Intersection and Trim

Many of the examples so far have focused on the construction of higher dimensional geometry from lower dimensional objects. Intersection methods allow this higher dimensional geometry to generate lower dimensional objects, while the trim and select trim commands allow script to heavily modify geometric forms after they’ve been created.

The Intersect method is defined on all pieces of geometry in Dynamo, meaning that in theory any piece of geometry can be intersected with any other piece of geometry. Naturally some intersections are meaningless, such as intersections involving Points, as the resulting object will always be the input Point itself. The other possible combinations of intersections between objects are outlined in the following chart. The following chart outlines the result of various intersection operations:

Intersect

With:	Surface	Curve	Plane	Solid
Surface	Curve	Point	Point, Curve	Surface
Curve	Point	Point	Point	Curve
Plane	Curve	Point	Curve	Curve
Solid	Surface	Curve	Curve	Solid

The following very simple example demonstrates the intersection of a plane with a NurbsSurface. The intersection generates a NurbsCurve array, which can be used like any other NurbsCurve.

// python_points_5 is a set of Points generated with
// a Python script found in Chapter 12, Section 10

surf = NurbsSurface.ByPoints(python_points_5, 3, 3);

WCS = CoordinateSystem.Identity();

pl = Plane.ByOriginNormal(WCS.Origin.Translate(0, 0,
    0.5), WCS.ZAxis);

// intersect surface, generating three closed curves
crvs = surf.Intersect(pl);

crvs_moved = crvs.Translate(0, 0, 10);

The Trim method is very similar to the Intersect method, in that it is defined for almost every piece of geometry. However, there are far more limitations on Trim than on Intersect.

Trim

	Using: Point	Curve	Plane	Surface	Solid
On: Curve	Yes	No	No	No	No
Polygon	-	No	Yes	No	No
Surface	-	Yes	Yes	Yes	Yes
Solid	-	-	Yes	Yes	Yes

Something to note about Trim methods is the requirement of a “select” point, a point which determines which geometry to discard, and which pieces to keep. Dynamo finds and discards the trimmed geometry closest to the select point.

// python_points_5 is a set of Points generated with
// a Python script found in Chapter 12, Section 10

surf = NurbsSurface.ByPoints(python_points_5, 3, 3);

tool_pts = Point.ByCoordinates((-10..20..10)<1>,
    (-10..20..10)<2>, 1);

tool = NurbsSurface.ByPoints(tool_pts);

pick_point = Point.ByCoordinates(8, 1, 3);

result = surf.Trim(tool, pick_point);