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Setting the Hand Controller Location on Boot

A project log for Raspberry Pi Driven Telescope Mount

full telescope control over WiFi using INDI on a RPi Zero W

Dane GardnerDane Gardner 11/26/2018 at 00:160 Comments

After using network time protocol (NTP) to set the hand controller's time on start, I was lamenting that I still had to set the location manually.  I could easily use the same script as a starting point to set the location using my network's IP address geolocation, so why don't I?

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There are plenty of free services on the web to get an IP address' latitude and longitude.  I chose `ipinfo.io` because it allows a few requests per day without a license, and it was easiest to extract the location using a CLI JSON parser called `jq`.  At the command line you can get your location like this:

$ curl -s ipinfo.io | jq -r '.loc'
47.6205,-122.3493

According to the Celestron protocol documentation for location setting, we need it in a degrees/minutes/seconds format with an extra byte for hemisphere.

The format of the location commands is: ABCDEFGH, where:
A is the number of degrees of latitude.
B is the number of minutes of latitude.
C is the number of seconds of latitude.
D is 0 for north and 1 for south.
E is the number of degrees of longitude.
F is the number of minutes of longitude.
G is the number of seconds of longitude.
H is 0 for east and 1 for west.

I was disappointed that I couldn't find any easy way of converting floating point degrees to DMS format at the command line in Raspbian.  As a rule I don't do math in Bash, so I had to write my own in Python.

def dms(deg):
    m = (abs(deg) - int(abs(deg))) * 60.0
    s = (abs(m) - int(abs(m))) * 60.0
    return (int(deg), int(m), int(s))

def celestron(deg):
    c = dms(deg)
    return "{0:d} {1:d} {2:d} {3:d}".format(abs(c[0]), c[1], c[2], 0 if(c[0] >= 0) else 1)

print "{0} {1}".format(celestron(lat), celestron(lon))

Combining these two concepts with the previous script for setting the time, I came up with a couple scripts, and kicked them off with the `/etc/rc.local` script so it runs at boot.  This works surprisingly well from my home network, which is a little scary from a privacy perspective.

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