The GPS works by having transmitters send out their coordinates and time, the time is used to work out the distance from the transmitter, and trigonometry is used along with the data from a few transmitters to find your location.
The problem is that the coordinates used don't work on a FE (longitude, latitude and height don't fit with a flat earth), so any gsp device shouldn't work, as they are based of math for a sphere.
I hate to break it to you, but provided the transmitters send their true location, then the GPS system will work, there are plenty of DGPS systems out there that do just that.
DPGS systems work with satellite data. But yeah, there are ground based positioning systems - however they cannot calculate altitude, which the GPS does.
Have you ever heard of Altimeter Sensors - MEMS
Nice chips, I use the accelerometer MEMS in an instrument I manufacture. But that has nothing to do with the topic under discussion.
The DGPS ground based GPS transmitters, are mostly used for things like precision farming applications, where sub centimeter accuracy is required for seeding etc. But they still use the satellite systems as the baseline to which the differential is added.
I used an accelerometer for a rifle shot counter once.
I'm not a farmer, so I know little about using GPS for that purpose. However, I do know that the WMM, World Magnetic Model, is used for many things that seems to me could mimic what GPS is supposed to be doing.
The World Magnetic Model - UsesNavigation
Compasses have been used for several thousand years to determine direction. They point in the direction of magnetic force at the user’s location, and the direction it points is, more often than not, in a different direction than geographic north (toward the North Pole), a more precise direction is achieved by knowing the angle between them (magnetic declination). However, declination changes with location and time, and a geomagnetic model is often used to correct for it. Since the changes in geomagnetic fields are difficult to predict, timely model updates (every 5 years for the WMM) are required for navigational accuracy. The WMM satisfies all these criteria and is therefore widely used in navigation. Examples include, but are not limited to, ships, aircraft and submarines. Magnetometer based attitude (roll and pitch) control is commonly used in aircraft and satellites.
GPS
Why do we need magnetic navigation when Global Position System (GPS) is readily available? GPS provides precise point location but only measures travel direction when in constant motion. A GPS receiver must collect several sets of latitude and longitude pairs to obtain direction. In addition, GPS signals may become blocked due to obstructions, adverse terrestrial and space weather, ionospheric conditions or being underwater or underground. Hence, compasses complement GPS receivers to attain precise and immediate navigational headings for air, ground, and water-based systems. Electronic compasses and the WMM commonly co-exist in GPS receivers.
Antennas and Solar Panels
Antennas (e.g. satellite dish television) and solar panels often need to be precisely oriented for maximum performance. The WMM’s declination information for specific locations is often employed by companies to orient their products correctly.
Consumer Electronics
While the traditional use of the WMM is for navigation, it is now acquiring new utilities in consumer electronic devices with built-in digital compasses. Many of the new generations of smart phones and digital cameras take advantage of the WMM to estimate bearing. The availability of low-cost, small, and energy efficient electronic compasses allow for magnetic direction in portable electronics to be common place. This new user group will significantly increase the demand for WMM models in the near future. NGDC has developed an application called CrowdMag that allows users to collect their own magnetic field data using the magnetometers in their phone. This app sends data anonymously back to NOAA so it can be used to help validate and expand future magnetic models.
Mineral Exploration
Airborne and marine magnetic surveys are used by oil and mineral exploration companies to detect magnetic signals from the Earth’s crust. These small amplitude signals (typically 100s of nT), must be separated from the large main magnetic field (typically 20,000 to 60,000 nT). Geomagnetic models are used by companies to extract these small magnetic signals from the survey records. A new application is the use of geomagnetic models for directional drilling. Oil wells are often drilled horizontally from a conveniently located platform. An electronic compass located behind the drill head (bit) provides the engineers with accurate orientation of the bit.