Something deeper must be going on. Please replace your copy of
/home/weewx/bin/weeplot/genplot.py with the attached. It has been
instrumented to give us more information about the error.

Run until weewxd (or wee_reports). Hopefully, the report will crash like
before. Post the resultant log.

-tk

On Thu, Jan 14, 2021 at 7:53 AM Tarmo <[email protected]> wrote:

> Hello, Tom!
>
> No less than or equal to zero values at min_interval.
>
> pi@pi3:/home/weewx/skins/Seasons $ grep yscale skin.conf
>     # plotting can be controlled using option 'yscale'. It is a 3-way
> tuple,
>     yscale = None, None, None
>             yscale = None, None, 0.5
>             yscale = None, None, 0.02
>             yscale = 0.0, 360.0, 45.0
> #            yscale = 0, 16, 1
>             yscale = 0.0, 100.0, 25.0
>             yscale = 0, None, 0.01
>             yscale = None, None, 0.5
>             yscale = None, None, 0.02
>             yscale = 0.0, 360.0, 45.0
> #            yscale = 0, 16, 1
>             yscale = 0.0, 100.0, 25.0
>             yscale = 0, None, 0.01
>             yscale = None, None, 0.5
>             yscale = None, None, 0.02
>             yscale = 0.0, 360.0, 45.0
> #            yscale = 0, 16, 1
>             yscale = 0.0, 100.0, 25.0
>             yscale = 0, None, 0.01
>             yscale = None, None, 0.5
>             yscale = None, None, 0.02
>             yscale = 0.0, 360.0, 45.0
> #            yscale = 0, 16, 1
>             yscale = 0.0, 100.0, 25.0
>             yscale = 0, None, 0.01
>
>
>
> On Thursday, January 14, 2021 at 5:11:12 PM UTC+2 [email protected] wrote:
>
>> Hello, Tarmo
>>
>> One of the images that you are trying to generate has an option y_scale
>> <http://www.weewx.com/docs/customizing.htm#Plot_scaling_options> with a
>> min_interval of zero, or less than zero.
>>
>> Look in the file /home/weewx/skins/Seasons/skin.conf for images that use
>> y_scale. They will look something like this:
>>
>>     yscale = 10, 20, -1
>>
>> or like this
>>
>>     yscale = 10, 20, 0
>>
>> The "10" and the "20" do not matter. It's the last number that we care
>> about. It cannot be less than or equal to zero.
>>
>> If you're having trouble, post the file skin.conf.
>>
>> -tk
>>
>> On Thu, Jan 14, 2021 at 3:37 AM Tarmo <[email protected]> wrote:
>>
>>> Hi,
>>>
>>> Please help with this:
>>>
>>> Jan 14 13:21:58 pi3 systemd[1]: Starting LSB: weewx weather system...
>>> Jan 14 13:21:59 pi3 weewx[1306] INFO __main__: Initializing weewx
>>> version 4.3.0b2
>>> Jan 14 13:21:59 pi3 weewx[1306] INFO __main__: Using Python 3.5.3
>>> (default, Nov 18 2020, 21:09:16) #012[GCC 6.3.0 20170516]
>>> Jan 14 13:21:59 pi3 weewx[1306] INFO __main__: Platform
>>> Linux-4.19.66-v7+-armv7l-with-debian-9.13
>>> Jan 14 13:21:59 pi3 weewx[1306] INFO __main__: Locale is 'en_GB.UTF-8'
>>> Jan 14 13:21:59 pi3 weewx[1306] INFO __main__: PID file is
>>> /var/run/weewx.pid
>>> Jan 14 13:21:59 pi3 weewx[1310] INFO __main__: Using configuration file
>>> /home/weewx/weewx.conf
>>> Jan 14 13:21:59 pi3 weewx[1310] INFO __main__: Debug is 0
>>> Jan 14 13:21:59 pi3 weewx[1310] INFO weewx.engine: Loading station type
>>> Vantage (weewx.drivers.vantage)
>>> Jan 14 13:21:59 pi3 weewx[1295]: Starting weewx weather system: weewx.
>>> Jan 14 13:21:59 pi3 systemd[1]: Started LSB: weewx weather system.
>>> Jan 14 13:21:59 pi3 weewx[1310] INFO weewx.engine: StdConvert target
>>> unit is 0x1
>>> Jan 14 13:21:59 pi3 weewx[1310] INFO weewx.engine: Archive will use data
>>> binding wx_binding
>>> Jan 14 13:21:59 pi3 weewx[1310] INFO weewx.engine: Record generation
>>> will be attempted in 'hardware'
>>> Jan 14 13:21:59 pi3 weewx[1310] INFO weewx.engine: Using archive
>>> interval of 300 seconds (specified by hardware)
>>> Jan 14 13:21:59 pi3 weewx[1310] INFO weewx.restx: StationRegistry:
>>> Station will be registered.
>>> Jan 14 13:21:59 pi3 weewx[1310] INFO user.mqtt: service version is 0.22
>>> Jan 14 13:21:59 pi3 weewx[1310] INFO user.mqtt: binding to loop
>>> Jan 14 13:21:59 pi3 weewx[1310] INFO user.mqtt: topic is weather
>>> Jan 14 13:21:59 pi3 weewx[1310] INFO user.mqtt: desired unit system is
>>> METRIC
>>> Jan 14 13:21:59 pi3 weewx[1310] INFO user.mqtt: data will be uploaded to
>>> mqtt://ilm:xxx@localhost:1883/
>>> Jan 14 13:21:59 pi3 weewx[1310] INFO weewx.restx: Wunderground-PWS: Data
