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FS#2620No intersections returned for an RSpline (fitPoints) and an RCircle

Type
Bug
Status
Assigned
Category
ECMAScript
Severity
Low
Priority
Low
Reported version
3.31.2
Operating system
Windows 7
Reported
2024-12-16 by CVH
Votes
1

Andrew,

Related to this Forum topic
(ArcTPR.js: Offsets to an ellipse are fit-point splines)

The array of intersections of a fit-point spline and a circle is always empty.

The method is broken ...
OR
The method is not implemented at all without mentioning it ...!?
(Already failing with QCAD 3.27.6.0)

Workaround 1:
Quote: If we trim or cut up a fit-Point spline the result(s) is/are (a) control-point spline(s).
If any, the intersections between these splines and a circle are valid.
Downside:
If the circle crosses the cutting point (or the start=end point when closed) then
two identical intersections are included.

Workaround 2: Approximate the fit-point spline with a polyline (Explode).
Expected are approximate intersections.
Unaware if that is the method used for intersections internally.

Below a simple script that can be run with XC:
-> No intersections as fit-point spline
-> 4 intersections as control-Point spline segments (Workaround 1)

// Example points to fit:
var fitpoints = [new RVector(0, 9),
                new RVector(7, 0),
                new RVector(0, -9),
                new RVector(-7, 0)];

// Create a spline shape:
var spline = new RSpline();
spline.setFitPoints(fitpoints);
spline.setPeriodic(true);
// Create a circle shape:
var circle = new RCircle(RVector.nullVector, 8.0);

// Get intersections of spline and circle, expecting 4:
var ips1 = spline.getIntersectionPoints(circle, false);
// Report the number of intersections on the Command History:
EAction.handleUserInfo("As fit-point spline: %1 intersections (of 4)".arg(ips1.length));

// Cut up the spline in two parts -> Control-Point spline
var cutPoint = spline.getTMin() + (spline.getTDelta()/2.0);    // fitPoint (0, -9)
var splines = spline.splitAtParams([cutPoint]);

// Get intersections of both spline segments and circle:
var ips2 = splines[0].getIntersectionPoints(circle, false);
ips2 = ips2.concat(splines[1].getIntersectionPoints(circle, false));
// Report the number of intersections on the Command History:
EAction.handleUserInfo("As control-point splines: %1 intersections (of 4)".arg(ips2.length));

Regards,
CVH

Comments (2)

CVH 2025-01-05

Found another solution ...

If we swap the RShapes in the above code then all is OK.

// Replace:
var ips1 = spline.getIntersectionPoints(circle, false);
// With:
var ips1 = circle.getIntersectionPoints(spline, false);

I assumed that the order didn't matter.
RShape::getIntersectionPoints(shape1, shape2, limited, same, force)
Returns practically the same thing as it dynamically swaps both shapes:
Circle vs Spline => return getIntersectionPointsCS(*circle1, *spline2, limited);
Spline vs Circle => return getIntersectionPointsCS(*circle2, *spline1, limited);

However, this is no solution for ArcTPR.js
Swapping the order of shapes in the original code:

// Replace:
            // find potential centers for arc:
            var ips = parallel.getIntersectionPoints(circle, false);
// With:
            // find potential centers for arc:
            var ips = circle.getIntersectionPoints(parallel, false);

Will throw an error: RShape: Argument 0 is not of type RShape*.
Argument 0 or the spline is indeed a QSharedPointer. (Reference)

Can it be that it must be 2 RShape's or at least an RShape as argument?

Regards,
CVH

CVH 2025-01-07

More on the subject in this forum topic.
With examples, visualization, recent code and so on.

Regards,
CVH