DGPS Mindstorms API

dgps
#1

Hello from New Zealand

I have looked through the forum and various places online but found nothing. Is there an API/instructions for how to use the navigation aspects of the dGPS with Brickpi3 and in python? I’m building a robot to track over a list of waypoints and would prefer to use the inbuilt methods rather than write my own. Particularly around the:

"DGPS_CMD_DIST   = 0x08      # Fetch distance to destination" and,
"DGPS_CMD_ANGD   = 0x09      # Fetch angle to destination"

functions of the dGPS. How do you set the destination and then how do you call to find the distance and direction?

(I’m guessing the distance/direction retrieval is BP.transact_i2c(GPS_PORT, DGPS_I2C_ADDR, [DGPS_CMD_DIST], 3) then value = BP.get_sensor(GPS_PORT) but thought I’d ask as well)

Thanks

#2

Hello @markacereid from the US! It’s been a long time since I’ve looked at the dGPS code, but I’ll give it a shot!

The registry for setting the destinations are here:

DGPS_CMD_SLAT   = 0x0B      # Set latitude of destination 
DGPS_CMD_SLONG = 0x0C       # Set longitude of destination

You would use these to set the destination you’re headed. So you could use the onboard calculator, but you would probably be better served to calculate it in Python on the Raspberry Pi (this would be faster too!). There’s a great stack overflow answer on this here. The fastest (and easiest to troubleshoot) implementation would be to use this code (copy and paste from so):

from math import sin, cos, sqrt, atan2, radians

# approximate radius of earth in km
R = 6373.0

lat1 = radians(52.2296756)
lon1 = radians(21.0122287)
lat2 = radians(52.406374)
lon2 = radians(16.9251681)

dlon = lon2 - lon1
dlat = lat2 - lat1

a = sin(dlat / 2)**2 + cos(lat1) * cos(lat2) * sin(dlon / 2)**2
c = 2 * atan2(sqrt(a), sqrt(1 - a))

distance = R * c

print("Result:", distance)
print("Should be:", 278.546, "km")

Does this help?

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