Tutotrial_02: Add and access properties of a point cloud

In Easy3D, all actual 3D data are stored as per-element (e.g., vertex, edge, and face) properties. A model can have multiple properties and the properties can be accessed by their names. So it is important to give each property a unique name. Easy3D will pop up a warning if you attempt to create a property with an already used name.

	// Assume you have a point cloud (loaded from a file or created by your algorithm).
	PointCloud* cloud = ...

	// Let's add a random color to each point. 
        // We give this property a name "v:color". Here "v:" is optional and it just indicates
        // that this property 
	// is defined on the vertices. You will later see properties defined one edges (use 
        // "e:") and faces (use "f:") for surface meshes.
	PointCloud::Vertex_property<vec3> colors = cloud->add_vertex_property<vec3>("v:color");
	for (auto v : cloud->vertices())	// iterate over all vertices
		colors[v] = random_color();	// assign a random color to point 'v'

	// You can use the get_vertex_property() function to access the named properties.
	// Below I show you how to access the xyz coordinates and color of each point.
	// Here we simply print the coordinates and colors.

	// The point coordinates are stored as a per-point property 'v:point'.
	PointCloud::Vertex_property<vec3> points = cloud->get_vertex_property<vec3>("v:point");
	for (auto v : cloud->vertices())
		std::cout << v.idx() << ", xyz: " << points[v] << ", color: " << colors[v] << std::endl;