[vtkusers] Issues with coordinate conversion, possible VTK bugs?

[Dan Lipsa]

I think moving those text actors on a different renderer will solve your
problem.

Dan


On Tue, May 23, 2017 at 9:40 AM, Bill Q <bill.q.hdp at gmail.com> wrote:

> Hi Dan,
> Thanks a lot for the reply. Yes, that's exactly the case. If I remove the
> text actors, the world picker would return the correct coordinates. So,
> what method should I use in order to get the correct coordinates no matter
> how many actors I put in with the dicom image reader actor?
>
> Many thanks.
>
>
> Bill
>
> On Mon, May 22, 2017 at 10:04 PM, Dan Lipsa <dan.lipsa at kitware.com> wrote:
>
>> Bill,
>> For display_to_world, the picker picks up only what is visible (closes to
>> the camera). You might have several objects (several values in world
>> coordinates) that end up over the same display coordinate. This might
>> explain why adding those text actors changes what you pick.
>>
>> Dan
>>
>>
>>
>> On Sun, May 21, 2017 at 5:25 AM, Bill Q <bill.q.hdp at gmail.com> wrote:
>>
>>> Can anybody help? Many thanks.
>>>
>>> Many thanks.
>>>
>>>
>>> Bill
>>>
>>> On Fri, May 19, 2017 at 11:20 PM, Bill Q <bill.q.hdp at gmail.com> wrote:
>>>
>>>> Hello Everyone,
>>>> I encountered a weird problem in coordinate conversion.
>>>>
>>>> In order to check the accuracy, I converted from display to world, and
>>>> from world back to display. Using the following ways:
>>>>
>>>>
>>>> *self.world_picker = vtk.vtkWorldPointPicker()*
>>>>
>>>> *def *display_to_world(self, pt):
>>>>     self.world_picker.Pick(pt[0], pt[1], 0, self.ren)
>>>>     picker_pt = self.world_picker.GetPickPosition()
>>>>     picker_pt = (picker_pt[0], picker_pt[1], 0)
>>>>     *return *picker_pt
>>>>
>>>> *def *world_to_display(self, pt):
>>>>     *if *len(pt) == 3:
>>>>         pt = pt + (1.0,)
>>>>     *elif *len(pt) == 2:
>>>>         pt = pt + (0.0, 1.0)
>>>>     self.ren.SetWorldPoint(pt)
>>>>     self.ren.WorldToDisplay()
>>>>     pt = self.ren.GetDisplayPoint()
>>>>     pt = (pt[0], pt[1])
>>>>     *return *pt
>>>>
>>>> pt = [5, 5]
>>>>
>>>> world_pt = self. world_to_display(pt)
>>>>
>>>> display_pt = self. world_to_display(world_pt)
>>>> In some cases, it's quite accurate, which means pt equals display_pt.
>>>> But, in some cases, the result is simply wrong. For example, for (5, 5),
>>>> after conversions back to display, the coordinate becomes (20.89, 20.89).
>>>>
>>>> Any ideas?
>>>>
>>>>
>>>> Many thanks.
>>>>
>>>>
>>>> Bill
>>>>
>>>
>>>
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