In the run up to our new OxPoints system being launched, we’ve started to update some of our data and at the same time we’re attempting to make it just a little bit more accurate. Our basic data will be comprised of the main pedestrian and disabled (if different) entrances to each of the buildings we choose to record. Unfortunately recording the location of entrances is fairly difficult using standard GPS devices and our experience with a variety (more on that in another post) showed that nothing we already owned did the job particularly well. So we set our sights on aquiring a new device, namely a Garmin eTrex Vista HCx which would hopefully give an appropriate level of accuracy by means of having a high sensitivity chipset, being able to automatically average multiple readings and being EGNOS/WAAS enabled.
So far the results have been relatively consistent and a fair bit easier to record over previous devices but we now have a different problem – which map is correct? Below are screenshots of the same latitude and longitude (51.75982, -1.25724) shown on different mapping sources. I was actually standing on the red cross as shown in the first picture.
Now the question is, do we align our co-ordinates with a satelitte imaging source such as Google or Microsoft or do we leave our data ‘raw’? It seems that leaving our data raw seems to be the ideal method of ensuring consistency, but then the problem then lies with our users who will probably use a third party mapping source to overlay our data onto thus giving locations which are not entirely correct. We could of course correct for this verbosely by adding metadata to each location, but it seems to defeat the point. Opinions would be welcome!