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Getting Started guide for Sinatra with focus on development environment
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Lets create a simple application which displays the address entered by the user on the map within the application. We’ll call it MapApp.
Archive for March 2010
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Selection of points within specified radius of given lat/lon
I took a trip down to London yesterday to go to Rewired Culture, part of the series of Rewired State events. Basically these are gatherings of assorted hackers and geeks who get provided with access to government data, beer and pizza and left to see what they come up with.
The premise is that most government bodies don’t know what to do with their data, either because they don’t have the technical expertise or because they don’t care, or because they don’t see doing interesting things with their data as being part of their remit. Hackers by their very nature DO know what to do with it, so by letting them loose with the data means that interesting things tend to happen.
Rewired Culture was about data originating from the culture, media and sport sectors and took place at the Guardian. There were about 25 hackers – ranging in age from 15 to me – who took over an office in the Grauniad building (sorry about adjusting your chair, whoever’s desk it was I sat at) and spent the day coding. From what I could see it was a pretty mixed bunch – although Macs were in the ascendence, there was a web focus to it, and the tools were generally open source.
There were various outcomes of the day – my favourite being Rupert Redington‘s Awesometer. This is an antidote to the Asborometer, which to me sums up everything that’s wrong and negative about the reuse of goverment data. The Asborometer focusses on everything that’s negative – how many ASBOs are there in your area, and exactly how afraid should you be? Needless to say, it was inevitably picked up and praised by Gordon Brown as he “launched” the government’s latest “put-it-all-online” efforts last week.
The Awesometer is completely different. It picks up your location, scrapes a whole series of data sources to see what positive things are going in your area, gives you a score which includes +1 for *you* being there, and then tells you to relax and get on with things.
If it could further ram home the point that violent crime is very rare – and its prevalence is something that’s continually hyped-up by those with a vested interest in accentuating negativity for the furtherance of their own agendas – it would be perfect.
The whole event was only for the day, which isn’t a great deal of time to actually *make* something by my standards. However I did manage to come up with something that works as a cobbled-together prototype, more about which is over here.
English Heritage is a non-Departmental Public Body that exists to protect and promote England’s historic environment. One of the tools at their disposal is listing, which applies protection to a building or site through the planning system. Crudely, it stops you putting plastic double glazing into your historic thatched cottage; or demolishing a factory designed by that world-famous architect.
There are a lot of listed buildings – about 374,081 of them – and they’re listed in a database which English Heritage made available to the Rewired Culture event. It appears to have been a dump of some kind of GIS system – it’s in a dBase format and has eastings, northings and polygons for the structures. There’s no information about the buildings other than a name and a very truncated street address (there’s no town data, for example), but you can at least identify them geographically.
Job #1 is converting the eastings and northings to latitude and longitude. That’s painful maths, but a one-off process and thankfully doable through some PHP functions which someone else previously written. So a quick PHP script runs the conversion on the fly to convert from the supplied lat/long to the eastings/northings needed to interrogate the database.
Job #2 is being able to find out where the listed buildings around you are. This is another web service with a PHP backend that accepts a pair of lat/lon coordinates and a radius, and spits back a list of lat/lon coordinates of the buildings within the radius together with their names and street address.
I managed to get that pair of services more-or-less working during the day after a fair amount of tweaking, which just left the front-end piece – you can access the webservice at listedbuildings.adoptioncurve.net – it should be fairly self-explanatory.
Job #3 was entirely due to needing something to do on the 2-hour train ride back to Sheffield. This is a simple iPhone client which pick up your location from GPS and pings the aforementioned web service to grab a list of buildings in the locale. It then plots them as pins on the map to show what’s around you.
Because the resolution of the grid reference allows pretty accurate map placement, in theory it should be possible to go one step further and overlay the pins onto an augmented reality-style display. The idea would be to whip out your iPhone / Android device, point in the direction of the building in front of you and know at a glance whether it was listed or not. Then with another level of access into the back-end data (which English Heritage don’t appear to offer though any kind of API, yet) you could easily display the information that they hold about the structure.
I’m going to continue to polish up the various rough edges over the next few days, and then post the results up. I haven’t dug into the data’s usage conditions enough to know whether it would be possible to offer an iPhone app via the App Store, but assuming there’s no roadblocks to this I might give it a go. And it’ll be available for anyone who wants to try it in a beta form.
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Sinatra is really fun to work with. It's small and fast. It doesn't make many assumptions. If something goes wrong, it's pretty easy to go into the source and figure out what is going on.
There were a couple projects I wanted to take for a spin: Sinatra, Datamapper, HAML, and SASS. I decided to roll them all up into one proof-of-concept project. I don't go into a lot of depth on each, just enough to know that I can get it all up and running.
Also, since I'm running Passenger on some production boxes now, I wanted to deploy my Sinatra/Datamapper app through Passenger's Rack support.
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Converter for eastings/northings to lat/long
