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Velocity: 3-D Visualization

1. The Bottle
2. The Pelvis

The Bottle

Two windows will open, a control panel and a 3D graphics display window. You will use Display to view your water bottle reconstruction using several light sources, to smooth the surface, make simple distance measurements, reduce the numbers of triangles in the surface and finally to save the model in STL format.

Rendering Tools

In the control panel, click on the File Open icon and then, from the File Chooser, select your 3D bottle reconstruction.

Lets put more light on the subject! Click on the Lights button and select three lights: WhiteZPlus, background2 and vangogh. (Lights are defined in the text file, .lgts , located in the velocity/ data directory). Click on OK when all lights have been selected.

Place the mouse cursor in the 3D graphics window and then, while pressing and holding the left mouse button, rotate the model to the view shown in the figure above.

Click on the BG Color button and select a background color for the display. (Colors are stored in the text file, . background , located in the velocity/ data directory).

Display includes several additional functions for transforming and saving model coordinates (TxForm button), for capturing images to disk in TIF format (Capture button), and for viewing your model in stereo mode when your computers video adapter is equipped to use special glasses such as CrystalEyes by Stereographics Corp. Information on any of these functions can be accessed from the Help > Velocity2 Pro Manual menu, or by clicking the context help cursor (?) on any button or control of interest.

Smoothing and Triangle Reduction Tools

You will now use several tools to refine and analyze your model. You may notice that the surface of the model appears rough. This is due to several factors: choice of Pixel Sampling in Surfer, noise in the image data, and the discrete nature of digitized image data. Display can smooth the surface to reduce these effects in two ways: local vertex coordinate averaging and triangle reduction to remove small triangles.

To apply local vertex coordinate averaging, click on the Smooth button in the control panel. Triangle reduction operates to collect small triangles into larger ones in regions of the surface that are relatively flat.

Click on the Reduce button in the control panel toolbar. The Triangle Reduction toolbox will be displayed, as shown at the right.

Flatness within a local region of the surface is specified in terms of the maximum deviation among local triangle surface normal vectors (in angular degrees) below which the local surface can be taken to be flat.

Use the Flatness slider to set a value of about 20 degrees. Click on the Perform button.

Triangle reduction will be applied iteratively until the number of triangles removed from the surface on any given iteration falls below the Terminate Count. Progress is shown by a plot of the current number of triangles in the model against the iteration number.

The Pelvis

Click on the Smooth button to remove some of the sampling artifact and noise.

Click on the Delete button in the control panel toolbar and then on the Yes button in the Before measurements can be made ... dialog.

When analysis is complete, position the model as shown in the figure to the left.

The Delete (and Measurement) tools let you view a 3D model in one of two different ways: as surfaces and as 3D objects. Surfaces can be either exterior or interior and are assigned to viewing levels beginning with the primary exterior surfaces, which are at level 1. Level 2 surfaces are interior surfaces of level 1, and so forth. 3D objects are defined by an exterior surface and all interior surfaces contained therein (see the Technical Reference Manual for more information). Suffice it to say, the pelvic bones are level 1 3D objects and are made up of level 1 exterior and level 2 interior surfaces.

Click on the 3D Obj button in the Viewing Mode controls.

Click on View Level and select Level 1 from the drop- down menu. As shown in the # at Level: text box, there are five 3D objects in this model at level 1. One is the coccyx, each femur and iliac (because they are touching) represent two more, and the fourth and fifth are small artifacts.

Delete the coccyx using Pick Delete mode. Click on the Pick Delete button.

Now place the mouse cursor over the coccyx and click on the middle mouse button. The coccyx will be redrawn in red, indicating that you have selected it for deletion.

Click on the Perform button to delete the coccyx.

There are two small 3D objects, one of which is barely visible, that you should delete. Click on the Delete < button to select deletion based on size, in this case objects less than a certain volume.

Sizes of 3D objects in the model are shown by the histogram plot. The two sliders below the histogram, labeled Min Limit and Max Limit, select objects to be deleted based on their size - the upper slider controls the minimum size and the lower slider the maximum size. With the Delete < function selected, all 3D objects less than the volume set in Min Limit will be deleted.

Vary the Min Limit slider and set the yellow line just to the right of the first peak in the histogram.

Now, click on the Perform button.

If at any time you delete the wrong object, click on Undo Del to bring it back.

At this point the # at Level text box should be two, meaning that there are now just the left and right femur and iliac bones (each femur and its associated iliac being one 3D object because we left them touching when reconstructed).

Finally, you will examine the interior surfaces of the bones and delete them as well.

Click on the Surface button in Viewing Mode.

Click on the View Level button and select Level 2 from the drop- down menu. Notice that there are approximately 80 surfaces at this level, i. e. porosities in the bone.

Set the Transparency slider to about 0. 8.

Select < Delete > . In this mode, all surfaces at surface level 2 whose volumes fall between Min Limit and Max Limit will be deleted when you click on Perform.

Set the Min Limit to the far left position and the Max Limit to the far right, that is, select all surfaces at this level for deletion.

The model should appear as shown in the bottom figure to the left. Exterior surfaces are rendered in transparency so you can see through them to the interior surfaces that are now highlighted in red.

Click on Perform to delete all interior surfaces at level 2.