# Efficient Spatial Anti-Aliasing Rendering for Line Joins on Vector Maps

## TL;DR

This paper introduces an efficient anti-aliasing algorithm for line joins in vector maps that improves visual realism and performance by replacing multiple triangles with just two, reducing memory and increasing frame rate.

## Contribution

The paper presents a novel algorithm that simplifies spatial anti-aliasing for line joins using only two triangles, enhancing realism and system efficiency.

## Key findings

- Achieves realistic anti-aliasing with fewer triangles.
- Reduces memory usage and increases rendering speed.
- Widely adopted in commercial Internet Maps.

## Abstract

The spatial anti-aliasing technique for line joins (intersections of the road segments) on vector maps is exclusively crucial to visual experience and system performance. Due to limitations of OpenGL API, one common practice to achieve the anti-aliased effect is splicing multiple triangles at varying scale levels to approximate the fan-shaped line joins. However, this approximation inevitably produces some unreality, and the system rendering performance is not optimal. To circumvent these drawbacks, in this paper, we propose a simple but efficient algorithm which uses only two triangles to substitute the multiple triangles approximation and then renders a realistic fan-shaped curve with alpha operation based on geometrical relation computing. Our experiment shows it has advantages of a realistic anti-aliasing effect, less memory cost, higher frame rate, and drawing line joins without overlapping rendering. Our proposed spatial anti-aliasing technique has been widely used in Internet Maps such as Tencent Mobile Maps and Tencent Automotive Maps.