segments connecting the vertices and the orthocenter.

Returns

nine_point_circle : Circle

Examples

>>> from sympy.geometry import Point, Triangle
>>> p1, p2, p3 = Point(0, 0), Point(1, 0), Point(0, 1)
>>> t = Triangle(p1, p2, p3)
>>> t.nine_point_circle
Circle(Point2D(1/4, 1/4), sqrt(2)/4)

property orthocenter

The orthocenter of the triangle.

The orthocenter is the intersection of the altitudes of a triangle. It may lie inside, outside or on the triangle.

Returns

orthocenter : Point

Examples

>>> from sympy.geometry import Point, Triangle
>>> p1, p2, p3 = Point(0, 0), Point(1, 0), Point(0, 1)
>>> t = Triangle(p1, p2, p3)
>>> t.orthocenter
Point2D(0, 0)

property vertices

The triangle’s vertices

Returns

vertices : tuple

Each element in the tuple is a Point

Examples

>>> from sympy.geometry import Triangle, Point
>>> t = Triangle(Point(0, 0), Point(4, 0), Point(4, 3))
>>> t.vertices
(Point2D(0, 0), Point2D(4, 0), Point2D(4, 3))