Converting sketches

A part often starts as a quick sketch and needs dimensions later, or it comes from a solid whose face is the starting point. copy=True makes a new sketch from another one or from a face:

• px.Sketch(quick, copy=True) turns a quick sketch into a constraint sketch;

• px.QuickSketch(sketch, copy=True) turns a constraint sketch into a quick sketch;

• px.QuickSketch(face, copy=True) takes over the outline of a face of a solid.

Without copy=True, the same calls give an empty sketch on the plane of the object.

import math
import netgen.occ as occ
import planex as px

From a quick sketch to a constraint sketch

The example is a lever 40 long between the centers of its round ends, 12 wide, with a bore of 6 in its right end. It is drawn as a quick sketch, with each round end continuing the line before it (Figure 1a).

quick = px.QuickSketch((0, -6))
quick.Line(40, id="lower").Arc(6, 180, id="end").Line(40, id="upper").Arc(6, 180, id="back")
quick.Circle(40, 0, 3, id="bore");

px.Sketch(quick, copy=True) copies the geometry with its ids, names, construction elements and the pen, but no constraints, because a quick sketch has none. With auto_constraint=True, it adds the constraints the drawing shows: an arc tangent where a chain runs on smoothly, and coincident points where separate elements meet. Here, it finds the four tangent joints and the closing point of the outline:

lever = px.Sketch(quick, copy=True, auto_constraint=True)
print(lever.status, lever.dof, {kind: list(ids) for kind, ids in lever.constraints.items()})

under 7 {'Tangent': ['Tangent.1', 'Tangent.2', 'Tangent.3', 'Tangent.4'], 'Coincident': ['Coincident.1']}

The rest are the dimensions of the part: the length and the radius of the ends, the bore, and its place in the right end. With them, the lever is fully constrained (Figure 1b).

lever.Constrain("lower.start", px.Fix)
lever.Constrain("lower", px.Horizontal)
lever.Constrain("lower", px.Distance, 40, id="L")
lever.Constrain("end", px.Radius, 6, id="R")
lever.Constrain("back", "end", px.Equal)
lever.Constrain("bore", px.Radius, 3, id="r")
lever.Constrain("bore.center", "end.center", px.Coincident)
print(lever.status, lever.dof)

full 0

(a) (a) The quick sketch

(b) (b) Converted and dimensioned

Figure 1: A lever drawn quickly, then converted into a constraint sketch

A new length is now one dimension. The lever 60 long has the area of a slot of 60 × 12 less the bore, 60 · 12 + π 6² − π 3²:

lever["L"] = 60
lever.Update()
print("area", lever.Face().mass, "exact", 60 * 12 + math.pi * 6**2 - math.pi * 3**2)

area 804.8230016469245 exact 804.8230016469244

Rectangles, polygons, slots, fillets, offsets, patterns and mirrors of the quick sketch arrive as their lines and arcs, without the constraints that would keep them a rectangle or a slot.

From a constraint sketch to a quick sketch

px.QuickSketch(sketch, copy=True) keeps the solved geometry and drops the constraints, dimensions and expressions. A quick sketch is faster to draw into, for example for many copies in a study:

frozen = px.QuickSketch(lever, copy=True)
print(type(frozen).__name__, "area", frozen.Face().mass)

QuickSketch area 804.8230016469245

From the face of a solid

px.QuickSketch(face, copy=True) with a planar OpenCASCADE face gives a sketch on the face’s plane with the face’s outline in it, as normal geometry. The example is the top of a block 30 × 20 × 10 with a bore of 8. The sketch has the block’s outline and the circle of the bore, and more elements can be drawn on top of them.

block = occ.Box(occ.Pnt(0, 0, 0), occ.Pnt(30, 20, 10)) - occ.Cylinder(occ.Pnt(15, 10, 0), occ.Z, 4, 10)
top = block.faces.Max(occ.Z)
on_top = px.QuickSketch(top, copy=True)
print("area", on_top.Face().mass, "exact", 30 * 20 - math.pi * 4**2)

area 549.7345175425633 exact 549.7345175425633

A list of OpenCASCADE wires works the same way, and px.Sketch(wires, copy=True) gives a constraint sketch from them. See Placing a sketch for sketches on the faces of solids and Pad and Pocket for turning a sketch into a solid.