Project 3D part to plane

Simulate the API from Build123d `project_to_viewpoint`: Given a 3D
vector representing the camera position pointing at the origin
`(0,0,0)`, render all visible edges/arcs/splines representing the outline
of the 3D part projected to the camera.

Also render all hidden edges/arcs/splines.

Provide and example script `tests/test_projection.py` where a generic
part (A bracket with rounded corners and a countersunk hole) is
projected to top view, side view, front view, and orthogonal view, and
then exported to DXF 2D drawings.

Reference: https://build123d.readthedocs.io/en/latest/tech_drawing_tutorial.html

Author: antonysigma

cadquery/occ_impl/exporters/dxf.py

@@ -157,6 +157,7 @@ def add_shape(self, shape: Union[WorkplaneLike, Shape], layer: str = "") -> Self
             plane = shape.plane
             shape_ = compound(*shape.__iter__()).transformShape(plane.fG)
         else:
+            plane = Plane((0,0,0))
             shape_ = shape
 
         general_attributes = {}

cadquery/occ_impl/exporters/svg.py

@@ -1,13 +1,10 @@
 import io as StringIO
 
-from ..shapes import Shape, Compound, TOLERANCE
+from ..shapes import Shape, Compound, Edge
 from ..geom import BoundBox
+from ..projection import projectToViewpoint
 
 
-from OCP.gp import gp_Ax2, gp_Pnt, gp_Dir
-from OCP.BRepLib import BRepLib
-from OCP.HLRBRep import HLRBRep_Algo, HLRBRep_HLRToShape
-from OCP.HLRAlgo import HLRAlgo_Projector
 from OCP.GCPnts import GCPnts_QuasiUniformDeflection
 
 DISCRETIZATION_TOLERANCE = 1e-3
@@ -106,26 +103,24 @@ def makeSVGedge(e):
     return cs.getvalue()
 
 
-def getPaths(visibleShapes, hiddenShapes):
+def getPaths(visibleEdges: list[Edge], hiddenEdges: list[Edge]) -> tuple[list[str], list[str]]:
     """
     Collects the visible and hidden edges from the CadQuery object.
     """
 
     hiddenPaths = []
     visiblePaths = []
 
-    for s in visibleShapes:
-        for e in s.Edges():
-            visiblePaths.append(makeSVGedge(e))
+    for e in visibleEdges:
+        visiblePaths.append(makeSVGedge(e))
 
-    for s in hiddenShapes:
-        for e in s.Edges():
-            hiddenPaths.append(makeSVGedge(e))
+    for e in hiddenEdges:
+        hiddenPaths.append(makeSVGedge(e))
 
     return (hiddenPaths, visiblePaths)
 
 
-def getSVG(shape, opts=None):
+def getSVG(shape: Shape, opts=None):
     """
     Export a shape to SVG text.
 
@@ -171,10 +166,10 @@ def getSVG(shape, opts=None):
 
     # Handle the case where the height or width are None
     width = d["width"]
-    if width != None:
+    if width is not None:
         width = float(d["width"])
     height = d["height"]
-    if d["height"] != None:
+    if d["height"] is not None:
         height = float(d["height"])
     marginLeft = float(d["marginLeft"])
     marginTop = float(d["marginTop"])
@@ -184,66 +179,18 @@ def getSVG(shape, opts=None):
     strokeColor = tuple(d["strokeColor"])
     hiddenColor = tuple(d["hiddenColor"])
     showHidden = bool(d["showHidden"])
-    focus = float(d["focus"]) if d.get("focus") else None
+    focus = float(d["focus"]) if d.get("focus") is not None else None
 
-    hlr = HLRBRep_Algo()
-    hlr.Add(shape.wrapped)
-
-    coordinate_system = gp_Ax2(gp_Pnt(), gp_Dir(*projectionDir))
-
-    if focus is not None:
-        projector = HLRAlgo_Projector(coordinate_system, focus)
-    else:
-        projector = HLRAlgo_Projector(coordinate_system)
-
-    hlr.Projector(projector)
-    hlr.Update()
-    hlr.Hide()
-
-    hlr_shapes = HLRBRep_HLRToShape(hlr)
-
-    visible = []
-
-    visible_sharp_edges = hlr_shapes.VCompound()
-    if not visible_sharp_edges.IsNull():
-        visible.append(visible_sharp_edges)
-
-    visible_smooth_edges = hlr_shapes.Rg1LineVCompound()
-    if not visible_smooth_edges.IsNull():
-        visible.append(visible_smooth_edges)
-
-    visible_contour_edges = hlr_shapes.OutLineVCompound()
-    if not visible_contour_edges.IsNull():
-        visible.append(visible_contour_edges)
-
-    hidden = []
-
-    hidden_sharp_edges = hlr_shapes.HCompound()
-    if not hidden_sharp_edges.IsNull():
-        hidden.append(hidden_sharp_edges)
-
-    hidden_contour_edges = hlr_shapes.OutLineHCompound()
-    if not hidden_contour_edges.IsNull():
-        hidden.append(hidden_contour_edges)
-
-    # Fix the underlying geometry - otherwise we will get segfaults
-    for el in visible:
-        BRepLib.BuildCurves3d_s(el, TOLERANCE)
-    for el in hidden:
-        BRepLib.BuildCurves3d_s(el, TOLERANCE)
-
-    # convert to native CQ objects
-    visible = list(map(Shape, visible))
-    hidden = list(map(Shape, hidden))
-    (hiddenPaths, visiblePaths) = getPaths(visible, hidden)
+    visibleEdges, hiddenEdges = projectToViewpoint(shape, projectionDir, focus)
+    (hiddenPaths, visiblePaths) = getPaths(visibleEdges, hiddenEdges)
 
