weewx-svg2png

Convert SVG to PNG during skin creation

mini weather card	thumbnail	webcam image	forecast

Using this generator you can

• create thumbnail images for the web pages created by WeeWX
• create weather cards
• put actual weather data onto webcam images

It is intended to create the SVG files by the CheetahGenerator functionality of WeeWX.

Prerequisites

First, install CairoSVG, if it is not already there.

sudo apt-get install cairosvg

This will install python3-cairosvg as well.

Installation instructions

1. download

   wget -O weewx-svg2png.zip https://github.com/roe-dl/weewx-svg2png/archive/master.zip
   

2. run the installer

   WeeWX up to version 4.X

   sudo wee_extension --install weewx-svg2png.zip
   

   WeeWX from version 5.0 on

   sudo weectl extension install weewx-svg2png.zip
   

3. edit configuration in skin.conf

   See section "Configuration instructions"

4. restart weewx

   for SysVinit systems:

   sudo /etc/init.d/weewx stop
   sudo /etc/init.d/weewx start
   

   for systemd systems:

   sudo systemctl stop weewx
   sudo systemctl start weewx
   

Configuration instructions

This is for use in skins. Add a reference to this generator to the generator_list key in skin.conf:

[Generators]
    generator_list = ..., user.svg2png.SVGtoPNGGenerator

Then, add a section to skin.conf to configure the files to be created as SVG and converted to PNG (replace index_thumbnail by your file name and file1 to something reasonable for you):

[CheetahGenerator]
    ...
    [[ToDate]]
        ...
        [[[file1]]]
            template = index_thumbnail.svg.tmpl
...
[SVGtoPNGGenerator]
    [[file1]]
        # file name without extension (optional)
        file = index_thumbnail
        # image width in pixels (optional)
        width = replace_me
        # image height in pixels (optional)
        height = replace_me
    ...

If width and height are not provided, they will be taken out of the SVG file header.

If the file key is missing, the section name is used instead.

Fonts

If you want to use special fonts within your SVG files you need to inform the system about the existence of those fonts. This is done by linking the font files or the directory containing the font files to /usr/local/share/fonts. After that you have to update the font cache.

Assuming your fonts reside in /etc/weewx/skins/Belchertown/lib/fonts/ you will enter:

cd /usr/local/share/fonts
sudo ln -s /etc/weewx/skins/Belchertown/lib/fonts belchertown-fonts
sudo fc-cache /usr/local/share/fonts

Please note, that this requires to download the fonts and store them locally.

Now you can reference your fonts within the <style> section of your SVG file template. Assuming your font is called Roboto (a font provided by Google and used within the Belchertown skin) you would write:

    text {
        font-family: Roboto, sans-serif;
    }

Usage

See the examples directory for example WeeWX templates to create an SVG file.

Examples

The examples include instructions how to

• have actual weather data on the created image
• include images from image files like webcam pictures or weather symbols
• create graphs of readings

Another example, this time involving DWD forecasts, you find in the weewx-DWD wiki.

Thumbnail or preview image for social media references

In social media posts that reference web pages you often see a preview image of the web page shown below the post. You may have wondered how this is done.

It is quite easy. You only need a thumbnail image as created by this generator and a special <meta> statement within the header section of your web page referencing it. Assuming your thumbnail is named index_thumbnail.png and your domain is example.com this reads like this:

        <meta name="twitter:image" content="https://www.example.com/index_thumbnail.png?v=$current.dateTime.raw" />
        <meta property="og:image" content="https://www.example.com/index_thumbnail.png?v=$current.dateTime.raw" />

You can also specify wether the thumbnail is shown as a small image besides the page description or as a large image above the page description.

• for small thumbnails

        <meta name="twitter:card" content="summary" />
  

• for large thumbnails

        <meta name="twitter:card" content="summary_large_image" />
  

Troubleshooting

• See the syslog for messages containing user.svg2png. They may reveal some reason for problems.

• To log the file names and paths set debug = 1 in weewx.conf and restart WeeWX

• If you see a log message like this

  Oct 12 15:21:08 XXXX weewx[12345] ERROR user.svg2png: URLError <urlopen error [Errno 2] Datei oder Verzeichnis nicht gefunden: '/var/www/html/somepath/somefile.jpg'>
  

  then there is a file reference within one of your templates that could not be resolved. Check the template and fix the path.

  Enter

  ls -l /var/www/html/somepath/somefile.jpg
  

  to see whether the file exists.

• Relative paths are not the same as absolute paths. So for example webcam/snap.jpg (without slash) is not the same as /webcam/snap.jpg (with slash). Make sure you know the real location of your files.

• Check file names carefully. For example snap.jpeg (including character e) is not the same as snap.jpg (without character e).

References

• WeeWX website
• WeeWX information in german
• WeeWX customization guide (See this guide for writing templates.)
• Calculation in templates
• Tags for series
• CairoSVG website
• The Belchertown skin