[vtkusers] Tolerance of InsertNextPoint in python

[Brett Tully]

Hi David,
I am using the VTK version from the Ubuntu repositories and just checked to
see that it is indeed 5.6.
Thanks,
Brett

On Mon, Apr 30, 2012 at 6:14 PM, David Gobbi <david.gobbi at gmail.com> wrote:

> I can see that maybe in VTK 5.6 or earlier you might see results like
> that, but not in VTK 5.8 or 5.10.  I just tested VTK 5.10 to be sure.
> What version of VTK are you using?
>
>  - David
>
>
>
> On Mon, Apr 30, 2012 at 10:33 AM, Brett Tully <brett.tully at oxyntix.com>
> wrote:
> > I am not sure if this is a bug, by design, or just an intricacy of Python
> > wrappers, but I have found a difference between VTK points depending on
> if
> > they are created by passing in x, y, z coordinates, or by passing a 3
> > element array [x, y, z]. The first method gives a true double precision
> > point as requested by SetDataTypeToDouble, where as the second method
> still
> > results in a single precision point. I have fixed our code to ensure
> double
> > precision, but I thought I would post it here for future reference.
> >
> > Brett
> >
> > import vtk
> > vtk_points = vtk.vtkPoints()
> > vtk_points.SetDataTypeToDouble()
> > e = [0.0, 0.0065, 0.0]
> >
> > # pass in the point using its individual components
> > e1_id = vtk_points.InsertNextPoint(e[0], e[1], e[2])
> > p_e1 = vtk_points.GetPoint(e1_id)
> >
> > # pass in the point as an array
> > e2_id = vtk_points.InsertNextPoint(e)
> > p_e2 = vtk_points.GetPoint(e2_id)
> >
> > # check the difference between the two methods
> > print p_e1, p_e2
> > print (p_e1[0] - p_e2[0]), (p_e1[1] - p_e2[1]), (p_e1[2] - p_e2[2])
> >
> > # gives
> > # (0.0, 0.0065, 0.0) (0.0, 0.006500000134110451, 0.0)
> > # 0.0 -1.34110451043e-10 0.0
> >
> > On Tue, Apr 3, 2012 at 1:43 PM, David Gobbi <david.gobbi at gmail.com>
> wrote:
> >>
> >> Hi Brett,
> >>
> >> The default type of vtkPoints is "float".  If you need more precision,
> >> then you can change the precision to "double":
> >>
> >> vtk_points = vtk.vtkPoints()
> >> vtk_points.SetDataTypeToDouble()
> >>
> >> This is true in both C++ and Python.
> >>
> >>  - David
> >>
> >>
> >> On Tue, Apr 3, 2012 at 6:22 AM, Brett Tully <brett.tully at oxyntix.com>
> >> wrote:
> >> > Dear all,
> >> >
> >> > I am finding that vtkPoints.InsertNextPoint when called from python
> does
> >> > not
> >> > return a point where I want it -- it seems to be out by ~1e-10 -- is
> >> > there a
> >> > way to set the tolerance of this function or improve its location to
> be
> >> > more
> >> > precise than 1e-10? Or is this due to python floats?
> >> >
> >> > Thanks,
> >> > Brett.
> >> >
> >> > I.e. the following python:
> >> >
> >> > import vtk
> >> > vtk_points = vtk.vtkPoints()
> >> > e = [0.0, 0.0065, 0.0]
> >> > e_id = vtk_points.InsertNextPoint(*e)
> >> > p_e = vtk_points.GetPoint(e_id)
> >> > print p_e, e
> >> > print (e[0] - p_e[0]), (e[1] - p_e[1]), (e[2] - p_e[2])
> >> >
> >> > # gives
> >> > # (0.0, 0.006500000134110451, 0.0) [0.0, 0.0065, 0.0]
> >> > # 0.0 -1.34110451043e-10 0.0
> >
> >
>
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