How to build vtkPolyData based on the information within a txt file

Question

I have a txt file which contains a set of 3 Dimensional data points and I would like to create a vtkPolyData based on those points.

In the file, I have the number of points on the first line, in my case they are 6 x 6. And after that the actual coordinates of each point. The content of the file is like this.

6 6 
1 1 3
2 1 3.4
3 1 3.6
4 1 3.6
5 1 3.4
6 1 3
1 2 3
2 2 3.8
3 2 4.2
4 2 4.2
5 2 3.8
6 2 3
1 3 3
2 3 3
3 3 3
4 3 3
5 3 3
6 3 3
1 4 3
2 4 3
3 4 3
4 4 3
5 4 3
6 4 3
1 5 3
2 5 3.8
3 5 4.2
4 5 4.2
5 5 3.8
6 5 3
1 6 3
2 6 3.4
3 6 3.6
4 6 3.6
5 6 3.4
6 6 3

How can I build a vtkPolyData structure with a txt file with this data?

Answer 1

It looks to me like you have a regularly gridded series of points, right? If so, vtkImageData might be a better choice. You can always use a geometry filter afterwards to convert to polydata if you really need it that way.

1. Create a vtkImageData instance.
2. Set its dimensions to (6, 6, 1) (the third dimension is ignored).
3. Set its data type to an appropriate type (float or double, I guess).
4. Call AllocateScalars();

5. If in C++,

   1. call GetScalarPointer() and cast it to the data type set in 3.
   2. This pointer will point to an array of size 36. You can just fill each point as you would normally.

6. If in another language (TCL/Python/Java), call SetScalarComponentFromFloat on the image data, with the arguments (x, y, 0, 0, value). The first 0 is the 3rd dimension and the second is for the first component.

This will give you a grid, and it'll be far more memory efficient than a polydata.

If you want to visualize only the points, use a vtkDataSetMapper, and setup the actor's property with SetRepresentationToPoints(), setting an appropriate point size. That will do a simple job of visualization.

Answer 2

Are these examples useful? In particular, this does generation of points and polygons, so it should be possible to adapt. The core seems to be (with lots left out):

# ...
vtkPolyData shell
vtkFloatPoints points
vtkCellArray strips

# Generate points...
loop {
   ...
   points InsertPoint $k $x0 $x1 $x2
}
shell SetPoints points
points Delete

# Generate triangles/polygons...
loop {
   strips InsertNextCell $NP2
   # ...
   strips InsertCellPoint [expr $kb +$ke ]
   # ...
   strips InsertCellPoint [expr $kb +$ke ]
}
shell SetStrips strips
strips Delete

# ...