{
"cells": [
{
"cell_type": "markdown",
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"collapsed": true,
"tags": [
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"I have had two simple raspberry pi weather stations running for a while now.\n",
"\n",
"Both have pressure, temperature and humidity sensors.\n",
"\n",
"One I have in the *carefully controlled environment* of my study, the\n",
"other is hanging out of the window.\n",
"\n",
"The study one is known as *pijessie* as it started life as a Raspberry\n",
"Pi running the Jessie version of Raspbian.\n",
"\n",
"The outside station is known as *kittycam* as I intend at some point\n",
"to attach a camera so I can watch our cat come and go.\n",
"\n",
"For a while I have been noticing that the pressure values have been\n",
"quite a way apart. The software I am includes a conversion to\n",
"altitude and I find these numbers more natural for me to think about.\n",
"\n",
"The altitude conversion assumes the pressure at sea level is 1023.25\n",
"hPa, which is the mean pressure at sea level.\n",
"\n",
"When the pressure is higher than this the altitude comes out below sea\n",
"level, when pressure is lower than this above sea level.\n",
"\n",
"As always, Wikipedia has good information on this:\n",
"https://en.wikipedia.org/wiki/Atmospheric_pressure\n",
"\n",
"For a while I had been noticing the two sensors giving values\n",
"differing by about 10 metres altitude.\n",
"\n",
"I had put this down to the sensors not being calibrated accurately,\n",
"but also noticed that kittycam was more prone to weird glitches.\n",
"\n",
"Now the glitches I put down to the fact I have one process collecting\n",
"data every minute and another process creating a display on my laptop\n",
"so I can glance over and see what the weather is doing. The latter\n",
"was just polling the sensor every 10 minutes.\n",
"\n",
"The code does not do anything smart like get a lock and my guess was\n",
"that the two processes were occasionally trampling on each other's feet.\n",
"\n",
"Long story short, I decided to take a closer look."
]
},
{
"cell_type": "code",
"execution_count": 34,
"metadata": {
"collapsed": false,
"tags": [
"worksheet-0"
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},
"outputs": [],
"source": [
"# Tell matplotlib to plot in line\n",
"%matplotlib inline\n",
"\n",
"import datetime\n",
"\n",
"# import pandas\n",
"import pandas\n",
"\n",
"# seaborn magically adds a layer of goodness on top of Matplotlib\n",
"# mostly this is just changing matplotlib defaults, but it does also\n",
"# provide some higher level plotting methods.\n",
"import seaborn\n",
"\n",
"# Tell seaborn to set things up\n",
"seaborn.set()\n"
]
},
{
"cell_type": "code",
"execution_count": 35,
"metadata": {
"collapsed": false,
"tags": [
"worksheet-0"
]
},
"outputs": [],
"source": [
"# input files: the data from the two sensors\n",
"infiles = [\"../files/kittycam_weather.csv\", \"../files/pijessie_weather.csv\"]\n"
]
},
{
"cell_type": "code",
"execution_count": 36,
"metadata": {
"collapsed": false,
"tags": [
"worksheet-0"
]
},
"outputs": [],
"source": [
"# Read the data\n",
