Well-placed labels can be the difference between a sloppy map and a beautiful one. Labels need to clearly identify features without obscuring the map.
好的标注位置可以作为潦草的地图和漂亮的地图之间的区别。标签需要清晰地识别要素而不模糊地图。
The normal requirements for map labelling are to place labels as clearly as possible without any overlap. Regular maps just need to avoid label overlap for a single, fixed zoom level and rotation.
地图标注的正常要求是尽可能清晰地放置标签，而不需要重叠。正常地图只需要对一个单一的固定缩放级别和旋转来避免标签重叠。
Good label placement is a hard problem that we solve for Mapbox GL. We need our label placements to work at any zoom and any rotation. We need labels placements to be continuous, so that labels don’t jump around when zooming or rotating. We need labels to be seamless across tiles. We need to support changing font sizes as you zoom. And it all needs to be fast.
好的标注安置是我们解决的一个难题。我们需要我们的标签放置在任何缩放和任何旋转中都能正常展示。我们需要标注安置是渐进型的，这样标签不至于在旋转、缩放时跳来跳去。我们需要标注在瓦片上上无缝地连接。当你缩放时，我们需要支持更改字体大小。而且一切都需要快速。
Placement needs to support both horizontal labels, as well as curved labels which follow a line. Both types of labels need to behave smoothly when zooming and rotating. Labels can never overlap, even when rotating. Horizontal labels stay horizontal and curved labels rotate with the map. Labels are flipped to avoid being drawn upside down and curved labels smoothly slide along roads.
安置需要同时支持水平文字标注和沿着一条曲线弯曲的标注。两种类型的标签都需要在缩放和旋转时表现得很平滑。标签永远不能重叠，即使旋转时也不能重叠。水平标签保持水平且曲线标签随着地图旋转。文本标注会被翻转以避免被渲染成字头向下（文字倒置）的情况，弯曲的标签沿着道路平滑滑动。
There is plenty of academic research on label placement, but most of this applies to maps with fixed rotation and with separate zoom levels. Dynamic maps with continuous zooming, panning, and rotation need a completely different approach. Our implementation expands on a paper by Been and Yap that establishes four ideal requirements for continuous and interactive labelling:
标签安置方面的学术研究很多，但大部分都适用于固定旋转和分立的缩放级别的地图。具有连续缩放、平移和旋转的动态地图需要完全不同的安置方法。我们的实现扩展了由Been 和 Yap编写的论文，该论文为连续和交互式标签确立了四个理想要求：
Labels should not disappear when zooming in or appear when zooming out.
Labels should not disappear or appear when panning except when sliding out of view.
Labels should not jump around, but instead should be anchored.
Label placement should be deterministic, no matter how you got to the current view.
标签不应该在放大时消失，在缩小时出现。
标签不应该在平移时消失或出现，除非滑出视图。
标签不应该跳来跳去，而是应该被锚定。
标签的位置应该是确定的，无论你怎么到当前视图。
The paper provides guidance on implementing this for horizontal labels, but we go further by supporting rotation and curved labels.
该论文为水平标注的实现提供了指导，但是我们通过支持旋转和弯曲标签来更进一步完善文本安置。
Our implementation has two steps:
Preprocessing
Rendering
我们的实现有两个步骤：
预处理
渲染
The rendering step needs to be fast so that Mapbox GL can rerender the entire map every frame for smooth interaction. Most of the placement work happens in the preprocessing step:
Generate anchor points for each label.
Calculate the positions of individual glyphs relative to the anchors.
Calculate the zoom levels at which the labels and glyphs can be shown without overlap.
Calculate the rotation range in which the label can be shown.
渲染步骤需要足够快以便为了mapbox gl 能够在每一帧中都能重新渲染整个地图以达到顺滑的交互效果。大多数的安置个工作发生在预处理的步骤中：
为每个标签生成锚点。
计算各个字形相对于锚点的位置。
计算该标签和符号可以没有重叠显示的缩放级别。
计算可以显示标签的旋转范围。
Generating anchor points
Each label has an anchor. An anchor is the point at which a label is positioned when zooming or rotating.
每一个标签都有一个锚点，锚点是指缩放活旋转时被定位位置的点。
Labels for point features have a single anchor, the point.
对于点要素的标签只有一个锚点，就是这个点本身。