>>> for station IHARJUMA19 will be posted
>>> Jan 14 13:21:59 pi3 weewx[1310] INFO user.windy: version is 0.7
>>> Jan 14 13:21:59 pi3 weewx[1310] INFO user.windy: Data will be uploaded
>>> to https://stations.windy.com/pws/update
>>> Jan 14 13:21:59 pi3 weewx[1310] INFO __main__: Starting up weewx version
>>> 4.3.0b2
>>> Jan 14 13:21:59 pi3 weewx[1310] INFO weewx.engine: Clock error is 0.06
>>> seconds (positive is fast)
>>> Jan 14 13:21:59 pi3 weewx[1310] INFO weewx.engine: Using binding
>>> 'wx_binding' to database 'weewx.sdb'
>>> Jan 14 13:21:59 pi3 weewx[1310] INFO weewx.manager: Starting backfill of
>>> daily summaries
>>> Jan 14 13:21:59 pi3 weewx[1310] INFO weewx.engine: Starting main packet
>>> loop.
>>> Jan 14 13:25:20 pi3 weewx[1310] INFO weewx.manager: Added record
>>> 2021-01-14 13:25:00 EET (1610623500) to database 'weewx.sdb'
>>> Jan 14 13:25:20 pi3 weewx[1310] INFO weewx.manager: Added record
>>> 2021-01-14 13:25:00 EET (1610623500) to daily summary in 'weewx.sdb'
>>> Jan 14 13:25:22 pi3 weewx[1310] INFO weewx.restx: Windy: Published
>>> record 2021-01-14 13:25:00 EET (1610623500)
>>> Jan 14 13:25:22 pi3 weewx[1310] INFO weewx.restx: StationRegistry:
>>> Published record 2021-01-14 13:25:00 EET (1610623500)
>>> Jan 14 13:25:22 pi3 weewx[1310] INFO weewx.restx: Wunderground-PWS:
>>> Published record 2021-01-14 13:25:00 EET (1610623500)
>>> Jan 14 13:27:00 pi3 weewx[1310] INFO weewx.cheetahgenerator: Generated
>>> 158 files for report SeasonsReport in 98.47 seconds
>>> Jan 14 13:27:06 pi3 weewx[1310] ERROR weewx.reportengine: Caught
>>> unrecoverable exception in generator 'weewx.imagegenerator.ImageGenerator'
>>> Jan 14 13:27:06 pi3 weewx[1310] ERROR weewx.reportengine: **** math
>>> domain error
>>> Jan 14 13:27:06 pi3 weewx[1310] ERROR weewx.reportengine: **** Traceback
>>> (most recent call last):
>>> Jan 14 13:27:06 pi3 weewx[1310] ERROR weewx.reportengine: **** File
>>> "/home/weewx/bin/weewx/reportengine.py", line 196, in run
>>> Jan 14 13:27:06 pi3 weewx[1310] ERROR weewx.reportengine: ****
>>> obj.start()
>>> Jan 14 13:27:06 pi3 weewx[1310] ERROR weewx.reportengine: **** File
>>> "/home/weewx/bin/weewx/reportengine.py", line 281, in start
>>> Jan 14 13:27:06 pi3 weewx[1310] ERROR weewx.reportengine: **** self.run()
>>> Jan 14 13:27:06 pi3 weewx[1310] ERROR weewx.reportengine: **** File
>>> "/home/weewx/bin/weewx/imagegenerator.py", line 41, in run
>>> Jan 14 13:27:06 pi3 weewx[1310] ERROR weewx.reportengine: ****
>>> self.genImages(self.gen_ts)
>>> Jan 14 13:27:06 pi3 weewx[1310] ERROR weewx.reportengine: **** File
>>> "/home/weewx/bin/weewx/imagegenerator.py", line 263, in genImages
>>> Jan 14 13:27:06 pi3 weewx[1310] ERROR weewx.reportengine: **** image =
>>> plot.render()
>>> Jan 14 13:27:06 pi3 weewx[1310] ERROR weewx.reportengine: **** File
>>> "/home/weewx/bin/weeplot/genplot.py", line 210, in render
>>> Jan 14 13:27:06 pi3 weewx[1310] ERROR weewx.reportengine: ****
>>> self._calcYScaling()
>>> Jan 14 13:27:06 pi3 weewx[1310] ERROR weewx.reportengine: **** File
>>> "/home/weewx/bin/weeplot/genplot.py", line 517, in _calcYScaling
>>> Jan 14 13:27:06 pi3 weewx[1310] ERROR weewx.reportengine: ****
>>> self.yscale = weeplot.utilities.scale(ymin, ymax, self.yscale,
>>> nsteps=self.y_nticks)
>>> Jan 14 13:27:06 pi3 weewx[1310] ERROR weewx.reportengine: **** File
>>> "/home/weewx/bin/weeplot/utilities.py", line 132, in scale
>>> Jan 14 13:27:06 pi3 weewx[1310] ERROR weewx.reportengine: **** mag =
>>> math.floor(math.log10(steps))
>>> Jan 14 13:27:06 pi3 weewx[1310] ERROR weewx.reportengine: ****
>>> ValueError: math domain error
>>> Jan 14 13:27:06 pi3 weewx[1310] ERROR weewx.reportengine: **** Generator
>>> terminated
>>> Jan 14 13:27:06 pi3 weewx[1310] INFO weewx.reportengine: Copied 15 files
>>> to /var/ramdisk/ilmajaam
>>> Jan 14 13:27:07 pi3 weewx[1310] INFO weeutil.rsyncupload: rsync'd 206
>>> files (865,386 bytes) in 0.95 seconds
>>>
>>> --
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>>> To view this discussion on the web visit
>>> https://groups.google.com/d/msgid/weewx-user/4a9fa165-a2d6-42ee-bd21-b592e83bac22n%40googlegroups.com
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>>> .
>>>
>> --
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> To view this discussion on the web visit
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> .
>

