Garden GPS

I dropped my prototype Pi out into the garden with the GPS installed.  It’s running the code from the previous post.

Stationary GPS

Stationary GPS

Here’s what I got:

Outdoor GPS

Outdoor GPS

This is much more like what I was expecting.  The core is < ±5m from the origin – the top right area is the path as I returned the kit back into the office.  However, there’s still something wrong: it’s about 10m north to the back door, and yet it shows 30m on the ‘map’ based upon the change in latitude as I walk north, and the radius of the earth.  The scale here seems wrong yet it comes directly from this equirectangular approximation:

dx = (lon - base_lon) * math.cos((lat + base_lat) / 2) * R
dy = (lat - base_lat) * R

Throughout this test where the core is stable, the receiver was locked on to 7 – 10 satellites.  On the walk back inside, this reduces to 6 or fewer so that may explain it.  Next step is to include the accuracy measurement from the receiver to ultimately apply a bias for merging these values with the double integrated accelerometer distances.

P.S. Ignore all the wires, they are for URF and LEDDAR testing; the GPS is connected via a black USB cable.

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