[vtk-developers] [VTK 0012993]: vtkImageData::FindCell returns valid cellId for outside points

[Mantis Bug Tracker]

The following issue has been SUBMITTED. 
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http://vtk.org/Bug/view.php?id=12993 
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Reported By:                Bernd Hentschel
Assigned To:                
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Project:                    VTK
Issue ID:                   12993
Category:                   (No Category)
Reproducibility:            have not tried
Severity:                   minor
Priority:                   high
Status:                     backlog
Project:                    TBD 
Type:                       incorrect functionality 
Resolution:                 open
Fixed in Version:           
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Date Submitted:             2012-03-13 12:20 EDT
Last Modified:              2012-03-13 12:20 EDT
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Summary:                    vtkImageData::FindCell returns valid cellId for
outside points
Description: 
vtkImageData::FindCell will return a valid cellId (>=0) for points that lie
outside the data set bounds. This should never happen for cartesian grids. More
specifically, I noticed that only points that lie outside the domain but within
one spacing in either dimension are handled in this fashion. Please find
attached a short test program illustrating the issue.

Looking at the code of FindCell(...) and
vtkImageData::ComputeStructuredCoordinates(...) it looks like this is a
combination of a truncation error when moving from physical to grid coordinates
combined with an issue in the subsequent computation of the corresponding
cellId. 

As a short term fix, I might suggest testing the input coords against the bounds
in the first place (early exit). However, I wondered why the mapping to a grid
point is made in the first place, because it's pretty straightforward to compute
the correct cellId from the input coords right away without referring to grid
points altogether.
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Issue History 
Date Modified    Username       Field                    Change               
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2012-03-13 12:20 Bernd HentschelNew Issue                                    
2012-03-13 12:20 Bernd HentschelFile Added: BugReportVtkImageData.cpp           
        
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