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#
#    Copyright (c) 2009-2019 Tom Keffer <[email protected]>
#
#    See the file LICENSE.txt for your full rights.
#
"""Routines for generating image plots."""
from __future__ import absolute_import

import colorsys
import locale
import os
import time
import logging

try:
    from PIL import Image, ImageDraw
except ImportError:
    import Image, ImageDraw

from six.moves import zip
import six

import weeplot.utilities
from weeplot.utilities import tobgr
import weeutil.weeutil
import weewx

log = logging.getLogger(__name__)

class GeneralPlot(object):
    """Holds various parameters necessary for a plot. It should be specialized by the type of plot.
    """
    def __init__(self, config_dict):
        """Initialize an instance of GeneralPlot.
        
        config_dict: an instance of ConfigObj, or something that looks like it.
        """

        self.line_list = []
        
        self.xscale = (None, None, None)
        self.yscale = (None, None, None)

        self.anti_alias             = int(config_dict.get('anti_alias',  1))

        self.image_width            = int(config_dict.get('image_width',  300)) * self.anti_alias
        self.image_height           = int(config_dict.get('image_height', 180)) * self.anti_alias
        self.image_background_color = tobgr(config_dict.get('image_background_color', '0xf5f5f5'))

        self.chart_background_color = tobgr(config_dict.get('chart_background_color', '0xd8d8d8'))
        self.chart_gridline_color   = tobgr(config_dict.get('chart_gridline_color',   '0xa0a0a0'))
        color_list                  = config_dict.get('chart_line_colors', ['0xff0000', '0x00ff00', '0x0000ff'])
        fill_color_list             = config_dict.get('chart_fill_colors', color_list)
        width_list                  = config_dict.get('chart_line_width',  [1, 1, 1])
        self.chart_line_colors      = [tobgr(v) for v in color_list]
        self.chart_fill_colors      = [tobgr(v) for v in fill_color_list]
        self.chart_line_widths      = [int(v) for v in width_list]

        
        self.top_label_font_path    = config_dict.get('top_label_font_path')
        self.top_label_font_size    = int(config_dict.get('top_label_font_size', 10)) * self.anti_alias

        self.unit_label             = None
        self.unit_label_font_path   = config_dict.get('unit_label_font_path')
        self.unit_label_font_color  = tobgr(config_dict.get('unit_label_font_color', '0x000000'))
        self.unit_label_font_size   = int(config_dict.get('unit_label_font_size', 10)) * self.anti_alias
        self.unit_label_position    = (10 * self.anti_alias, 0)

        self.bottom_label           = u""
        self.bottom_label_font_path = config_dict.get('bottom_label_font_path')
        self.bottom_label_font_color= tobgr(config_dict.get('bottom_label_font_color', '0x000000'))
        self.bottom_label_font_size = int(config_dict.get('bottom_label_font_size', 10)) * self.anti_alias
        self.bottom_label_offset    = int(config_dict.get('bottom_label_offset', 3))

        self.axis_label_font_path   = config_dict.get('axis_label_font_path')
        self.axis_label_font_color  = tobgr(config_dict.get('axis_label_font_color', '0x000000'))
        self.axis_label_font_size   = int(config_dict.get('axis_label_font_size', 10)) * self.anti_alias

        self.x_label_format         = config_dict.get('x_label_format')
        self.y_label_format         = config_dict.get('y_label_format')
        
        self.x_nticks               = int(config_dict.get('x_nticks', 10))
        self.y_nticks               = int(config_dict.get('y_nticks', 10))

        self.x_label_spacing        = int(config_dict.get('x_label_spacing', 2))
        self.y_label_spacing        = int(config_dict.get('y_label_spacing', 2))
        
