为什么我无法将经纬网添加到极地立体地图中？(开放层 4)

Question

我正在 OpenLayers 4 中使用投影 EPSG：32661 绘制地图

这是JavaScript，它针对页面上的 #mapdiv：

proj4.defs('EPSG:32661', '+proj=stere +lat_0=90 +lon_0=0 +k=1 +x_0=0 +y_0=0 
+a=3396190 +b=3376200 +units=m +no_defs');
var north_stereo = ol.proj.get('EPSG:32661');
north_stereo.setExtent([-2357032, -2357032, 2357032, 2357032]);
var npoleURL = "https://planetarymaps.usgs.gov/cgi-bin/mapserv? 
map=/maps/mars/mars_npole.map";
var np = new ol.layer.Tile({
title: 'North Pole',
source: new ol.source.TileWMS({
url: npoleURL,
params: {LAYERS: 'MOLA_color_north'}
}),
projection: north_stereo,
});
var map = new ol.Map({
layers: [
np
],
target: 'map',
view: new ol.View({
projection: north_stereo,
center: [0, 0],
zoom: 4
})
});
var graticule = new ol.Graticule({
strokeStyle: new ol.style.Stroke({
color: 'rgba(0,0,0,0.8)',
width: 1,
}),
});
graticule.setMap(map);

这个代码笔演示了我遇到的问题。注释掉最后一行(即将经纬网附加到贴图的线(会导致贴图正常渲染。运行带有该行的代码会导致以下错误：

Uncaught TypeError: Cannot read property '0' of null
at Object.ol.extent.applyTransform (ol-debug.js:4719)
at Object.ol.proj.transformExtent (ol-debug.js:6268)
at ol.Graticule.updateProjectionInfo_ (ol-debug.js:57921)
at ol.Graticule.handlePostCompose_ (ol-debug.js:57876)
at ol.Map.boundListener (ol-debug.js:7277)
at ol.Map.ol.events.EventTarget.dispatchEvent (ol-debug.js:7697)
at ol.renderer.canvas.Map.dispatchComposeEvent_ (ol-debug.js:26392)
at ol.renderer.canvas.Map.renderFrame (ol-debug.js:26480)
at ol.Map.ol.PluggableMap.renderFrame_ (ol-debug.js:18709)
at ol.Map.<anonymous> (ol-debug.js:17624)

据我了解，proj4 会自动生成转换函数。变换点或要素图层已经成功，所以据我所知，经纬网是唯一造成麻烦的东西。

Answer 1

该错误是由于没有定义 worldExtent 而导致的，设置此选项应该可以解决问题

north_stereo.setWorldExtent([...]);