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

[Dan Lipsa]

Not sure what is going on. Do the objects you are rendering have the same
world coordinates? Are both renderers added to the rendering window?
Here is an example with multiple renderer (they are over different
viewports but they could have the same viewport as well)
http://www.vtk.org/Wiki/VTK/Examples/Cxx/Visualization/MultipleViewports

On Tue, May 23, 2017 at 11:39 AM, Bill Q <bill.q.hdp at gmail.com> wrote:

> I just gave it a try. But when I added another renderer into the window
> that I used for text actors, it overlaps and covered the first renderer. So
> the first renderer won't show up. Is there a solution?
>
> Many thanks.
>
>
> Bill
>
> On Tue, May 23, 2017 at 10:16 PM, Dan Lipsa <dan.lipsa at kitware.com> wrote:
>
>> 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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>>
>
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