        # Calculate sensible margins for the given image and font sizes.
        self.y_label_side = config_dict.get('y_label_side','left')
        if self.y_label_side == 'left' or self.y_label_side == 'both':
            self.lmargin = int(4.0 * self.axis_label_font_size)
        else:
            self.lmargin = 20 * self.anti_alias
        if self.y_label_side == 'right' or self.y_label_side == 'both':
            self.rmargin = int(4.0 * self.axis_label_font_size)
        else:
            self.rmargin = 20 * self.anti_alias
        self.bmargin = int(1.5 * (self.bottom_label_font_size + self.axis_label_font_size) + 0.5)
        self.tmargin = int(1.5 * self.top_label_font_size + 0.5)
        self.tbandht = int(1.2 * self.top_label_font_size + 0.5)
        self.padding =  3 * self.anti_alias

        self.render_rose            = False
        self.rose_width             = int(config_dict.get('rose_width', 21))
        self.rose_height            = int(config_dict.get('rose_height', 21))
        self.rose_diameter          = int(config_dict.get('rose_diameter', 10))
        self.rose_position          = (self.lmargin + self.padding + 5, self.image_height - self.bmargin - self.padding - self.rose_height)
        self.rose_rotation          = None
        self.rose_label             = config_dict.get('rose_label', u'N')
        self.rose_label_font_path   = config_dict.get('rose_label_font_path', self.bottom_label_font_path)
        self.rose_label_font_size   = int(config_dict.get('rose_label_font_size', 10))  
        self.rose_label_font_color  = tobgr(config_dict.get('rose_label_font_color', '0x000000'))
        self.rose_line_width        = int(config_dict.get('rose_line_width', 1))
        self.rose_color             = config_dict.get('rose_color')
        if self.rose_color is not None:
            self.rose_color = tobgr(self.rose_color)

        # Show day/night transitions
        self.show_daynight          = weeutil.weeutil.tobool(config_dict.get('show_daynight', False))
        self.daynight_day_color     = tobgr(config_dict.get('daynight_day_color', '0xffffff'))
        self.daynight_night_color   = tobgr(config_dict.get('daynight_night_color', '0xf0f0f0'))
        self.daynight_edge_color    = tobgr(config_dict.get('daynight_edge_color', '0xefefef'))
        self.daynight_gradient      = int(config_dict.get('daynight_gradient', 20))

        # initialize the location
        self.latitude               = None
        self.longitude              = None

        # normalize the font paths relative to the skin directory
        skin_dir = config_dict.get('skin_dir', '')
        self.top_label_font_path = self.normalize_path(skin_dir, self.top_label_font_path)
        self.bottom_label_font_path = self.normalize_path(skin_dir, self.bottom_label_font_path)
        self.unit_label_font_path = self.normalize_path(skin_dir, self.unit_label_font_path)
        self.axis_label_font_path = self.normalize_path(skin_dir, self.axis_label_font_path)
        self.rose_label_font_path = self.normalize_path(skin_dir, self.rose_label_font_path)

    @staticmethod
    def normalize_path(skin_dir, path):
        if path is None:
            return None
        return os.path.join(skin_dir, path)

    def setBottomLabel(self, bottom_label):
        """Set the label to be put at the bottom of the plot. """
        self.bottom_label = bottom_label
        
    def setUnitLabel(self, unit_label):
        """Set the label to be used to show the units of the plot. """
        self.unit_label = unit_label
        
    def setXScaling(self, xscale):
        """Set the X scaling.
        
        xscale: A 3-way tuple (xmin, xmax, xinc)
        """
        self.xscale = xscale
        
    def setYScaling(self, yscale):
        """Set the Y scaling.
        
        yscale: A 3-way tuple (ymin, ymax, yinc)
        """
        self.yscale = yscale
        
    def addLine(self, line):
        """Add a line to be plotted.
        
        line: an instance of PlotLine
        """
        if None in line.x:
            raise weeplot.ViolatedPrecondition("X vector cannot have any values 'None' ")
        self.line_list.append(line)

    def setLocation(self, lat, lon):
        self.latitude  = lat
        self.longitude = lon
        
    def setDayNight(self, showdaynight, daycolor, nightcolor, edgecolor):
        """Configure day/night bands.

        showdaynight: Boolean flag indicating whether to draw day/night bands

        daycolor: color for day bands

        nightcolor: color for night bands

        edgecolor: color for transition between day and night
        """
        self.show_daynight = showdaynight
        self.daynight_day_color = daycolor
        self.daynight_night_color = nightcolor
        self.daynight_edge_color = edgecolor

    def render(self):
        """Traverses the universe of things that have to be plotted in this image, rendering
        them and returning the results as a new Image object.
        """

        # NB: In what follows the variable 'draw' is an instance of an ImageDraw object and is in pixel units.
        # The variable 'sdraw' is an instance of ScaledDraw and its units are in the "scaled" units of the plot
        # (e.g., the horizontal scaling might be for seconds, the vertical for degrees Fahrenheit.)
        image = Image.new("RGB", (self.image_width, self.image_height), self.image_background_color)
        draw = self._getImageDraw(image)
        draw.rectangle(((self.lmargin,self.tmargin), 
                        (self.image_width - self.rmargin, self.image_height - self.bmargin)), 
                        fill=self.chart_background_color)
        
        self._renderBottom(draw)
        self._renderTopBand(draw)
        
        self._calcXScaling()
        self._calcYScaling()
        self._calcXLabelFormat()
        self._calcYLabelFormat()
        
        sdraw = self._getScaledDraw(draw)
        if self.show_daynight:
            self._renderDayNight(sdraw)
        self._renderXAxes(sdraw)
        self._renderYAxes(sdraw)
        self._renderPlotLines(sdraw)
        if self.render_rose:
            self._renderRose(image, draw)

        if self.anti_alias != 1:
            image.thumbnail((self.image_width / self.anti_alias, self.image_height / self.anti_alias), Image.ANTIALIAS)

        return image

    # noinspection PyMethodMayBeStatic
    def _getImageDraw(self, image):
        """Returns an instance of ImageDraw with the proper dimensions and background color"""
        draw = UniDraw(image)
        return draw
    
    def _getScaledDraw(self, draw):
        """Returns an instance of ScaledDraw, with the appropriate scaling.
        
