sketch returns another sketch instead of referencePlane

[metd01567]

I'm trying to get the normal to a sketch, via the reference plane's geometry.  But for the "Slots" sketch in the attached example, the referencePlane is a "Sketch" object.  If I redefine the Slots sketch plane to the root XY plane, I get a "ConstructionPlane" as expected.

Here's the offending code:

import adsk.core, adsk.fusion, traceback


def run(context):
    try:
        app = adsk.core.Application.get()
        ui = app.userInterface
        product = app.activeProduct
        design = adsk.fusion.Design.cast(product)
        comp = design.rootComponent

        refSketch = comp.sketches.itemByName("Slots")

        ui.messageBox("sketch plane is a: " + refSketch.referencePlane.classType())

        rotAxis = refSketch.referencePlane.geometry.normal

    except:
        if ui:
            ui.messageBox('Failed:\n{}'.format(traceback.format_exc()))

[goyals · Accepted solution]

To create a sketch, we can use another sketch as referencePlane for it. If you query referencePlane again on returned sketch, you will get the construction plane of it.

[metd01567]

I added:

        
        ui.messageBox("sketch's sketch plane is a: " + refSketch.referencePlane.referencePlane.classType())

but that returned "Profile".

[metd01567]

Of course, a sketch's reference plane can be a profile too.  Over time I've become more careful about sketch interdependencies, but this started as one of my first projects.  I don't doubt that I had a sketch referencing a sketch which then referenced a profile (which then belonged in a sketch).

So now I'd like to change my question to: "how can a script reliably determine a sketch's normal?".  Technically you've solved my original problem, should I start a new topic or do we keep going here?

This points to a common problem in the API documentation. In general when a property or method returns multiple types, we've got to rely on the Description text to psych out the possibilities.   The Description for Sketch.referencePlane: says "construction plane or planar face the sketch is associated to".  I figured out ConstructionPlane, but what are all possible types of "planar face"?

Even if I had a complete list of referencePlane types, the ones I know of don't have a common method or property to determine the normal.  The code to sift through them would be messy.  And brittle, API changes could break it.  Should I request adding a "normal" property to Sketch, completing the "xDirection" and "yDirection"?  In theory I should be able to derive normal from x/y direction using the right hand rule.  But I'd have to pull out my textbooks to do it. 

[BrianEkins · Accepted solution]

The easiest way is to get it directly from the sketch. Unfortunately it's not directly exposed but using other information that is exposed it's easy to compute. Something like:

normal = sk.xDirection.crossProduct(sk.yDirection)

[metd01567]

Thanks. I did a general search for "cross product" but of course it's found by "crossproduct".   I wasn't expecting it  in Vector3D, but it makes sense.  You caught me just in time, before I tried to cook something up myself.

I changed my rotational axis assignment to:

    rotAxis = rotSketch.xDirection.crossProduct(rotSketch.yDirection)

and that did the trick.