# Visualize the Leaning Tower of Pisa (or San Francisco's Millennium Tower)

I’m looking for inspiration on how to present my data. I can do the math part. What I’m looking for is how to present it.

Imagine a multistory building of equally-spaced floors, either cylindrical (like a grain silo) or square (like a skyscraper) in cross-section. Each floor has a sensor on the corners (for square) or compass points (for cylinder) that measures the distance to the ground and the “cross-wise” distance (eg. horizontal rotation) from where that corner should be. I want to visualize how much each floor is tipping or twisting and on what axis based on the coordinates of its four sensors.

For a 10+1 floor building, I’d have 40 sensors with 2 readings each, vertical and sideways.

I can think of a few ways you might visualize the deformation:

1 - Represent the building in wireframe. At each vertex where you have a sensor, display the sensor’s Cartesian orientation with a small set of x-y-z axes. An undeformed sensor will align with the rectilinear axes of the wireframe, a deformed sensor will have an x-y-z twist.

2 - Create two wireframe representations of the building, one undeformed, the other with vertexes in their deformed positions and overlay them.

3 - As in (1), but omit the building wireframe (just show the sets of axes).

4 - Animate (2) by alternately displaying the deformed / undeformed wireframes.

It would be nice to incorporate color, but I can’t think of a way to use a single color to represent a multidimensional change. There are probably abstract ways to represent your data, but it is probably more important to set the context by overlaying the data on a model of the building.

Thanks, those sound great. Can you point me in the direction of suitable VTK classes to represent that?

I’ve used VTK a few years ago to display a heat map to represent deformities in a surface that’s ideally flat, so I’m familiar with VTK’s architecture and how to build it and incorporate it into my wxWidgets-based GUI. But VTK is so feature-rich that it’s hard to find the right trees for an application in the forest.

For color, I could probably display each sensor in a spectrum based on the degree of total rotation, to indicate a degree of “badness”.

Since the distortion is likely to be small, I might add a scaling slider to exaggerate the error for greater visibility.

I am a real newbie with VTK, and as you say, it is overwhelmingly feature-rich.

There is the wireframe example for starters. That can represent the undeformed wireframe, and by a different choice of data element (other than image data) like possibly polydata, the deformed wireframe as well.

For axes, there is vtkAxesActor using which you would create one actor per vertex, translating, rotating, and scaling according to location and deformation.

Perfect! That gives me plenty of hints to put this together. From other reading, it sounds like I can attach those to an “assembly” actor for easy interaction.