[vtkusers] Calculating the distance between two polyDatas

[Robbie Banks]

Hi there,

If you  have the polydata and create a vtkDataSet from this, then you can
use the routine below to determine the distance

double cords1[3];
double cords2[3];
double distance = 0.0;

pData->GetPoint(i-1,cords1);
pData->GetPoint(i, cords2);
distance += sqrt(vtkMath::Distance2BetweenPoints(cords1, cords2));

where pData is the vtkDataset created from grabbing the two points of
interest from your vtkPolydata

Cheers
Robbie

-----Original Message-----
From: vtkusers-bounces at vtk.org [mailto:vtkusers-bounces at vtk.org] On Behalf
Of agerlach
Sent: Thursday, February 03, 2011 9:43 AM
To: vtkusers at vtk.org
Subject: [vtkusers] Calculating the distance between two polyDatas


All,

I have two polyDatas that represent the same "object" (imagine one as a 3D
mesh derived from a 3D CAD model (call this polyData A) and the other as a
3D mesh obtained by 3D scanning a real-world object manufactured from the
CAD model (call this polyData B). Currently I can load both models and align
them, but now I what to visualize the difference between them by rendering
polyData A and then color the surface based on the "difference" between the
polyDatas.

I have seen several example that implement this by taking each point in A
and then searching for the closest point in B and calculating this
difference. However, I would like to specify the point used for calculating
the difference as the point in B closest to the surface normal extended from
the point in A.

Example: take point 1 in A and its surface normal. Then find the cell in B
that intersects with point 1's surface normal. Then approximate the location
on the cell that the normal intersects. This point - point 1 then becomes
the difference used in the visualization. I guess my question is what is the
best way to do this?

It looks like vtkCellLocator::intersectWithLine(...) will work, but I am a
little confused on how that method works. According to the documentation
this can return the cellId as well as a point. Is this point the centroid of
the cell, the 1 of 3 points that define the cell that is closest to the
intersection, or the point of intersection?

Thanks
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