Divide by Zero error generating graphs

[Greeebs]

Hi all,

New weewx user here using a home brew weather station based on Arduino's and nRF24L01+ radios.

I wrote my own driver to accept packets on the nRF24L01 attached to the RPi and weewx is happily accepting my LOOP packets and producing reports every archiving period. I've also managed to import the last 18 months of weather data  I had collected prior to installing weewx. Until today, weewx has been going fantastically.

Today I encountered a weird issue which I've not found described elsewhere. I was getting a divide by zero error during graph generation and none of my graphs were being updated.

I had a period of 24+ hours where my humidity was stuck at 100%. As soon as it dropped to 99%, the error went away and all of my graphs were updated.

It turns out that if you specify only a maximum value for a graph, and have a period where the reading for the entire graph period was at that maximum, you get the divide by zero error.

Is this a known bug?

Here's the relevant section from the log:

Sep 25 06:26:19 hub-pi weewx[436]: reportengine: Caught unrecoverable exception in generator weewx.imagegenerator.ImageGenerator

Sep 25 06:26:19 hub-pi weewx[436]:         ****  float division by zero

Sep 25 06:26:19 hub-pi weewx[436]:         ****  Traceback (most recent call last):

Sep 25 06:26:19 hub-pi weewx[436]:         ****    File "/usr/share/weewx/weewx/reportengine.py", line 239, in run

Sep 25 06:26:19 hub-pi weewx[436]:         ****      obj.start()

Sep 25 06:26:19 hub-pi weewx[436]:         ****    File "/usr/share/weewx/weewx/reportengine.py", line 273, in start

Sep 25 06:26:19 hub-pi weewx[436]:         ****      self.run()

Sep 25 06:26:19 hub-pi weewx[436]:         ****    File "/usr/share/weewx/weewx/imagegenerator.py", line 32, in run

Sep 25 06:26:19 hub-pi weewx[436]:         ****      self.genImages(self.gen_ts)

Sep 25 06:26:19 hub-pi weewx[436]:         ****    File "/usr/share/weewx/weewx/imagegenerator.py", line 235, in genImages

Sep 25 06:26:19 hub-pi weewx[436]:         ****      image = plot.render()

Sep 25 06:26:19 hub-pi weewx[436]:         ****    File "/usr/share/weewx/weeplot/genplot.py", line 195, in render

Sep 25 06:26:19 hub-pi weewx[436]:         ****      sdraw = self._getScaledDraw(draw)

Sep 25 06:26:19 hub-pi weewx[436]:         ****    File "/usr/share/weewx/weeplot/genplot.py", line 222, in _getScaledDraw

Sep 25 06:26:19 hub-pi weewx[436]:         ****      ((self.xscale[0], self.yscale[0]), (self.xscale[1], self.yscale[1])))

Sep 25 06:26:19 hub-pi weewx[436]:         ****    File "/usr/share/weewx/weeplot/utilities.py", line 317, in __init__

Sep 25 06:26:19 hub-pi weewx[436]:         ****      self.yscale = -float(lri[1] - uli[1]) / float(urs[1] - lls[1])

Sep 25 06:26:19 hub-pi weewx[436]:         ****  ZeroDivisionError: float division by zero

Sep 25 06:26:19 hub-pi weewx[436]:         ****  Generator terminated

Sep 25 06:26:19 hub-pi weewx[436]: copygenerator: copied 0 files to /var/www/html/weewx

Here's the relevant section from the skin.conf:

        [[[dayhum]]]

            yscale = None, 100, None

            [[[[outHumidity]]]]

[Thomas Keffer]

I was able to reproduce this. I've created issue #344 to track.

Shouldn't be too hard to fix.

-tk

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[R Sparkes]

Excellent!

Much appreciated.

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[Thomas Keffer]

OK, replace your copy of weeplot/utilities.py with the attached.

Incidentally, good sleuthing when you figured out the problem! It made it easy to come up with the fix.

-tk

[R Sparkes]

Thanks for the quick turnaround, I've put that new version in place and will see how it goes.

[Greeebs]

Just like to confirm that after another period of 24+ hours of 100% humidity, I'm still getting graphs generated so this is now definitely fixed :)