怎样确定Openlayers中Proj4js地图投影参数

在Openlayers中使用非内置的坐标系时，需要设置投影参数并注册该投影。如下代码给出了怎样使用EPSG：21781 。示例代码出处
import Map from 'ol/Map';
import View from 'ol/View';
import proj4 from 'proj4';
import {register} from 'ol/proj/proj4';
import {get as getProjection} from 'ol/proj';

// To use other projections, you have to register the projection in OpenLayers.
// This can easily be done with [http://proj4js.org/](proj4)
//
// By default OpenLayers does n

怎样确定Openlayers中Proj4js地图投影参数最先出现在Python成神之路。