CORS C ontinuous O peration R eference S ite real time processing, continuous absolute positioning ( X, Y, Z). realtime RTK distance between each station is usually less than 20 km. Trimble can be upto 50 km due to interference due to ionosphere and high sunspot activity, interference from mobile phone base stations, mobile base station cars only Trimble has an autoswitch competitor : Leica Spider, can only do manual switch output data frequency: up to 50 Hz military grade ( normally 5, 10 to 20 Hz) application: 國家陸態網. to detect minute land movement , due to eargththqqiiale eartjhquake. or 大陸板塊移動 seismic movement choke ring antenna - has high sensitivity against multi path interference