javascript

Accessing Cross Domain Data with YQL

The same origin policy prevents code from one domain accessing data from a different domain. For a mapping site requests for KML, GeoRSS, WFS services, and some WMS operations are all affected by this policy, and therefore require a range of workarounds, usually involving a proxy. One solution is the ExtJS ScriptTagProxy that can be […]



Will HTML5 Revolutionise Raster Web GIS?

Or perhaps that should be rephrased start browser-based raster GIS? GIS data is split into two base types – vector data – geometric shapes, usually further split into points, lines, and polygons, and raster data – cell-based or “pixelated” data. Graphics on the web mirror this divide. On the vector side SVG – scalable vector […]



Creating a Geodesic Circle in OpenLayers

I recently asked a question on GIS Stack Exchange on how to create a  buffer around a point that took into account the curvature of the earth. OpenLayers has support for geodesic measurements, but not creating geodesic polygons. Drawing a standard polygon on a Mercator projected map can produce features with very different measurements from […]



We Know Where Your Browser Lives

Maybe I’m a little late in finding this, but if you have FireFox 3.5 or higher try clicking this link (you will have to agree to let your browser divulge your location to open the link). The JavaScript code run when clicking the link is as follows, and can also be pasted directly into your […]



Watch out for OpenLayer Distances

I had the fortune on my most recent project, a MapFish mapping system, of having someone else do some thorough testing. One thing that had escaped me, was both the measure tool and area tool were returning incorrect results. The distance as-the-crow flies between Dublin and Cork is 219 kilometres (136.08 miles in old money) […]



Logging OpenLayers with Firebug

I take it as given that anyone developing with Firefox and OpenLayers has Firebug installed. Firebug has a number of powerful tools that can make the previous nightmare of JavaScript debugging tolerable. One feature I recently “discovered” are the logging options. It’s definitely a timesaver over my previous method of putting temporary alert(vals); throughout my […]



Minifying the Mapfish Client on Windows

This page has 72 external Javascript scripts. Try combining them into one. My YSlow Firefox plug-in was telling me that I had included too may JavaScript files, and that they should be combined into a single-file, and minified. The default setup of Mapfish has a single script include (mfbase\mapfish\MapFish.js), but this script  automatically loads around […]