Thursday, October 11, 2012

Fancy graphics and climate data

Over the last two years I've been exploring various ways of using interactivity to make climate data more accessible and attractive. I've been trying to maintain a gallery, but that takes time, and the effort has been lagging.

So I want to write a post which just summarizes the techniques used, to act mainly as a catalogue with pointers.

Here is a table of headings


KML, Google EarthSpaghetti graphs
Trend plotsEarth projections
HTML 5 and triangle meshesWebGL
Google MapsClimate Plotter

KML, Google Earth

The first thing I tried was writing Google Earth files, using their API language KML (of the XML family). This was really just to organise the data provided by the various surface temperature collectors (GHCN, GSOD, CRUTEM, BEST etc. I could show the stations with various colored and sized pins; summary information would appear in balloons on clicking. Then I found an even more useful capability with folders. GE lets you turn the folders on and off. So if I list stations in folders according to their decade of commencement, for example, the user can show a plot with and range of decades he wants.

The downside is that the user needs to download the KML files, or KMZ (a zipped equivalent). They are not excessively big. I have a collection here.

Anyway, the posts on this are here:


Fun with Google Earth, GSOD and KML

More Google Earth station data

Still more KML and Google Earth

GHCN KML visualisation by years

GE visualisation of changes to GHCN stations 1990...

A KMZ file for the BEST stations

A combined KMZ file for BEST, GHCN, GSOD and CRUTE...

Spaghetti graphs

I then looked at different ways of making "spaghetti" graphs (many tangled curves) more readable. I began with just color experiments, then fancy patterns, then a GIF animation (more here and here). But a suggestion from Eli, with advice from TheFordPrefect, got me using Javascript.

The user could, by hovering the mouse, select individual components of the plot in black contrast. Another such plot here included a general R program for generating code from a CSV data file. And this ice extent plot doesn't pick out curves but lets you focus on time ranges.

Trend plots

This series started with a ordinary graphic which showed, in a color triangle, how the total of possible trends from a single time series, over any time interval could be visualised. However, this was then adorned with JS facilities for choosing different datasets,. Then options were added so that the time series would be simultaneously plotted and the interval in question, and its trend, displayed. This would be updated by clicking on the colored triangle, or by controls on the time series graph. Numerical information, including later confidence limits, could be displayed. Here is a list:
A JS gadget for viewing temperature trends.
A picture of statistically significant warming.Observed SST and model trends
Significant trend differencesSignificant trends in Foster/Rahmstorf
Combined GMST trend viewer

Earth projections

I've never been happy with the various projections which attempt to render the whole earth on a page. I have preferred spherical projections, even though it requires several views. But JS creates a Google Earth like possibility - a spherical projection in which you can adjust the viewpoint.

Every month recently I have published a flat projection of a spherical harmonics fit to the temperatures anomalies, so this was a clear candidate. The globe views were typically from the corners of a surrounding cube. Examples are here:

A Javascript worldview for surface temp.April 2012 temperatures up 0.2°C

HTML 5 and triangle meshes

HTML 5 Canvases are relatively new. They offer huge flexibility for interactive graphing. This was developed in the climate plotter to be described, but the first application was to shading global plots. The canvas lets you prescribe colors at the corners of a triangle and it will then shade continuously between them, or at least between two of them. Getting all three right is harder to manage, unlike with Gouraud shading that does it automatically.

The big merit of this is that I can show temperature anomalies with no model fitting, so that colors will be correct at the stations. With the above caveat, it may be that only two thirds will be exactly right, but that's enough to see what is going on. When that is done, the mesh and stations can be shown, and the user can click to bring up station names and details. Again, a spherical projection is used, and can be user-rotated to an arbitrary view. I provide a navigator map (flat projection) on which you can click to choose the point to focus on. Examples are here:

Nov temps displayed with HTML 5Cherrypicker's guide to station trends
Visualizing 2011 temperature anomalies

WebGL

This new facility, described in a recent post, makes available the full power of GL, and is potentially an improvement on HTML5 with spherical triangle meshing. However, support from browsers is still patchy, and the JavaScript that implements it is more difficult to modify - GL has its own style that it is perilous to disrupt. Some day it will be the best option.

Google Maps

This is a different style of using Javascript. It creates the facilities of GE with KML, but in a browser window. Google makes its API available, and as in Maps style the globe can be traversed and flags shown of coded colors, with balloons of information in response to clicking etc. Control is by the familiar JS gadgets of radio buttons etc.

Google Maps display of GHCN stations, with Javas...

Climate Plotter

I think the most advanced use of Javascript and HTML 5 is with the Climate Plotter. This interactively draws plots from a store of annual climate data. You can form regressions (of just about anything with anything); you can plot against an image background. You can interactively rescale, show different axes with different units; adjust anomaly basis intervals. The history is here:


Interactive JS climate plotter (update)Interactive climate plotting news.
Interactive JS plotter Ver 2



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