topic Re: UCS 3points in .NET Forum

UCS 3points

Anonymous — Tue, 30 Oct 2012 12:26:36 GMT

Hi,

I'm trying to place a UCS based on 3 points

- the origin of the UCS (PTOrigin)

- the x-direction (PTX)

- the y-direction (PTY)

The thing is that the angle between the vectorX (from origin to PTX) and vectorY (from origin to PTY) is not always 90°. Currently a create a new UCS in the UCSTable change the origin of the record to PTOrigin. Then I create a 3D vector from PTOrigin to PTX and then I'm stuck. I 'm unable to create a vector perpendicular to the vectorX which goes through PTY

Can anyone help me creating the Y-vector or are there other solutions for this?

thanks

Filip

Re: UCS 3points

Balaji_Ram — Mon, 05 Nov 2012 05:58:25 GMT

Hi Filip,

Have you tried rotating the PTX about the PTOrigin by 90 degrees to determine the PTY ?

or)

the other option is to first create a vector from PTX to PTOrigin and then use the "Vector3d.GetPerpendicularVector" method using that vector.

Re: UCS 3points

_gile — Mon, 05 Nov 2012 07:28:22 GMT

Hi,

you can use the cross product of X axis and Y axis to define the Z axis, then recalculate Y axis with the cross product of z axis and X axis.

Here's a quick and dirty (no error handling if points are overlapped or if xaxis is parallel to Y axis)

        private CoordinateSystem3d UcsBy3points(Point3d org, Point3d ptX, Point3d ptY)
        {
            Vector3d xAxis = org.GetVectorTo(ptX).GetNormal();
            Vector3d zAxis = xAxis.CrossProduct(org.GetVectorTo(ptY)).GetNormal();
            Vector3d yAxis = zAxis.CrossProduct(xAxis).GetNormal();
            return new CoordinateSystem3d(org, xAxis, yAxis);
        }

Re: UCS 3points

Anonymous — Mon, 05 Nov 2012 08:33:47 GMT

Hi,

I think the solution with "Vector3d.GetPerpendicularVector" seems easy, but I've tried it without the desired result. The UCS is not always correct because some times the Y-direction must point to the negative Z-direction (from World UCS)

your second solutions seems more like it. I will try it in a few days and report the result.

thanks in advance

best

Filip

Re: UCS 3points

_gile — Mon, 05 Nov 2012 08:45:07 GMT

The way I purposed will also work whatever the new XY plane (i.e. 3D UCS rotated on X and/or Y axis).

Re: UCS 3points

Anonymous — Thu, 10 Jan 2013 11:54:01 GMT

Hi Gilles

I was indeed incorrect. I tried your code again and it works fine now.

Thx

Filip