While processing some data at work today I had an issue where I had a raster dataset in ArcGIS, where all cells with invalid data had been set to 9999. Of course, this caused a lot of issues for the statistics on the dataset – basically they were all nonsense – so I needed to […]
In my field I often need to plot polar contour plots, and generally plotting tools don’t make this easy. In fact, I think I could rate every single graphing/plotting package in the world by the ease of producing a polar contour plot – and most would fail entirely! Still, I have managed to find a […]
UPDATE: I’ve created a new site to host my John Snow data, and included various other modern formats (GeoPackage, GeoJSON etc). Please go there to download the data. In 1854 there was a massive cholera outbreak in Soho, London – in three days over 120 people died from the disease. Famously, John Snow plotted the […]
When you try and reproject a dataset in ArcGIS (for example, by using the Project Raster tool) you will see a dialog a bit like the one below: The highlighted field wants you to specific a Geographic Tranformation. Although it says that it is optional, it often isn’t (I think the optionality depends on the type […]
I often find myself using Julian days as a simple method to represent dates in my code. It’s nice and easy, because every day is simply an integer (the number of days since the beginning of the year) and any time during the day can be represented as a floating point number (the fraction of […]
If you are creating maps then for goodness sake Use sensible colours! I was helping some undergraduates with some work the other day, and they decided to use the following colour scheme for representing river depth: Deep water: Red Medium-depth water: Bright green Shallow water: Pink Why did they do this? Well, either they were […]
I’m starting a new series here on my blog about interesting and somewhat out-of-the-ordinary applications of remote sensing. So…here is number 1. An analysis firm called Remote Sensing Metrics LLC has been using satellite images to predict changes in the profits of firms such as Walmart, and thus help predict share prices. How does this […]
When doing a course in Computer Vision last year I was introduced to the Lena image: This was originally a scan from Playboy magazine in 1972, but has taken on a life of its own as a test image in the field computer vision. The (very interesting) history of it is described on the Wikipedia page and […]
Many fields have a collection of rules of thumb – tacit knowledge that isn’t often talked about, but is often used in the field. Some of these rules have come from published information (papers, books, presentations etc) and some has just grown up over the years. This post isn’t anywhere near done yet – I’m going […]
As part of the OS Open Data initiative the Ordnance Survey has released a free version of their 1:50,000 scale gazetteer. This lists all of the names shown on the 1:50,000 scale OS maps, linked to information such as their location (in both Ordnance Survey grid references and WGS84 latitude/longitude pairs) and type (city, town, water […]