by Timothy D. Witham

Years ago I wrote unix weather station software named wx200d. It was named after the WX200 weather station sold by Radio Shack, but now it supports other weather stations as well. These hardware devices collect the usual weather variables and report it to the computer through a serial port. wx200d then stores the data in files and makes it available to remote clients. Back then, I used perl and gnuplot to make some rudimentary graphs.

Then I discovered RRDtool and realized the power to make much better looking and more useful charts. When thinking of how to present my data, I wanted to see min, max and average for each primary variable. And I wanted to see either all variables for one time period, or one variable for different time periods. So what I really wanted was a "matrix" of variables and times where you could look at any "row" or "column" of the matrix as one web page of several charts.

To implement this, I wrote a perl script that defines the rrdgraph code that applies to all graphs, to each variable and to each time frame. It then loops over the times and variables and generates the HTML pages. These are piped through rrdcgi --filter to create the graphs. This way the matrix of related graphs are created consistently without any redundant code.

Click the images to get to that graph in my current weather matrix. Then click the graph again to toggle the time / variable view.