Improved documentation for `regridding.geometry.two_line_segment_inte…

…rsection_parameters()`.

regridding/geometry.py

@@ -202,7 +202,27 @@ def two_line_segment_intersection_parameters(
  Computes the parameters
  (:math:`\text{sdet}`, :math:`\text{tdet}`, and :math:`\text{det}`)
  associated with the intersection of two 2D line segments,
- :math:`p` and :math:`q`, as described in :footcite:t:`GraphicsGemsIII`.
+ :math:`p` and :math:`q`.
+
+ This function uses the method described in :footcite:t:`GraphicsGemsIII`.
+ :math:`\text{sdet}`, :math:`\text{tdet}`, and :math:`\text{det}` are expected
+ to be used to compute the quantities
+
+ .. math::
+
+ s &= \text{sdet} / \text{det}
+ t &= \text{tdet} / \text{det},
+
+ which can be used to compute the intersection :math:`(x, y)` using the
+ parametric equations of the lines:
+
+ .. math::
+
+ x = (1 - s) * x_{\text{q1}} + s * x_{\text{q2}} = (1 - t) * x_{\text{p1}} + t * x_{\text{p2}}
+ y = (1 - s) * y_{\text{q1}} + s * y_{\text{q2}} = (1 - t) * y_{\text{p1}} + t * y_{\text{p2}}.
+
+ The quantities :math:`s` and :math:`t` are not computed directly
+ because doing so leads to a loss of precision.
 
  Parameters
  ----------