Negative Altitude value in Android

Question

I'm getting negative Altitude value even when I'm on 6 storey building . I initially thought my code was wrong, so I've downloaded couple of apps from play store. Even it is showing negative value.

My location is

Chennai, Tamilnadu, India

Answer 1

Your device is getting poor GPS results for some reason, possibly due to hardware limitations or firmware bugs. Contact the device manufacturer for assistance.

Answer 2

Have you tried looking at this? I'm not an expert on GPS, but the two points in the answer here are likely to be the issue. Android: How to get accurate altitude?

Answer 3

I've just googled around a little bit and this is what I've found about Chennai:

Elevation 6 m (20 ft)

The first thing that pops in my mind is that this is average elevation, which probably means that there are some parts of the city way above that, and also some parts that are below the sea level, even by 10-15m (which is roughly the height of the 6th floor).

This, combined with high margin for error of GPS altitude measurement (+/- 15m), might have resulted in your seeing the negative altitude.

I might be wrong though, this is just my initial idea. You can test it by climbing a nearby hills or mountains, such as [according to google] Pallavaram Mountain.

Answer 4

GPS readings of altitudes aren't always accurate and have an error within about +/- 15 meters (50 feet) 95% of the time. GPS depends on clear and unobstructed view or it cannot make accurate range measurements to the satellites and hence the error. So I would say to take the GPS readings with a grain of salt.

I am not sure what you plan to use the data for , but I would suggest you to normalize the readings you get over a period of time and use it.

Here's the source

Usually map data provides the average altitude levels of a given region, you can perhaps account that as a base value and compute relatively accurate altitudes.