.. _ref_primitives:

Primitives
**********

The PyAnsys Geometry :class:`math <ansys.geometry.core.math>` subpackage consists
of primitive representations of basic geometric objects, such as a point, vector, and
matrix. To operate and manipulate physical quantities, this subpackage uses
`Pint <https://github.com/hgrecco/pint>`_, a third-party open source software
that other PyAnsys libraries also use. It also uses its :class:`shapes <ansys.geometry.core.shapes>`
subpackage to evaluate and represent geometric shapes (both curves and surfaces),
such as lines, circles, cones, spheres and torus.

This table shows PyAnsys Geometry names and base values for the physical quantities:

+----------------------------+---------+
| Name                       | value   |
+============================+=========+
| LENGTH_ACCURACY            | 1e-8    |
+----------------------------+---------+
| ANGLE_ACCURACY             | 1e-6    |
+----------------------------+---------+
| DEFAULT_UNITS.LENGTH       | meter   |
+----------------------------+---------+
| DEFAULT_UNITS.ANGLE        | radian  |
+----------------------------+---------+

To define accuracy and measurements, you use these PyAnsys Geometry classes:

* :class:`Accuracy() <ansys.geometry.core.misc.accuracy>`
* :class:`Measurements() <ansys.geometry.core.misc.measurements>`

Planes
------

The :class:`Plane() <ansys.geometry.core.math.plane>` class provides primitive representation
of a 2D plane in 3D space. It has an origin and a coordinate system.
Sketched shapes are always defined relative to a plane.
The default working plane is XY, which has ``(0,0)`` as its origin.

If you create a 2D object in the plane, PyAnsys Geometry converts it to the global coordinate system so that
the 2D feature executes as expected:

.. code:: python

    from ansys.geometry.core.math import Plane, Point3D, UnitVector3D

    origin = Point3D([42, 99, 13])
    plane = Plane(origin, UnitVector3D([1, 0, 0]), UnitVector3D([0, 1, 0]))