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Topic: Autonomous Lawn Mower Navigation (Read 3 times) previous topic - next topic

johnwasser


Don't you need a surveyed point for the GPS to compare with to do differential?

You should only need a surveyed position if you want absolute coordinates. If you just want relative coordinates ("Where am I relative to the lawn boundary?") I think you just need a fixed location that both agree on. I would think that once both units have current ephemeris data they would agree on where they are.

If the base station is going to be in the same place each time you could calculate a long-term median position to use as the 'known' position.
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Khamey

johnwasser,

could you give a short explanation of the process you are describing.

Do we put the GPS units in the same location until they agree on a coordinate then start doing calculations? Or are we surveying for a set time until they have a good average location and then doing locations. Things are clearing up and we are doing a test today. Your advice is very helpful.

johnwasser

RTK (Realtime Kinematics) is another way to get accurate positioning from a GPS.  It takes more computer power than an Arduino can supply but a Beagle Board (or maybe a Raspberry Pi) can run it:

http://blog.makezine.com/2009/11/12/diy-real-time-kinematic-gps/
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michinyon

I don't think you can do "differential GPS"  just with two regular GPS modules.    You need a special device
which is in the thousand dollar ballpark  rather than the $50 ballpark.

I have done a bunch of experiments with two regular GPS modules to see if I got a more precise location
from them,  and the answer seems to me, to be no.   You do get some situations where one has a fix
and the other doesn't have a fix,   but in terms of precision,  not much improvement over the normal
position distribution noise.

jd.steinberger

Perhaps you could use one of these to cover the differential aspect.

https://www.sparkfun.com/products/10724

I would imagine with some basic calculus programming you could at least know fairly accurately your relationship
with your starting point or any other via you have exact coordinates of.

I read quite extensively about this IMU until I realized the accelerometer wasn't accurate enough for my project.  Seems like a pretty good product.

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