4.4. Tutorial: Optimising the surface geometry

Starting Point

Although not essential, it is usually better to have an initial surface generated from which the optimisation can start. You will also need to have a some or all of your images masked accurately since the model will be optimised to fit these masks.

For highly patterned objects, you may wish to generate a point cloud see Generating a 3D Point Cloud to capture concave regions not visible from the masks alone.

You can also create additional silhouette images and edit these if you want to capture particular features as described in the Adding synthetic silhouettes tutorial.

Note: Optimisation will discard any surface texture generated, but it will keep in place any clipping you have performed, so it is better to clip away the stand beforehand.

Step 1

Open the Surface Wizard by clicking the Generate surface... button and choose "Optimise Surface" then click the Next > button to go to the Surface Optimisation Window.

Step 2

If you have generated a point cloud you can choose to include the points in the optimisation by checking the "Use Point Cloud" checkbox or ignore the points by unchecking the box.

Uncheck the "Use Masks" if you have point data as well as masked images and do not want to use the masks.

If you have a smooth organically shaped object, choose "smooth approximation" to generate a smoothed mesh with few corners. Otherwise, either leave the default "reasonable accuracy" set or choose "exact fit" if you are confident that your masks are very accurate and you want the surface to exactly fit all the details on them.

If you have edited the masks to remove unwanted regions in just a few of the images (e.g. the stand or a subpart of the object) you will need to make sure the "Clip masks to current geometry" option is selected. This will prevent the non-edited masks affecting the geometry (and growing back the removed region).

TIP:	If you have a lot of images in your project or the silhouettes are particularly complex, optimisation can be slow, so it is a good idea to limit the number of images used at each optimisation step by setting the "Number of masks used" parameter.

The "Optimise camera orientations" option will allow the camera parameters to be refined during the optimisation. This can be useful if you have no calibration mat and have used manual markers to estimate the camera parameters. If your manually placed markers are slightly inaccurate then the resulting camera parameters may be improved using the optimimsation step.

The "Locally Adaptive Smoothing" option should normally be selected. This option results in the mesh density (size of triangles) being adapted to the data available.

Click the Next > button to start the optimisation process.

Step 3

After some initialisation, 3DSOM Pro will start to modify the surface, gradually smoothing it while ensuring the features on the silhouettes are captured.

During this process, you can see the current geometry and look around the model by rotating it in the View Model Window as usual. At this stage, the mesh will be displayed with the maximum number of triangles, and will only be reduced to your chosen decimation level when optimisation finishes.

Use the Pause button to halt the optimisation while you look at the results and then hit the Continue button to resume optimisation.

Use the Hide button to hide the wizard dialog allowing you to see more of the model. The progress will be displayed in the status bar.

TIP:	If you have generated a point cloud select the Show surface only button to hide the points and view the surface clearly. For optimising with a point cloud we recommend a machine with a multi-core high performance processor is used as the process will be computer intensive.

If you want to change the parameters, click the < Back button at any point to return to the previous step and edit them (for instance if the optimisation is proceeding very slowly you could reduce the number of images being used).

Step 4

You can either leave the optimisation to finish completely, or interrupt it when you are happy with the current surface. Click the Close button to leave the Surface Wizard keeping the current mesh, or click the Next > button to go on to fit a subdivision surface to the mesh (as described in the Improving the geometry with subdivision surfaces tutorial).

During Optimisation at high quality settings, several (smoother) partial results will be made available on the "undo" stack so you can unwind the process in several steps using the Undo model or mask change button and Redo model or mask change button to go forward.

You can also edit the surface geometry using the tools described in the The View Model Window.