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Velocity: Surface Reconstruction

1. The Bottle
2. The Pelvis

The Bottle

Using the water bottle data set, you will now use Image to perform a simple gray-level threshold reconstruction. Notice, when Image is first run, it already places you in the Logic operations. Image
allows you to perform many different kinds of operations on the image set. These include: gray-level enhancement, filtering, ROI, logical, and masking operations. These can be used in combination or separately to achieve segmentation of objects in the image data.

Clicking on Flood Fill causes the threshold meter to be displayed. Moving the slider highlights all pixels whose gray values are greater than or equal to the slider setting. You can also type a threshold value in the text box at the base of the meter.

Adjust the threshold meter so that the red areas in the image closely approximate the circumference of the water bottle. (Try using the Zoom In and Zoom out functions to get a better view of the data).

Dynamically view your images by scrolling through them using the filmstrip scroll bar. Drag the top edge of the filmstrip window to expose more of the mosaic. As you scroll through the set, evaluate whether the correct threshold has been set. You should not pick-up any gray values outside of the
white area defined by the water bottle. Note the gray value shown in the text box at the bottom of the meter. You will need this number when reconstructing the water bottle. We suggest you use a threshold setting of 25.

Surfer is the module in Velocity 2 Pro that creates the 3D model from volumetric image data. Once Surfer is run, another threshold meter will be visible in the control panel. To continue with the workshop and produce your 3D model:

Click on the toolbar button labeled Surfer.

 In the Dimensions box, click on the Pixel Sampling button. From the menu choose a value of 3. This tells Surfer to sample the image data on a 3x3 grid of pixels when generating surface data. For this exercise, it is not necessary to use 1, the finest sampling setting.

Set the Surfer threshold meter to the value determined in Steps 5 & 6 above (25 was suggested).

Click on the Model File button. Make sure you first select the desired directory for storing results. In the Selection text box in File Chooser, type in a name for your model file.

Leave the File Chooser by clicking on OK.

Select the Material button. You must specify a surface material (color choice). Try bronze for your reconstruction and then click on OK.

Click on the Perform button.

In the status window section of the control panel you will see messages detailing the progress of the reconstruction, numbers of triangles produced, and the processing time. The 3D model file is automatically saved at the end of the reconstruction.

The Pelvis

Set the threshold to the value noted in Step 28 above (we recommend 165).

Use a Pixel Sampling value of 2.

In Mask Logical Operations, click on the tilde symbol key (~) and then on 3. This tells Surfer to use Mask Three during reconstruction, specifically the logical complement of Mask Three. The effect is to mask each image with logical 1s everywhere except where the table pad occurs.

Click on Per form. Surfer will store a model containing approximately 120,000 triangles.

You have now successfully created a 3D model of the pelvic bones.