Spline Mesh Generator Research:

Some research would done on spline mesh generation.  

Unity tutorials define how spline mesh generated under the local spline and procedural geometry.  

The idea is similar to rendering a plane, it uses looping to generate a plane to form the ideal mesh and get reference of the vertex to run the Bezier curve calculation so it allow editor to drag and edit the spline from vertex position.

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This tutorial also got a similar idea, using Bezier curve calculation to get a vertex position and generate plane which form a mesh in procedural geometry. (https://youtu.be/o9RK6O2kOKo)

This tutorial does the same things on procedural geometry, instead it references spline tool from Unity package than script the spline from beginning. This will benefit the designer from accessing it and removing the spline tools in the package.

https://youtu.be/o9RK6O2kOKo)

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Debug sphere and line show resolution, and that's control the accurate of mesh generation on spline.  

Using the concept of Bezier curve in spline, the more resolution you have on the spline will render a smoother mesh.