// Obtain workspace beforehand and open for writing.
Workspace workspace = ...
workspace.Open(false, false);
// Start position of the auxiliary line.
TransformProperty<LengthProperty> startPosition = new TransformProperty<LengthProperty>
(
new LengthProperty(10, Unit.Millimeter),
new LengthProperty(12, Unit.Millimeter),
new LengthProperty(-5, Unit.Millimeter)
);
// End position of the auxiliary line.
TransformProperty<LengthProperty> endPosition = new TransformProperty<LengthProperty>
(
new LengthProperty(50, Unit.Millimeter),
new LengthProperty(0, Unit.Millimeter),
new LengthProperty(-10, Unit.Millimeter)
);
// Place auxiliary line.
BaseOccurrence auxPlane = workspace.PlaceAuxiliaryLine(startPosition, endPosition);