[vtkusers] Coordinate conversions (World-Display)

[Daniel Haehn]

Pat,

looks good - I will use the static methods.

Thank you,
Daniel

On Sep 8, 2010, at 6:44 PM, pat marion wrote:

> Sadly, yes, this is the way to do it.  If you want, there is a class that offers static convenience methods:
> 
> static void vtkInteractorObserver::ComputeDisplayToWorld (vtkRenderer *ren, double x, double y, double z, double worldPt[4])
> static void vtkInteractorObserver::ComputeWorldToDisplay (vtkRenderer *ren, double x, double y, double z, double displayPt[3])
> 
> But if you look at the implementation...
> 
> void vtkInteractorObserver::ComputeWorldToDisplay(vtkRenderer *ren,
>                                                   double x, 
>                                                   double y,
>                                                   double z, 
>                                                   double displayPt[3])
> {
>   ren->SetWorldPoint(x, y, z, 1.0);
>   ren->WorldToDisplay();
>   ren->GetDisplayPoint(displayPt);
> }
> 
> One comment about your code... I'd be careful returning a double* like that.  You don't own that memory, it could change at any time.
> 
> Pat
> 
> On Wed, Sep 8, 2010 at 1:42 PM, Daniel Haehn <haehn at bwh.harvard.edu> wrote:
> Hi VTK experts,
> 
> I use the following functions to convert between World and Display coordinates and vice versa. I found the method on the mailing list or in some other code.
> 
> Isn't there an easier way to do that? Is it correct at all and is it robust?
> 
> this->GetRenderer is a vtkRenderer.
> 
> //---------------------------------------------------------------------------
> /// Convert display to world coordinates
> double* vtkMRMLAnnotationThreeDViewDisplayableManager::GetDisplayToWorldCoordinates(double x, double y)
> {
>  double coordinates[3];
>  coordinates[0]=(double)x;
>  coordinates[1]=(double)y;
>  coordinates[2]=0;
> 
>  this->GetRenderer()->SetDisplayPoint(coordinates);
>  this->GetRenderer()->DisplayToView();
>  this->GetRenderer()->GetViewPoint(coordinates);
>  this->GetRenderer()->ViewToWorld();
>  return this->GetRenderer()->GetWorldPoint();
> 
> }
> 
> //---------------------------------------------------------------------------
> /// Convert world to display coordinates
> double* vtkMRMLAnnotationThreeDViewDisplayableManager::GetWorldToDisplayCoordinates(double * worldPoints)
> {
> 
>  vtkDebugMacro("GetWorldToDisplayCoordinates: RAS " << worldPoints[0] << ", " << worldPoints[1] << ", " << worldPoints[2])
> 
>  double * displayCoordinates;
> 
>  this->GetRenderer()->SetWorldPoint(worldPoints);
>  this->GetRenderer()->WorldToView();
>  displayCoordinates = this->GetRenderer()->GetViewPoint();
>  this->GetRenderer()->ViewToDisplay();
> 
>  double * output = this->GetRenderer()->GetDisplayPoint();
> 
>  vtkDebugMacro("GetWorldToDisplayCoordinates: Display " << output[0] << ", " << output[1])
> 
>  return output;
> 
> }
> 
> Thank you,
> Daniel
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