1、参数与大小写无关，与顺序无关
2、通过getcapabilities发现getmap参数值支持的值
getcapabilities接口
http://meng/arcgis/services/testWMS/MapServer/WMSServer?
version=1.1.3&
request=GetCapabilities&
service=WMS
getmap接口
http://meng/arcgis/services/testWMS/MapServer/WMSServer?
version=1.3.0&
request=getmap&
layers=0& //图层序号而不是图层名
styles=population&
crs=4326&
bbox=105.274168,24.840616,117.736007,43.149934&
width=300&height=300&
format=image/gif //还有image/jpeg，通过arcgis server发布image service再发布成wms不支持image/gif格式
http://meng/arcgis/services/testimageservice/ImageServer/WMSServer?
version=1.3.0&
request=getmap&
layers=0&
styles=population&
crs=4326&
bbox=106.905538,39.630034,106.908181,39.631605&
width=300&height=300&
format=image/jpeg
http://meng/arcgis/services/imageWMS/MapServer/WMSServer?version=1.3.0&
request=getmap
&layers=0&
styles=population&
crs=4326&
bbox=106.811223,39.660308,106.817361,39.665052&
width=1200&height=1200&
format=image/gif