Simplify a TIN Surface in BricsCAD

Quick answer: TIN Simplify divides a surface’s points into square cells and works through them one by one, excluding nearby points whose elevation difference exceeds a value you set. A larger cell size means fewer points and lower accuracy; a smaller cell size preserves more accuracy in the simplified surface.

How the Algorithm Works

1. Points are divided into square cells, one point per cell.
2. The first point is taken from the first cell, following the order points appear in the input point file or point cloud.
3. Around that point, every adjacent point within a given radius, including points in neighbouring cells, is checked against the elevation difference (∆h) you’ve set.
4. Any adjacent point with a higher ∆h than your specified value is excluded.
5. The process repeats for the next point in the first cell, then moves to the adjacent cell in the x-coordinate direction, continuing cell by cell until it reaches the last one.

The Default Radius Value

BricsCAD proposes a starting value for the Radius for simplification step automatically: it calculates the bounding box of your input points, takes whichever of its two dimensions (length or width) is larger, and works out 0.5% of that value, rounded, as the suggested radius shown at the Command line.

The Accuracy Tradeoff

A larger cell size (a bigger radius) means lower accuracy in the resulting TIN surface, since more points get excluded. For a more accurate simplified network, use a smaller cell size instead.

Frequently Asked Questions

How does BricsCAD decide which points to keep when simplifying? It works cell by cell, checking each point’s neighbours within a set radius and excluding any whose elevation difference from that point exceeds your specified value.

Where does the default radius value come from? It’s calculated from the bounding box of your input points: 0.5% of whichever dimension, length or width, is larger.

Should I use a large or small cell size for the most accurate simplified surface? A smaller cell size gives greater accuracy. A larger cell size reduces the point count further but at the cost of accuracy.

Does the order points appear in the source file matter for simplification? Yes, the algorithm starts with the first point in the first cell based on the order points appear in the input point file or point cloud.