        draw: An instance of ImageDraw
        """
        sdraw = weeplot.utilities.ScaledDraw(draw, ((self.lmargin + self.padding, self.tmargin + self.padding),
                                                    (self.image_width - self.rmargin - self.padding, self.image_height - self.bmargin - self.padding)),
                                                    ((self.xscale[0], self.yscale[0]), (self.xscale[1], self.yscale[1])))
        return sdraw
        
    def _renderDayNight(self, sdraw):
        """Draw vertical bands for day/night."""
        (first, transitions) = weeutil.weeutil.getDayNightTransitions(
            self.xscale[0], self.xscale[1], self.latitude, self.longitude)
        color = self.daynight_day_color \
            if first == 'day' else self.daynight_night_color
        xleft = self.xscale[0]
        for x in transitions:
            sdraw.rectangle(((xleft,self.yscale[0]),
                             (x,self.yscale[1])), fill=color)
            xleft = x
            color = self.daynight_night_color \
                if color == self.daynight_day_color else self.daynight_day_color
        sdraw.rectangle(((xleft,self.yscale[0]),
                         (self.xscale[1],self.yscale[1])), fill=color)
        if self.daynight_gradient:
            if first == 'day':
                color1 = self.daynight_day_color
                color2 = self.daynight_night_color
            else:
                color1 = self.daynight_night_color
                color2 = self.daynight_day_color
            nfade = self.daynight_gradient
            # gradient is longer at the poles than the equator
            d = 120 + 300 * (1 - (90.0 - abs(self.latitude)) / 90.0)
            for i in range(len(transitions)):
                last_ = self.xscale[0] if i == 0 else transitions[i-1]
                next_ = transitions[i+1] if i < len(transitions)-1 else self.xscale[1]
                for z in range(1,nfade):
                    c = blend_hls(color2, color1, float(z)/float(nfade))
                    rgbc = int2rgbstr(c)
                    x1 = transitions[i]-d*(nfade+1)/2+d*z
                    if last_ < x1 < next_:
                        sdraw.rectangle(((x1, self.yscale[0]),
                                         (x1+d, self.yscale[1])),
                                        fill=rgbc)
                if color1 == self.daynight_day_color:
                    color1 = self.daynight_night_color
                    color2 = self.daynight_day_color
                else:
                    color1 = self.daynight_day_color
                    color2 = self.daynight_night_color
        # draw a line at the actual sunrise/sunset
        for x in transitions:
            sdraw.line((x,x),(self.yscale[0],self.yscale[1]),
                       fill=self.daynight_edge_color)

    def _renderXAxes(self, sdraw):
        """Draws the x axis and vertical constant-x lines, as well as the labels. """

        axis_label_font = weeplot.utilities.get_font_handle(self.axis_label_font_path,
                                                            self.axis_label_font_size)

        drawlabelcount = 0
        for x in weeutil.weeutil.stampgen(self.xscale[0], self.xscale[1], self.xscale[2]) :
            sdraw.line((x, x), (self.yscale[0], self.yscale[1]), fill=self.chart_gridline_color,
                       width=self.anti_alias)
            if drawlabelcount % self.x_label_spacing == 0 :
                xlabel = self._genXLabel(x)
                axis_label_size = sdraw.draw.textsize(xlabel, font=axis_label_font)
                xpos = sdraw.xtranslate(x)
                sdraw.draw.text((xpos - axis_label_size[0]/2, self.image_height - self.bmargin + 2),
                                xlabel, fill=self.axis_label_font_color, font=axis_label_font)
            drawlabelcount += 1

    def _renderYAxes(self, sdraw):
        """Draws the y axis and horizontal constant-y lines, as well as the labels.
        Should be sufficient for most purposes.
        """
        nygridlines     = int((self.yscale[1] - self.yscale[0]) / self.yscale[2] + 1.5)
        axis_label_font = weeplot.utilities.get_font_handle(self.axis_label_font_path,
                                                                self.axis_label_font_size)
        
        # Draw the (constant y) grid lines 
        for i in range(nygridlines) :
            y = self.yscale[0] + i * self.yscale[2]
            sdraw.line((self.xscale[0], self.xscale[1]), (y, y), fill=self.chart_gridline_color,
                       width=self.anti_alias)
            # Draw a label on every other line:
            if i % self.y_label_spacing == 0 :
                ylabel = self._genYLabel(y)
                axis_label_size = sdraw.draw.textsize(ylabel, font=axis_label_font)
                ypos = sdraw.ytranslate(y)
                if self.y_label_side == 'left' or self.y_label_side == 'both':
                    sdraw.draw.text( (self.lmargin - axis_label_size[0] - 2, ypos - axis_label_size[1]/2),
                                ylabel, fill=self.axis_label_font_color, font=axis_label_font)
                if self.y_label_side == 'right' or self.y_label_side == 'both':
                    sdraw.draw.text( (self.image_width - self.rmargin + 4, ypos - axis_label_size[1]/2),
                                ylabel, fill=self.axis_label_font_color, font=axis_label_font)

    def _renderPlotLines(self, sdraw):
        """Draw the collection of lines, using a different color for each one. Because there is
        a limited set of colors, they need to be recycled if there are very many lines.
        """
        nlines = len(self.line_list)
        ncolors = len(self.chart_line_colors)
        nfcolors = len(self.chart_fill_colors)
        nwidths = len(self.chart_line_widths)

