Saturday, December 16, 2017

New version of monthly webGL surface temperature map page.

Moyhu has a maintained page here showing monthly surface temperature anomalies in an interactive webGL spherical shaded plot. The anomalies are based on the TempLS analysis, using unadjusted GHCN V3 and ERSST V5. TempLS provides the triangular mesh and normals (base 1961-90), and the anomalies are just the station monthly averages with these subtracted. The shading is set to give correct color at the nodes (stations). It is updated daily, so also provides a detailed picture from early in the month (which means the first few days are sparse).

The page had used its own webGL program, with a month selection mechanism (using XMLHTTPrequest to dowload data). I have been developing a general webGL facility (described here), and I wanted to make a nw page that conforms with that. This makes extra facilities available and is easier for me to maintain.

To do this I had to extend the WebGL facility, to a version I am currently calling V2.2. It is a considerable restructure, which will probably become V3. It enables me to replace the constructors of various parts of the page within the user files that go with each application, rather than writing it into the core facility. There were issues with making variables (and functions) visible to functions defines in separate files. I'm also now rather extensively using the MoyJS library.

The functionality of older MoyGL versions is preserved, and so, I hope, is the functionality of the page. One novelty of the version is a reintroduction of the flat globe pointing mechanism, which I used before WebGL. In the top right corner is a world map; you can click on any place to make the globe turn to show this point in he centre, with the longitude vertical (oriented). Otherwise, it's pretty much as in V2.1 as used previously.

The month selector is different. It is the box in the top right corner:


The three colored bars let you select decade (1900-2010), year (0-9) and month(1-12). The black squares show the current selection. As you click on the bars, these move, and the date in the red box below changes accordingly. When you have the date you want, click "Fetch and Show" and the data will be retrieved and a new plot will appear.

Since I am using unadjusted anomalies (1961-90), some exceptions will show out. I discussed here a method for remedying this, and of course adjusted data would also help. I am not currently using that method, which makes extrapolated current expected value the anomaly base. It is good for recent years, but gets troublesome in earlier years. I may offer it as an alternative some time.


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