"\n",
"data = []\n",
"\n",
"for infile in infiles:\n",
" data.append(pandas.read_csv(infile, index_col='date', parse_dates=['date']))\n"
]
},
{
"cell_type": "code",
"execution_count": 37,
"metadata": {
"collapsed": false,
"tags": [
"worksheet-0"
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},
"outputs": [
{
"data": {
"text/html": [
"\n",
"
\n",
" \n",
" \n",
" | \n",
" temp | \n",
" pressure | \n",
" altitude | \n",
" sealevel_pressure | \n",
" humidity | \n",
" temp_dht | \n",
"
\n",
" \n",
" \n",
" \n",
" | count | \n",
" 42768.000000 | \n",
" 42768.000000 | \n",
" 42768.000000 | \n",
" 42768.000000 | \n",
" 42764.000000 | \n",
" 42764.000000 | \n",
"
\n",
" \n",
" | mean | \n",
" 28.114357 | \n",
" 101385.375842 | \n",
" -5.068642 | \n",
" 101387.094487 | \n",
" 76.806599 | \n",
" 27.730374 | \n",
"
\n",
" \n",
" | std | \n",
" 2.205370 | \n",
" 430.276252 | \n",
" 36.334073 | \n",
" 409.738250 | \n",
" 8.512122 | \n",
" 2.068583 | \n",
"
\n",
" \n",
" | min | \n",
" 22.800000 | \n",
" 56117.000000 | \n",
" -1314.018026 | \n",
" 67136.000000 | \n",
" 29.500000 | \n",
" 22.299999 | \n",
"
\n",
" \n",
" | 25% | \n",
" 26.500000 | \n",
" 101141.750000 | \n",
" -26.939647 | \n",
" 101142.000000 | \n",
" 71.599998 | \n",
" 26.200001 | \n",
"
\n",
" \n",
" | 50% | \n",
" 27.700000 | \n",
" 101411.000000 | \n",
" -7.157439 | \n",
" 101412.000000 | \n",
" 77.099998 | \n",
" 27.400000 | \n",
"
\n",
" \n",
" | 75% | \n",
" 29.900000 | \n",
" 101648.000000 | \n",
" 15.246750 | \n",
" 101649.000000 | \n",
" 83.500000 | \n",
" 29.299999 | \n",
"
\n",
" \n",
" | max | \n",
" 43.200000 | \n",
" 102242.000000 | \n",
" 3397.334521 | \n",
" 118353.000000 | \n",
" 94.300003 | \n",
" 47.099998 | \n",
"
\n",
" \n",
"
\n",
"
\n",
"
\n",
" \n",
" \n",
" | \n",
" temp | \n",
" pressure | \n",
" altitude | \n",
" sealevel_pressure | \n",
" humidity | \n",
" temp_dht | \n",
"
\n",
" \n",
" \n",
" \n",
" | count | \n",
" 42768.000000 | \n",
" 42768.000000 | \n",
" 42768.000000 | \n",
" 42768.000000 | \n",
" 42764.000000 | \n",
" 42764.000000 | \n",
"
\n",
" \n",
" | mean | \n",
" 28.114357 | \n",
" 101385.375842 | \n",
" -5.068642 | \n",
" 101387.094487 | \n",
" 76.806599 | \n",
" 27.730374 | \n",
"
\n",
" \n",
" | std | \n",
" 2.205370 | \n",
" 430.276252 | \n",
" 36.334073 | \n",
" 409.738250 | \n",
" 8.512122 | \n",
" 2.068583 | \n",
"
\n",
" \n",
" | min | \n",
" 22.800000 | \n",
" 56117.000000 | \n",
" -1314.018026 | \n",
" 67136.000000 | \n",
" 29.500000 | \n",
" 22.299999 | \n",
"
\n",
" \n",
" | 25% | \n",
" 26.500000 | \n",
" 101141.750000 | \n",
" -26.939647 | \n",
" 101142.000000 | \n",
" 71.599998 | \n",
" 26.200001 | \n",
"
\n",
" \n",
" | 50% | \n",
" 27.700000 | \n",
" 101411.000000 | \n",
" -7.157439 | \n",
" 101412.000000 | \n",
" 77.099998 | \n",
" 27.400000 | \n",
"
\n",
" \n",
" | 75% | \n",
" 29.900000 | \n",
" 101648.000000 | \n",
" 15.246750 | \n",
" 101649.000000 | \n",
" 83.500000 | \n",
" 29.299999 | \n",
"
\n",
" \n",
" | max | \n",
" 43.200000 | \n",
" 102242.000000 | \n",
" 3397.334521 | \n",
" 118353.000000 | \n",
" 94.300003 | \n",
" 47.099998 | \n",
"
\n",
" \n",
"
\n",
"