使用谷歌地图时，将GPS坐标映射到屏幕位置的好算法是什么？

I need an algorithm that will convert a GPS coordinate to a screen location on a displayed google map. I would think this would be simple- get the coordinates for the four corners of the displayed map, find the differential and create a scaling factor for a pixel location on the screen. Is this correct or am I missing something. I'm know this has been done ad nauseum but I am hoping I can hear from someone who has implemented it successfully or has a resource for implementing it. I need an algorithm that will convert a GPS coo