Added AreaNthSelector (#688)

* Added AreaNthSelector

Added AreaNthSelector that is useful for nested features selection. Especially to select one of coplanar nested wires for subsequent extrusion, cutting or filleting.

* LengthNthSelector

* Explicitly marked _NthSelector class and _NthSelector.key(..) method as abstract using standard abc package

* AreaNthSelector ignores "bad" Wires

AreaNthSelector.key raises ValueError if temporary face creation fails for a wire for any reason (non-planar, non-closed). That causes _NthSelector that it inherits to ignore such wires. Done so for consistency with RadiusNthSelector that ignores anything it can not get radius from.

Co-authored-by: Marcus Boyd <[email protected]>

Author: fedorkotov

cadquery/selectors.py

@@ -17,9 +17,19 @@
     License along with this library; If not, see <http://www.gnu.org/licenses/>
 """
 
+from abc import abstractmethod, ABC
 import math
 from .occ_impl.geom import Vector
-from .occ_impl.shapes import Shape, Edge, Face, Wire, geom_LUT_EDGE, geom_LUT_FACE
+from .occ_impl.shapes import (
+    Shape,
+    Edge,
+    Face,
+    Wire,
+    Shell,
+    Solid,
+    geom_LUT_EDGE,
+    geom_LUT_FACE,
+)
 from pyparsing import (
     Literal,
     Word,
@@ -294,7 +304,7 @@ def filter(self, objectList: Sequence[Shape]) -> List[Shape]:
         return r
 
 
-class _NthSelector(Selector):
+class _NthSelector(Selector, ABC):
     """
     An abstract class that provides the methods to select the Nth object/objects of an ordered list.
     """
@@ -324,6 +334,7 @@ def filter(self, objectlist: Sequence[Shape]) -> List[Shape]:
 
         return out
 
+    @abstractmethod
     def key(self, obj: Shape) -> float:
         """
         Return the key for ordering. Can raise a ValueError if obj can not be
@@ -454,6 +465,89 @@ def filter(self, objectlist: Sequence[Shape]) -> List[Shape]:
         return objectlist
 
 
+class LengthNthSelector(_NthSelector):
+    """
+    Select the object(s) with the Nth length
+
+    Applicability:
+        All Edge and Wire objects
+    """
+
+    def key(self, obj: Shape) -> float:
+        if isinstance(obj, (Edge, Wire)):
+            return obj.Length()
+        else:
+            raise ValueError(
+                f"LengthNthSelector supports only Edges and Wires, not {type(obj).__name__}"
+            )
+
+
+class AreaNthSelector(_NthSelector):
+    """
+    Selects the object(s) with Nth area
+
+    Applicability:
+        Faces, Shells, Solids - Shape.Area() is used to compute area
+        closed planar Wires - a temporary face is created to compute area
+
+    Will ignore non-planar or non-closed wires.
+    
+    Among other things can be used to select one of
+    the nested coplanar wires or faces.
+
+    For example to create a fillet on a shank:
+
+        result = (
+            cq.Workplane("XY")
+            .circle(5)
+            .extrude(2)
+            .circle(2)
+            .extrude(10)
+            .faces(">Z[-2]")
+            .wires(AreaNthSelector(0))
+            .fillet(2)
+        )
+
+    Or to create a lip on a case seam:
+
+        result = (
+            cq.Workplane("XY")
+            .rect(20, 20)
+            .extrude(10)
+            .edges("|Z or <Z")
+            .fillet(2)
+            .faces(">Z")
+            .shell(2)
+            .faces(">Z")
+            .wires(AreaNthSelector(-1))
+            .toPending()
+            .workplane()
+            .offset2D(-1)
+            .extrude(1)
+            .faces(">Z[-2]")
+            .wires(AreaNthSelector(0))
+            .toPending()
+            .workplane()
+            .cutBlind(2)
+        )
+    """
+
+    def key(self, obj: Shape) -> float:
+        if isinstance(obj, (Face, Shell, Solid)):
+            return obj.Area()
+        elif isinstance(obj, Wire):
+            try:
+                return Face.makeFromWires(obj).Area()
+            except Exception as ex:
+                raise ValueError(
+                    f"Can not compute area of the Wire: {ex}. AreaNthSelector supports only closed planar Wires."
+                )
+        else:
+            raise ValueError(
+                f"AreaNthSelector supports only Wires, Faces, Shells and Solids, not {type(obj).__name__}"
+            )
+
+
 class BinarySelector(Selector):
     """
     Base class for selectors that operates with two other

doc/apireference.rst

@@ -177,6 +177,8 @@ as a basis for futher operations.
         ParallelDirSelector
         DirectionSelector
         DirectionNthSelector
+		LengthNthSelector
+		AreaNthSelector
         RadiusNthSelector
         PerpendicularDirSelector
         TypeSelector

doc/classreference.rst

@@ -66,6 +66,8 @@ Selector Classes
     CenterNthSelector
     DirectionMinMaxSelector
     DirectionNthSelector
+    LengthNthSelector
+    AreaNthSelector
     BinarySelector
     AndSelector
     SumSelector

examples/Ex026_Case_Seam_Lip.py

@@ -0,0 +1,47 @@
+import cadquery as cq
+from cadquery.selectors import AreaNthSelector
+
+case_bottom = (
+    cq.Workplane("XY")
+    .rect(20, 20)
+    .extrude(10)  # solid 20x20x10 box
+    .edges("|Z or <Z")
+    .fillet(2)  # rounding all edges except 4 edges of the top face
+    .faces(">Z")
+    .shell(2)  # shell of thickness 2 with top face open
+    .faces(">Z")
+    .wires(AreaNthSelector(-1))  # selecting top outer wire
+    .toPending()
+    .workplane()
+    .offset2D(-1)  # creating centerline wire of case seam face
+    .extrude(1)  # covering the sell with temporary "lid"
+    .faces(">Z[-2]")
+    .wires(AreaNthSelector(0))  # selecting case crossection wire
+    .toPending()
+    .workplane()
+    .cutBlind(2)  # cutting through the "lid" leaving a lip on case seam surface
+)
+
+# similar process repeated for the top part
+# but instead of "growing" an inner lip
+# material is removed inside case seam centerline
+# to create an outer lip
+case_top = (
+    cq.Workplane("XY")
+    .move(25)
+    .rect(20, 20)
+    .extrude(5)
+    .edges("|Z or >Z")
+    .fillet(2)
+    .faces("<Z")
+    .shell(2)
+    .faces("<Z")
+    .wires(AreaNthSelector(-1))
+    .toPending()
+    .workplane()
+    .offset2D(-1)
+    .cutBlind(-1)
+)
+
+show_object(case_bottom)
+show_object(case_top, options={"alpha": 0.5})

tests/__init__.py

@@ -47,9 +47,9 @@ def toTuple(v):
 
 
 class BaseTest(unittest.TestCase):
-    def assertTupleAlmostEquals(self, expected, actual, places):
+    def assertTupleAlmostEquals(self, expected, actual, places, msg=None):
         for i, j in zip(actual, expected):
-            self.assertAlmostEqual(i, j, places)
+            self.assertAlmostEqual(i, j, places, msg=msg)
 
 
 __all__ = [