By on Monday, April 13, 2020 (2808 views)

Circles and Ellipse

A circle in the XY plane can be created using the Circle declaration. The circle's origin is at the center and is defined by simply setting the radius. Similarly an Ellipse is defined by specifying a major_radius and a minor_radius. The ellipse can be rotated by setting the rotation in radians.

# Created in DeclaraCAD
from declaracad.occ.api import *

enamldef Assembly(Part):        
    Circle:
        color = 'red'
        radius = 5

    Ellipse:
        color = 'blue'
        major_radius = 5
        minor_radius = 3

    # For reference    
    Line: xaxis:
        color = 'black'
        direction = (1, 0)
    Line: yaxis:
        color = 'black'
        direction = (0, 1)

Circle and Ellipse

To move it into another plane use a Transform or set the direction attribute.

Arcs

An Arc can be defined by several different sets of attributes:

  • The position, radius and two angles alpha1, and alpha2 (in radians) (See arc1)
  • A radius and two points it must pass through (See arc2)
  • Three points (See arc3)
  • A start point, a start direction, and an end point

Note: When creating an arc using a position, radius, and two points make sure they are all on a single plane.

# Created in DeclaraCAD
from math import pi
from declaracad.occ.api import *

enamldef Assembly(Part):        
    Arc: arc1:
        color = 'red'
        radius = 3
        alpha1 = 0
        alpha2 = pi/2

    Arc: arc2:
        color = 'blue'
        radius = 3
        points = [(0, 3), (3, 0)]

    Arc: arc3:
        color = 'lime'
        points = [arc2.start, (0, 0), arc2.end]

    # For reference    
    Line: xaxis:
        color = 'black'
        direction = (1, 0)
    Line: yaxis:
        color = 'black'
        direction = (0, 1)

Arcs

The start and end point of an Arc can be retrieved using the start and end attributes which is very useful for building wires as we'll see later.

If the second entry in the points list is a direction it is interpreted as the start tangent and the other values are computed.

# Created in DeclaraCAD
from declaracad.occ.api import *
from declaracad.parts.display import Axis

enamldef Assembly(Part):
    Axis:
        pass
    Polyline: up:
        points = [
            (0, 0),
            (1, 3),
        ]
    Arc:
        color = 'orange'
        points = [
            *up.topology.end_tangent,
           down.topology.start_point
        ]
    Polyline: down:
        color = 'blue'
        points = [
            (3, 2),
            (3, 0),
        ]

Arc start tangent