Chapter 5: Meshing the points
This Dense Point Cloud which may incorporate tens of millions of points can as a next step be used as the basis for creating a mesh based upon the point cloud to which the original images can be finally be applied as a texture (Powlesland 2016: 21). This way, we transform our point cloud into a solid 3D object that will become a photorealistic texture in the next chapter. This object can then later be used to be processed in any 3D software. You can use the scanned object as objects in a 3D scene or upload the data onto a 3D viewer available on the internet to provide for others to see your work. The first step however is to connect all the points to create a solid 3D object, in other words to build our mesh.
Building a Mesh
After building the Dense Point Cloud, your model should look like the image above. If not, make sure, that the Dense Cloud-button is selected. Open the Workflow menu and hit Build Mesh.... For this example, we will use the Arbitrary surface type, Dense Cloud source data and Medium face count. Hit the OK-button.
Additional information: The Surface type option helps the software to build the mesh. Arbitrary is chosen for closed objects like statues, pottery or buildings. Height field is chosen for planar surfaces like terrains, the façade of a building or bas-reliefs. Here, the software does not try to close the object and therefore does not use so much computer power.
Source data specifies the data the building of the mesh is relying on. You can build the mesh also on the Sparse Point Cloud, as this will go much faster. For better results, we should rely on the Dense Point Cloud however.
Face count specifies the maximum number of polygons in the final 3D model. The settings High, Medium and Low correspond each to a fraction of the number of points on the previously generated Dense Point Cloud. The higher the value, the finer the 3D model and the longer the calculation.
In the Advanced settings, the Interpolation setting helps with the filling of gaps in the model. If the interpolation is disabled, gaps in the model remain gaps in the final 3D data. With this option enabled, the software will fill most of the gaps relying on the Dense Point Cloud. Some gaps can remain. The Extrapolated option will generate a gap-less model, but the accuracy is therefore not very high.
Seeing the model
Again, to be able to see the mesh, you need to click on the Model Shaded-button right next to the Dense Cloud-button. As you can see the model is now solid and it looks actually coloured. The colours however are still from the point cloud, so we need to do one last step.
Bibliography
- Powlesland, Dominic 2016: β3Di - Enhancing the Record, Extending the Returns, 3D Imaging from Free Range Photography and Its Application during Excavation.β In: The Three Dimensions of Archaeology. Proceedings of the XVII UISPP World Congress (1β7 September 2014, Burgos, Spain), edited by Hans Kamermans, Wieke de Neef, Chiara Piccoli, Axel G. Posluschny, and Roberto Scopigno, 13β32. Volume 7/Sessions A4b and A12. Oxford: Archaeopress.