Updates segment_vertices function

Renamed PI and CC to TI and NI
Fixes handling of units (now works correctly with US and SI units)
Changed tests to use US feet units
Fixed documentation

src/ifcopenshell-python/ifcopenshell/api/alignment/segment_vertices.py

@@ -23,32 +23,35 @@ import ifcopenshell
 import ifcopenshell.util.unit
 from ifcopenshell import entity_instance, ifcopenshell_wrapper
 
-def _intersect_lines(p1,d1,p2,d2):
-    x1,y1 = p1
-    dx1,dy1 = d1
-    x2,y2 = p2
-    dx2,dy2 = d2
-    
-    det = dx1*dy2 - dy1*dx2
+
+def _intersect_lines(p1, d1, p2, d2):
+    x1, y1 = p1
+    dx1, dy1 = d1
+    x2, y2 = p2
+    dx2, dy2 = d2
+
+    det = dx1 * dy2 - dy1 * dx2
     if abs(det) < 1e-12:
-        return None # lines are parallel
-    
-    t = ((x2 - x1) * dy2 - (y2 - y1) * dx2)/det
+        return None  # lines are parallel
 
-    x = x1 + t*dx1
-    y = y1 + t*dy1
+    t = ((x2 - x1) * dy2 - (y2 - y1) * dx2) / det
 
-    return (x,y)
+    x = x1 + t * dx1
+    y = y1 + t * dy1
+
+    return (x, y)
 
 
-def segment_vertices(file: ifcopenshell.file, curve_segment: entity_instance):
+def segment_vertices(curve_segment: entity_instance):
     """
-    Genererates segment vertices. Segment vertices are the points where the tangents
-    at the start and end of the segment intersect (the PI point) and where lines
-    perpendicular to the start and end of the segment intersect (CC).
+    Generates segment vertices. Segment vertices are at the start and end as well as the points where the tangents
+    at the start and end of the segment intersect (the TI point) and where lines
+    normal (perpendicular) to the start and end of the segment intersect (NI).
+
+    TI and NI are None if intersection points do not exist, such as in the case of a line.
 
     :param curve_segment: A curve segment
-    :return: tuples for Start, End, PI, CC
+    :return: tuples for Start, End, TI, NI
     """
     supported_segment_types = ["IFCCURVESEGMENT"]
     segment_type = curve_segment.is_a().upper()
@@ -56,8 +59,6 @@ def segment_vertices(file: ifcopenshell.file, curve_segment: entity_instance):
         raise NotImplementedError(
             f"Expected entity type to be one of {[_ for _ in supported_segment_types]}, got '{segment_type}"
         )
-    
-    unit_scale = ifcopenshell.util.unit.calculate_unit_scale(file)
 
     settings = ifcopenshell.geom.settings()
     segment_fn = ifcopenshell_wrapper.map_shape(settings, curve_segment.wrapped_data)
@@ -65,26 +66,25 @@ def segment_vertices(file: ifcopenshell.file, curve_segment: entity_instance):
 
     s = segment_evaluator.evaluate(segment_fn.start())
     start = np.array(s)
-    sx = float(start[0, 3]) / unit_scale
-    sy = float(start[1, 3]) / unit_scale
+    sx = float(start[0, 3])
+    sy = float(start[1, 3])
     sdx = float(start[0, 0])
-    sdy = float(start[1, 0])    
+    sdy = float(start[1, 0])
 
     e = segment_evaluator.evaluate(segment_fn.end())
     end = np.array(e)
-    unit_scale = ifcopenshell.util.unit.calculate_unit_scale(file)
-    ex = float(end[0, 3]) / unit_scale
-    ey = float(end[1, 3]) / unit_scale
+    ex = float(end[0, 3])
+    ey = float(end[1, 3])
     edx = float(end[0, 0])
     edy = float(end[1, 0])
 
-    pi = _intersect_lines((sx,sy),(sdx,sdy),(ex,ey),(edx,edy))
+    ti = _intersect_lines((sx, sy), (sdx, sdy), (ex, ey), (edx, edy))  # tangent intersection
 
     sdx = float(start[0, 1])
-    sdy = float(start[1, 1])    
+    sdy = float(start[1, 1])
     edx = float(end[0, 1])
     edy = float(end[1, 1])
 
-    cc = _intersect_lines((sx,sy),(sdx,sdy),(ex,ey),(edx,edy))
+    ni = _intersect_lines((sx, sy), (sdx, sdy), (ex, ey), (edx, edy))  # normal intersection
 
-    return (sx,sy), (ex,ey), pi, cc
+    return (sx, sy), (ex, ey), ti, ni