Screen To WorldXY - Exact under tip of pointer

[D-W (Przemysław Doliwa)]

As the topic says, I’m looking for a direct, well-performing way to get the exact spot on WorldXY plane - going from there to an arbitrary plane should be fairly easy as long as we operate on xforms, though no matter how hard I would try, already mentioned methods in:

Transform Screen to World Coordinates

Get mouse position in active viewport + cplane coords

To transform a 2-D screen point to a 3-D world xy-plane point, you can do something like this: Rhino.Display.RhinoView view = doc.Views.ActiveView; Rhino.Geometry.Transform xform = view.ActiveViewport.GetTransform( Rhino.DocObjects.CoordinateSystem.Screen, Rhino.DocObjects.CoordinateSystem.World ); Rhino.Geometry.Point3d world_point = new Rhino.Geometry.Point3d( screen_point.X, screen_point.Y, 0.0 ); world_point.Transform(xform);

Converting between Screen and World coordinates

Hi @Matthieu_from_NAVINN, This is how I would compute the transform: Dim view as RhinoView = doc.Views.ActiveView If (Not IsNothing(view)) Then Dim xform as Transform = view.ActiveViewport.GetTransform(CoordinateSystem.Screen, CoordinateSystem.World) ' TODO: transform objects... End If – Dale

I got wrong results that do not match the left-bottom Rhino window indication of XYZ, according to the methods mentioned above, code called in derived MouseCallback OnMouseMove:

var vp = e.View.ActiveViewport;
var screenToWorld = vp.GetTransform(Rhino.DocObjects.CoordinateSystem.Screen, Rhino.DocObjects.CoordinateSystem.World);
var currentWorldPoint = screenToWorld * new Point3d(e.ViewportPoint.X, e.ViewportPoint.Y, 0);

RhinoApp.WriteLine(currentWorldPoint.ToString());

It should be an elegant way to get the spot, instead of that, I get variable Z results, like it would be some kind of intermediate xform to intermediate XYZ space, moving around origin results in:

I also noticed it depends on the zoom level (change of range of values), and it’s worth mentioning that it is related to perspective view, as X and Y in top view seem to be ok, though I get Z around ~10.5046

Additional example where it finds around origin (XY) values (black dot in vieport):

@dale Would you mind kicking in and leaving a hint on this?

[farouk.serragedine]

Hi @D-W ,
I’d go for Viewport.GetFrustumLine → intersect ray with Plane.WorldXY → point = ray.PointAt(t).
Very easy and straightforward,
Farouk

[michaelvollrath]

@farouk.serragedine

Viewport.GetFrustumLine → intersect ray with Plane.WorldXY → point = ray.PointAt(t).

^ This is what I’ve had with success as well

[D-W (Przemysław Doliwa)]

Hi guys! Thanks for your insight @farouk.serragedine & @michaelvollrath . That’s how I already handle it with perfect results in later delta calculations, though the idea was to use only matrices. Pure xform * xform - at least this should be the most performant way, fastest possible.