Speed of Design
Since we implemented a page look-up table, the start time for the drawing of the map is less than one second. This is a very good reaction time, because messages being sent by the GPS receiver are once every second. The position of the user is updated every ¼ second since it is running off timer0.
Storing the map to the DataFlash takes about 20 minutes because we are storing 15,000 bits of data. This needs to only be done once. So if we were to manufacture our design the device would come preload with the map information.
The location of the user on the campus map, given a latitude and longitude coordinate is accurate to several feet. To acquire the latitude and longitude of various locations around the Cornell Campus we used a GPS receiver the told the decimal minutes of these locations. Then we zoomed in to our maximum zoom level and read the pixel points that corresponded to our location on the map. We then plotted longitudes vs. the X-pixel and then the latitude vs. the Y-pixel. We then generated a linear equation that would give a pixel coordinate for a given latitude and longitude. This equation, in conjunction with the information transmitted by the GPS, determine the location of the user on the screen.
The only safety concern with our device is the power to the LCD. Our LCD uses a 24V power supply. This is equivalent to using 3 9V batteries. Because this voltage is pretty low, our device is very safe.
Since we are using a GPS simulator to send NMEA sentences to our device, there is no interference with other design projects
Since the map is preloaded before the user can interface with the device, our project is very user friendly. The user interface is a set of push buttons. So if you are able to push a buzzer you will be able to use our device.