        # Draw them in reverse order, so the first line comes out on top of the image
        for j, this_line in enumerate(self.line_list[::-1]):
            
            iline=nlines-j-1
            color = self.chart_line_colors[iline%ncolors] if this_line.color is None else this_line.color
            fill_color = self.chart_fill_colors[iline%nfcolors] if this_line.fill_color is None else this_line.fill_color
            width = (self.chart_line_widths[iline%nwidths] if this_line.width is None else this_line.width) * self.anti_alias

            # Calculate the size of a gap in data
            maxdx = None
            if this_line.gap_fraction is not None:
                maxdx = this_line.gap_fraction * (self.xscale[1] - self.xscale[0])

            if this_line.plot_type == 'line' :
                ms = this_line.marker_size
                if ms is not None:
                    ms *= self.anti_alias
                sdraw.line(this_line.x, 
                           this_line.y, 
                           line_type=this_line.line_type,
                           marker_type=this_line.marker_type,
                           marker_size=ms,
                           fill  = color,
                           width = width,
                           maxdx = maxdx)
            elif this_line.plot_type == 'bar' :
                for x, y, bar_width in zip(this_line.x, this_line.y, this_line.bar_width):
                    if y is None:
                        continue
                    sdraw.rectangle(((x - bar_width, self.yscale[0]), (x, y)), fill=fill_color, outline=color)
            elif this_line.plot_type == 'vector' :
                for (x, vec) in zip(this_line.x, this_line.y):
                    sdraw.vector(x, vec,
                                 vector_rotate = this_line.vector_rotate,
                                 fill  = color,
                                 width = width)
                self.render_rose = True
                self.rose_rotation = this_line.vector_rotate
                if self.rose_color is None:
                    self.rose_color = color

    def _renderBottom(self, draw):
        """Draw anything at the bottom (just some text right now). """
        bottom_label_font = weeplot.utilities.get_font_handle(self.bottom_label_font_path, self.bottom_label_font_size)
        bottom_label_size = draw.textsize(self.bottom_label, font=bottom_label_font)
        
        draw.text(((self.image_width - bottom_label_size[0])/2, 
                   self.image_height - bottom_label_size[1] - self.bottom_label_offset),
                  self.bottom_label, 
                  fill=self.bottom_label_font_color,
                  font=bottom_label_font)
        
    def _renderTopBand(self, draw):
        """Draw the top band and any text in it. """
        # Draw the top band rectangle
        draw.rectangle(((0,0), 
                        (self.image_width, self.tbandht)), 
                        fill = self.chart_background_color)

        # Put the units in the upper left corner
        unit_label_font = weeplot.utilities.get_font_handle(self.unit_label_font_path, self.unit_label_font_size)
        if self.unit_label:
            if self.y_label_side == 'left' or self.y_label_side == 'both':
                draw.text(self.unit_label_position,
                          self.unit_label,
                          fill=self.unit_label_font_color,
                          font=unit_label_font)
            if self.y_label_side == 'right' or self.y_label_side == 'both':
                unit_label_position_right = (self.image_width - self.rmargin + 4, 0)
                draw.text(unit_label_position_right,
                          self.unit_label,
                          fill=self.unit_label_font_color,
                          font=unit_label_font)

        top_label_font = weeplot.utilities.get_font_handle(self.top_label_font_path, self.top_label_font_size)
        
        # The top label is the appended label_list. However, it has to be drawn in segments 
        # because each label may be in a different color. For now, append them together to get
        # the total width
        top_label = ' '.join([line.label for line in self.line_list])
        top_label_size = draw.textsize(top_label, font=top_label_font)
        
        x = (self.image_width - top_label_size[0])/2
        y = 0
        
        ncolors = len(self.chart_line_colors)
        for i, this_line in enumerate(self.line_list):
            color = self.chart_line_colors[i%ncolors] if this_line.color is None else this_line.color
            # Draw a label
            draw.text( (x,y), this_line.label, fill = color, font = top_label_font)
            # Now advance the width of the label we just drew, plus a space:
            label_size = draw.textsize(this_line.label + ' ', font= top_label_font)
            x += label_size[0]

    def _renderRose(self, image, draw):
        """Draw a compass rose."""
        
