google.maps.Projection 类的作用是什么？

发布于 2024-11-02 22:12:39 字数 1339 浏览 5 评论 0原文

最近，我发现在屏幕上的 LatLngs 和像素坐标之间进行转换的困难方法是我不应该使用 Projection 类可以通过 Map.getProjection 轻松访问，但我应该使用 MapCanvasProjection 只能访问的类通过OverlayView。

如果您正在使用自定义叠加层，则后者非常好用且方便，但如果您没有使用自定义叠加层，则访问 MapCanvasProjection 会非常痛苦。到目前为止，我已经通过向 Map 类添加一个方法为自己解决了这个问题，该方法使我可以轻松访问所需的投影类：

google.maps.Map.prototype.getCanvasProjection = function() {
  if (!this.projectionOverlay) {
    this.projectionOverlay = new google.maps.OverlayView();
    this.projectionOverlay.onAdd = function(){};
    this.projectionOverlay.onRemove = function(){};
    this.projectionOverlay.draw = function(){};
    this.projectionOverlay.setMap(this);
  }
  return this.projectionOverlay.getProjection();
};

这一切看起来像是一个大技巧，可以做一些本应微不足道的事情。这让我更加想知道 google.maps.Projection 类做什么？当我阅读文档时，在我看来， Projection.fromLatLngToPoint 与 MapCanvasProjection.fromLatLngToContainerPixel 执行相同的操作，但事实并非如此。我很困惑。

原文

Recently I found out the hard way that to convert between LatLngs and pixel coordinates on screen I shouldn't use the Projection class that is easily accessed through Map.getProjection, but instead I should use the MapCanvasProjection class that can only be accessed through OverlayView.

The latter is nice and handy if you are working with a custom overlay, but if you're not, it's really painful to get access to the MapCanvasProjection. So far I have solved this problem for myself by adding a method to the Map class that will give me easy access to the desired projection class:

google.maps.Map.prototype.getCanvasProjection = function() {
  if (!this.projectionOverlay) {
    this.projectionOverlay = new google.maps.OverlayView();
    this.projectionOverlay.onAdd = function(){};
    this.projectionOverlay.onRemove = function(){};
    this.projectionOverlay.draw = function(){};
    this.projectionOverlay.setMap(this);
  }
  return this.projectionOverlay.getProjection();
};

This all looks like a big hack to do something that should be trivial. And it ever more makes me wonder what does the google.maps.Projection class do? When I read the documentation it seems to me that Projection.fromLatLngToPoint does the same thing as MapCanvasProjection.fromLatLngToContainerPixel, but it does not. I'm puzzled.

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