matrix datatype in Rhinocommon

Hi,

I want to perform matrix operations (multiply, invert, etc.) and I know this can be done using two dimensional arrays and some custom functions. I tried this example code and it worked.

But it seems there is a special matrix class available in the Rhinocommon. Could anyone explain how to use it? I'm a beginner in programming and there're no examples in the SDK to start with...

Thanks,

Jacek

Replies to This Discussion

Permalink Reply by Mateusz Zwierzycki on February 19, 2012 at 5:55am

i suppose that this is transformation matrix...

Permalink Reply by Jacek Jaskólski on February 19, 2012 at 6:00am

In the particular case I'm thinking to implement it - yes, but I'm also interrested in the general (any) matrix operations.

Permalink Reply by Giulio Piacentino on February 19, 2012 at 7:46am

Hi Jacek,

Rhino.Geometry.Matrix
Represents an arbitrarily sized matrix of double-precision floating point numbers. If you are working with a 4x4 matrix, then you may want to use the Transform class instead
Rhino.Geometry.Transform
Represents the values in a 4x4 transform matrix.
This is parallel to C++ ON_Xform.

So Matrix is general and Transform is meant to be a transformation matrix only.

For an example, see: http://wiki.mcneel.com/developer/rhinocommonsamples/transformbrep

Is this helpful to get started?

Thanks,

- Giulio
_______________
giulio@mcneel.com

Permalink Reply by Jacek Jaskólski on February 19, 2012 at 8:13am

Hi Giulio,

This is very helpful, thanks.

Though it still is unclear to me how to:

1. declare a Matrix type with sepcifying it's dimensions

2. set data to a Matrix type (with Transform I can access each element directly, ie. M12, or use the predefined transformations such as translation, rotation, etc)

2. convert Rhino.Geometry.Transform to Rhino.Geometry.Matrix and back (for example to do an inversion)

Permalink Reply by Giulio Piacentino on February 19, 2012 at 8:43am

It seems like Andrew below here answered all these questions. He wrote the answer in C#.

Instantiating and index retrieval is pretty much the language default (new keyword and indexers [i, j]). In Vb.Net it would be New and (i, j).

- Giulio
_______________
giulio@mcneel.com

Permalink Reply by Andrew Heumann on February 19, 2012 at 8:25am

Because the scripting components don't accept matrix types by default, if you want to operate on a matrix generated in GH, you'll have to bring it in as System.Object and cast it. At its simplest this looks a bit like this:

private void RunScript(System.Object x, ref object A) { Transform tx = (Transform) x; }

To be a little more sophisticated you might want to build in some form of error checking to verify that the cast worked. You can convert this into a more generic matrix with the Matrix constructor that accepts a transform:

Matrix mx = new Matrix(tx);

Once you've got your matrix in whatever form you need it, you can call any of the functions in the SDK pages that Giulio linked to. If your goal is to invert one of the GH transformation matrices, something like the following will do the trick:

Transform tx = (Transform) x; Transform Inverse = new Transform(); tx.TryGetInverse(out Inverse); A = Inverse;

I hope that's helpful!

Permalink Reply by Andrew Heumann on February 19, 2012 at 8:30am

And just saw your other questions:

1. Matrix mx = new Matrix(5, 6); will declare a new 5x6 Matrix

2. using the "item" property you can set and get specific matrix values - mx[3,2] = 2.0; will set the value of the cell at 3,2.

3. You don't need to convert back and forth to do an inversion, as my example above shows. Not sure what the easiest way would be to convert a matrix back to a transform.

Permalink Reply by Andrew Heumann on February 19, 2012 at 8:38am

Here's a function that does it, though there might be an easier way.

Transform TFromMatrix(Matrix m){ Transform T = new Transform(); if(m.ColumnCount == 4 && m.RowCount == 4){ for(int i = 0;i < 4;i++){ for(int j = 0;j < 4;j++){ T[i, j] = m[i, j]; } } } return T; }