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我正在读取一个用于转换一个空间模型 (.gml) 的 js 文件。从一个特定的投影到另一个。如下代码中的":::"是什么意思?
_getTransformation(projectionFrom, projectionTo) {
let cacheKey = `${projectionFrom}:::${projectionTo}`;
if (!this.transformations[cacheKey]) {
let from = this._getProjection(projectionFrom);
let to = this._getProjection(projectionTo);
this.transformations[cacheKey] = proj4(from, to);
}
return this.transformations[cacheKey];
}