        rose_center_x = self.rose_width/2  + 1
        rose_center_y = self.rose_height/2 + 1
        barb_width  = 3
        barb_height = 3
        # The background is all white with a zero alpha (totally transparent)
        rose_image = Image.new("RGBA", (self.rose_width, self.rose_height), (0x00, 0x00, 0x00, 0x00))
        rose_draw = ImageDraw.Draw(rose_image)
 
        fill_color = add_alpha(self.rose_color)
        # Draw the arrow straight up (North). First the shaft:
        rose_draw.line( ((rose_center_x, 0), (rose_center_x, self.rose_height)), width = self.rose_line_width, fill = fill_color)
        # Now the left barb:
        rose_draw.line( ((rose_center_x - barb_width, barb_height), (rose_center_x, 0)), width = self.rose_line_width, fill = fill_color)
        # And the right barb:
        rose_draw.line( ((rose_center_x, 0), (rose_center_x + barb_width, barb_height)), width = self.rose_line_width, fill = fill_color)
        
        rose_draw.ellipse(((rose_center_x - self.rose_diameter/2,
                            rose_center_y - self.rose_diameter/2),
                           (rose_center_x + self.rose_diameter/2,
                            rose_center_y + self.rose_diameter/2)),
                          outline = fill_color)

        # Rotate if necessary:
        if self.rose_rotation:
            rose_image = rose_image.rotate(self.rose_rotation)
            rose_draw = ImageDraw.Draw(rose_image)
        
        # Calculate the position of the "N" label:
        rose_label_font = weeplot.utilities.get_font_handle(self.rose_label_font_path, self.rose_label_font_size)
        rose_label_size = draw.textsize(self.rose_label, font=rose_label_font)
        
        # Draw the label in the middle of the (possibly) rotated arrow
        rose_draw.text((rose_center_x - rose_label_size[0]/2 - 1,
                        rose_center_y - rose_label_size[1]/2 - 1),
                        self.rose_label,
                        fill = add_alpha(self.rose_label_font_color),
                        font = rose_label_font)

        # Paste the image of the arrow on to the main plot. The alpha
        # channel of the image will be used as the mask.
        # This will cause the arrow to overlay the background plot
        image.paste(rose_image, self.rose_position, rose_image)
        

    def _calcXScaling(self):
        """Calculates the x scaling. It will probably be specialized by
        plots where the x-axis represents time.
        """
        (xmin, xmax) = self._calcXMinMax()

        self.xscale = weeplot.utilities.scale(xmin, xmax, self.xscale, nsteps=self.x_nticks)
            
    def _calcYScaling(self):
        """Calculates y scaling. Can be used 'as-is' for most purposes."""
        # The filter is necessary because unfortunately the value 'None' is not
        # excluded from min and max (i.e., min(None, x) is not necessarily x). 
        # The try block is necessary because min of an empty list throws a
        # ValueError exception.
        ymin = ymax = None
        for line in self.line_list:
            if line.plot_type == 'vector':
                try:
                    # For progressive vector plots, we want the magnitude of the complex vector
                    yline_max = max(abs(c) for c in [v for v in line.y if v is not None])
                except ValueError:
                    yline_max = None
                yline_min = - yline_max if yline_max is not None else None
            else:
                yline_min = weeutil.weeutil.min_with_none(line.y)
                yline_max = weeutil.weeutil.max_with_none(line.y)
            ymin = weeutil.weeutil.min_with_none([ymin, yline_min])
            ymax = weeutil.weeutil.max_with_none([ymax, yline_max])

        if ymin is None and ymax is None :
            # No valid data. Pick an arbitrary scaling
            self.yscale=(0.0, 1.0, 0.2)
        else:
            try:
                self.yscale = weeplot.utilities.scale(ymin, ymax, self.yscale, nsteps=self.y_nticks)
            except ValueError as e:
                log.error("scale error %s" % e)
                log.error("ymin=%s; ymax=%s; yscale=%s, y_nticks=%s"
                          % (ymin, ymax, self.yscale, self.y_nticks))
                raise

    def _calcXLabelFormat(self):
        if self.x_label_format is None:
            self.x_label_format = weeplot.utilities.pickLabelFormat(self.xscale[2])

    def _calcYLabelFormat(self):
        if self.y_label_format is None:
            self.y_label_format = weeplot.utilities.pickLabelFormat(self.yscale[2])
        
    def _genXLabel(self, x):
        xlabel = locale.format_string(self.x_label_format, x)
        return xlabel
    
    def _genYLabel(self, y):
        ylabel = locale.format_string(self.y_label_format, y)
        return ylabel
    
    def _calcXMinMax(self):
        xmin = xmax = None
        for line in self.line_list:
            xline_min = weeutil.weeutil.min_with_none(line.x)
            xline_max = weeutil.weeutil.max_with_none(line.x)
            # If the line represents a bar chart, then the actual minimum has to
            # be adjusted for the bar width of the first point
            if line.plot_type == 'bar':
                xline_min = xline_min - line.bar_width[0]
            xmin = weeutil.weeutil.min_with_none([xmin, xline_min])
            xmax = weeutil.weeutil.max_with_none([xmax, xline_max])
        return (xmin, xmax)

class TimePlot(GeneralPlot) :
    """Class that specializes GeneralPlot for plots where the x-axis is time."""
    
