What is Horizontal Accuracy

Question

I am new bee in Unity3d and working on location app. I am enabling location on device and getting current location. I get few parameter in response which are Lat Long Altitude and Horizontal Accuracy. I know first three of them but don't know last one which is Horizontal Accuracy. I googled and get Apple Documentation Horizontal Accuracy. As far as my understanding it says that This is radius size around lat and long. If yes then i have following questions.

• what is the default value of Horizontal Accuracy because i am getting 10.
• Can we change this value(radius around lat and long)
• What is Vertical Accuracy, if exist.

Thanks in advance.

Solution

GPS is not pinpoint accurate. The nature of GPS data is that it is an ongoing estimation, and this estimation has a time-varying margin of error depending on conditions. For further background start with Basic Concept of GPS (Wikipedia).

In the most fundamental sense the accuracy is a result of GPS conditions for that device, location, and time, and is not directly controllable by the developer, at least not through any software mechanism. However, if you see the documentation for LocationService.Start() (Unity), you'll notice a desiredAccuracyInMeters value. This basically affects how long you must wait before there is an available value within that desired accuracy. A precise value will take more time to produce, while a coarse value may be available very quickly.

Horizontal Accuracy is a radius about a 2d point, implying that the true, unknown 2d location is somewhere within the circle formed by the given point as a center and the accuracy as a radius. Vertical Accuracy exists if you are given altitude information, is a 1d location, and similarly implies that the true, unknown altitude is somewhere within a region defined by the center (given altitude) and "radius" (given vertical accuracy).

Also see struct LocationInfo (Unity).