adding inclinometer example

[FoamyGuy]

This adds an inclinometer example based on the code in the older PR referenced in issue #2. It's been tested successfully with lsm303_accel and mpu6050 and should work with any sensor that uses the same .acceleration property to expose accelerometer data.

Let me know if there is a different / better place for this example to live for eventual inclusion in a learn guide and if I should go ahead create similar PRs for the other sensor libraries that this example will work with.

[caternuson]

Code is functional. So comments are mainly code style suggestions.

[caternuson]

Consider switching to newer style .format string formatting instead of %.

Also maybe add more description of what the two values are? Something like this?

print("XZ angle = {:6.2}deg   YZ angle = {:6.2}deg".format(get_inclination(sensor)))

[FoamyGuy]

I like it, will make this change tonight.

[FoamyGuy]

I'm getting this error when I use this code as is.

TypeError: can't convert 'tuple' object to str implicitly

I've changed it to this which solves this tuple conversion error by making a variable and accessing the indexes individually. If there is some other syntax that allows it to work as a one liner I can use that but I'm not sure of how to do it. I also used float formatting because it showed exponential notation sometimes.

inclination = get_inclination(sensor)
print("XZ angle = {:6.2f}deg   YZ angle = {:6.2f}deg".format(inclination[0],inclination[1]))

[caternuson]

Ah, yah. My bad. I was just coding from the hip. The actual formatter syntax may be wrong too.

Try this:

print("XZ angle = {:6.2f}deg   YZ angle = {:6.2f}deg".format(*get_inclination(sensor)))

Added fs to the formatter and used the * trick to unpack the tuple. What do you think about splitting it into two lines?

angle_xz, angle_yz = get_inclination(sensor)
print("XZ angle = {:6.2f}deg   YZ angle = {:6.2f}deg".format(angle_xz, angle_yz))

[FoamyGuy]

Ah the asterisk does work. I like your two line version best. I've just pushed a change to that one.

[caternuson]

Could be shortened to something like

angle = degrees(atan2(y, x))
if angle < 0:
    angle += 360
return angle

[FoamyGuy]

Same here, will make this change tonight.

[caternuson]

With this approach you read the sensor twice. It probably happens so fast it's no big deal. But you could get rid of the two get_inclination_respect functions and have this one be something like:

x, y, z = _sensor.acceleration
return vector_2_degrees(x, z), vector_2_degrees(y, z)

and then both inclination computations would be done from the same sensor reading.

[FoamyGuy]

Thank you for pointing this out. Like you say it's so fast it usually doesn't matter but I have had the pleasure of debugging weirdness caused by making multiple reads like this getting different results on with other sensors, definitely should be storing it to a variable to reference from there instead. I will get this changed tonight as well.

[caternuson]

Cool. Looks good!