     # get bounding box -- these are all in 2D space
-    bb = Compound.makeCompound(hidden + visible).BoundingBox()
+    bb = Compound.makeCompound(hiddenEdges + visibleEdges).BoundingBox()
 
     # Determine whether the user wants to fit the drawing to the bounding box
-    if width == None or height == None:
+    if width is None or height is None:
         # Fit image to specified width (or height)
-        if width == None:
+        if width is None:
             width = (height - (2.0 * marginTop)) * (
                 bb.xlen / bb.ylen
             ) + 2.0 * marginLeft

cadquery/occ_impl/projection.py

@@ -0,0 +1,72 @@
+from typing import Optional
+
+from OCP.BRepLib import BRepLib
+from OCP.gp import gp_Ax2, gp_Dir, gp_Pnt
+from OCP.HLRAlgo import HLRAlgo_Projector
+from OCP.HLRBRep import HLRBRep_Algo, HLRBRep_HLRToShape
+
+from .shapes import TOLERANCE, Edge, Shape
+
+DISCRETIZATION_TOLERANCE = 1e-3
+
+
+def projectToViewpoint(
+    shape,
+    projectionDir: tuple[float, float, float],
+    focus: Optional[float] = None,
+) -> tuple[list[Edge], list[Edge]]:
+    hlr = HLRBRep_Algo()
+    hlr.Add(shape.wrapped)
+
+    coordinate_system = gp_Ax2(gp_Pnt(), gp_Dir(*projectionDir))
+
+    if focus is not None:
+        projector = HLRAlgo_Projector(coordinate_system, focus)
+    else:
+        projector = HLRAlgo_Projector(coordinate_system)
+
+    hlr.Projector(projector)
+    hlr.Update()
+    hlr.Hide()
+
+    hlr_shapes = HLRBRep_HLRToShape(hlr)
+
+    visible = []
+
+    visible_sharp_edges = hlr_shapes.VCompound()
+    if not visible_sharp_edges.IsNull():
+        visible.append(visible_sharp_edges)
+
+    visible_smooth_edges = hlr_shapes.Rg1LineVCompound()
+    if not visible_smooth_edges.IsNull():
+        visible.append(visible_smooth_edges)
+
+    visible_contour_edges = hlr_shapes.OutLineVCompound()
+    if not visible_contour_edges.IsNull():
+        visible.append(visible_contour_edges)
+
+    hidden = []
+
+    hidden_sharp_edges = hlr_shapes.HCompound()
+    if not hidden_sharp_edges.IsNull():
+        hidden.append(hidden_sharp_edges)
+
+    hidden_contour_edges = hlr_shapes.OutLineHCompound()
+    if not hidden_contour_edges.IsNull():
+        hidden.append(hidden_contour_edges)
+
+    # Fix the underlying geometry - otherwise we will get segfaults
+    for el in visible:
+        BRepLib.BuildCurves3d_s(el, TOLERANCE)
+    for el in hidden:
+        BRepLib.BuildCurves3d_s(el, TOLERANCE)
+
+    # convert to native CQ objects
+    visible = [Shape.cast(s) for s in visible]  # s is a TopoDS_Shape (Compound)
+    hidden = [Shape.cast(s) for s in hidden]
+
+    # Extract edges
+    visible_edges = [e for c in visible for e in c.Edges()]
+    hidden_edges = [e for c in hidden for e in c.Edges()]
+
+    return visible_edges, hidden_edges

tests/test_projection.py

@@ -0,0 +1,61 @@
+import cadquery as cq
+from cadquery.occ_impl.projection import projectToViewpoint
+from cadquery.occ_impl.exporters.svg import exportSVG
+from cadquery.occ_impl.shapes import Compound
+from cadquery import Workplane
+
+viewpoint = {
+    "top": (0, 0, 1),
+    "left": (1, 0, 0),
+    "front": (0, 1, 0),
+    "ortho": (1, 1, 1),
+}
+
+
+def exportDXF3rdAngleProjection(my_part: Workplane, prefix: str) -> None:
+    for name, direction in viewpoint.items():
+        visible_edges, hidden_edges = projectToViewpoint(my_part.val(), direction)
+        cq.exporters.exportDXF(
+            Compound.makeCompound(visible_edges),
+            f"{prefix}{name}.dxf",
+            doc_units=6,
+        )
+
+
+def exportSVG3rdAngleProjection(my_part, prefix: str) -> None:
+    for name, direction in viewpoint.items():
+        exportSVG(
+            my_part,
+            f"{prefix}{name}.svg",
+            opts={
+                "projectionDir": direction,
+            },
+        )
+
+
+if __name__ == "__main__":
+    # Build the part
+    width = 10
+    depth = 10
+    height = 10
+
+    # !!! Test projection of fillets to arc segments in DXF. !!!
+    baseplate = (
+        cq.Workplane("XY")  #
+        .box(width, depth, height)
+        .edges("|Z")
+        .fillet(2.0)
+    )
+
+    hole_dia = 3.0
+
+    # !!! Test projection of countersunk to arc segments in DXF. !!!
+    drilled = (
+        baseplate.faces(">Z")  #
+        .workplane()
+        .cskHole(hole_dia, hole_dia * 2, 82.0)
+    )
+
+    # Expected DXF output to be identical to SVG output
+    exportSVG3rdAngleProjection(drilled, "")
+    exportDXF3rdAngleProjection(drilled, "")