    def _calcXScaling(self):
        """Specialized version for time plots."""
        if None in self.xscale:
            (xmin, xmax) = self._calcXMinMax()
            self.xscale = weeplot.utilities.scaletime(xmin, xmax)

    def _calcXLabelFormat(self):
        """Specialized version for time plots."""
        if self.x_label_format is None:
            (xmin, xmax) = self._calcXMinMax()
            if xmin is not None and xmax is not None:
                delta = xmax - xmin
                if delta > 30*24*3600:
                    self.x_label_format = u"%x"
                elif delta > 24*3600:
                    self.x_label_format = u"%x %X"
                else:
                    self.x_label_format = u"%X"
        
    def _genXLabel(self, x):
        if self.x_label_format is None:
            return ''
        time_tuple = time.localtime(x)
        # There are still some strftimes out there that don't support Unicode.
        try:
            xlabel = time.strftime(self.x_label_format, time_tuple)
        except UnicodeEncodeError:
            # Convert it to UTF8, then back again:
            xlabel = time.strftime(self.x_label_format.encode('utf-8'), time_tuple).decode('utf-8')
        return xlabel


class PlotLine(object):
    """Represents a single line (or bar) in a plot. """
    def __init__(self, x, y, label='', color=None, fill_color=None, width=None, plot_type='line',
                 line_type='solid', marker_type=None, marker_size=10, 
                 bar_width=None, vector_rotate = None, gap_fraction=None):
        self.x               = x
        self.y               = y
        self.label           = label
        self.plot_type       = plot_type
        self.line_type       = line_type
        self.marker_type     = marker_type
        self.marker_size     = marker_size
        self.color           = color
        self.fill_color      = fill_color
        self.width           = width
        self.bar_width       = bar_width
        self.vector_rotate   = vector_rotate
        self.gap_fraction    = gap_fraction

class UniDraw(ImageDraw.ImageDraw):
    """Supports non-Unicode fonts
    
    Not all fonts support Unicode characters. These will raise a UnicodeEncodeError exception.
    This class subclasses the regular ImageDraw.Draw class, adding overridden functions to
    catch these exceptions. It then tries drawing the string again, this time as a UTF8 string
    """
    
    def text(self, position, string, **options):
        try:
            return ImageDraw.ImageDraw.text(self, position, string, **options)
        except UnicodeEncodeError:
            return ImageDraw.ImageDraw.text(self, position, string.encode('utf-8'), **options)
        
    def textsize(self, string, **options):
        try:
            return ImageDraw.ImageDraw.textsize(self, string, **options)
        except UnicodeEncodeError:
            return ImageDraw.ImageDraw.textsize(self, string.encode('utf-8'), **options)
            
            
def blend_hls(c, bg, alpha):
    """Fade from c to bg using alpha channel where 1 is solid and 0 is
    transparent.  This fades across the hue, saturation, and lightness."""
    return blend(c, bg, alpha, alpha, alpha)

def blend_ls(c, bg, alpha):
    """Fade from c to bg where 1 is solid and 0 is transparent.
    Change only the lightness and saturation, not hue."""
    return blend(c, bg, 1.0, alpha, alpha)

def blend(c, bg, alpha_h, alpha_l, alpha_s):
    """Fade from c to bg in the hue, lightness, saturation colorspace.
       Added hue directionality to choose shortest circular hue path e.g.
       https://stackoverflow.com/questions/1416560/hsl-interpolation
       Also, grey detection to minimize colour wheel travel.  Interesting resource:
       http://davidjohnstone.net/pages/lch-lab-colour-gradient-picker
       """

    r1,g1,b1 = int2rgb(c)
    h1,l1,s1 = colorsys.rgb_to_hls(r1/255.0, g1/255.0, b1/255.0)

    r2,g2,b2 = int2rgb(bg)
    h2,l2,s2 = colorsys.rgb_to_hls(r2/255.0, g2/255.0, b2/255.0)

    # Check if either of the values is grey (saturation 0),
    # in which case don't needlessly reset hue to '0', reducing travel around colour wheel
    if s1 == 0: h1 = h2
    if s2 == 0: h2 = h1

    h_delta = h2 - h1

    if abs(h_delta) > 0.5:
        # If interpolating over more than half-circle (0.5 radians) take shorter, opposite direction...
        h_range = 1.0 - abs(h_delta)
        h_dir = +1.0 if h_delta < 0.0 else -1.0

        # Calculte h based on line back from h2 as proportion of h_range and alpha
        h = h2 - ( h_dir * h_range * alpha_h )

        # Clamp h within 0.0 to 1.0 range
        h = h + 1.0 if h < 0.0 else h
        h = h - 1.0 if h > 1.0 else h
    else:
        # Interpolating over less than a half-circle, so use normal interpolation as before
        h = alpha_h * h1 + (1 - alpha_h) * h2

    l = alpha_l * l1 + (1 - alpha_l) * l2
    s = alpha_s * s1 + (1 - alpha_s) * s2

    r,g,b = colorsys.hls_to_rgb(h, l, s)

    r = round(r * 255.0)
    g = round(g * 255.0)
    b = round(b * 255.0)

    t = rgb2int(int(r),int(g),int(b))

    return int(t)

def int2rgb(x):
    b = (x >> 16) & 0xff
    g = (x >> 8) & 0xff
    r = x & 0xff
    return r,g,b

def int2rgbstr(x):
    return '#%02x%02x%02x' % int2rgb(x)

def rgb2int(r,g,b):
    return r + g*256 + b*256*256

def add_alpha(i):
    """Add an opaque alpha channel to an integer RGB value"""
    r = i & 0xff
    g = (i >> 8)  & 0xff
    b = (i >> 16) & 0xff
    a = 0xff    # Opaque alpha
    return r,g,b,a

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