We have been using the YDN Geo API for a while to provide approximate distances between locations. Recently we used the same integration to provide specific distances with a far higher degree of accuracy. We found that the API gives inaccurate locations for UK postcodes however the bug is straightforward to fix. The bug would appear to be related to the difference of the datum type from OSGB36 to WGS84. Changing the datum of the long/lat to WGS84 corrects the issue. The Ordnance Survey uses ‘OSGB-36’, based on an elliptical model of the earth’s surface which is a good fit to the UK. GPS systems generally use the world-wide ‘WGS-84’, based on an elliptical model which is a best approximation to the entire earth. At Greenwich, these differ by about 126m.
For anyone else, this takes a few minutes to fix when the data comes through. If this is an actual issue it would be good if Y! said when they were going to fix it as our fix will break our app.
We have been using the YDN Geo API for a while to provide approximate distances between locations. Recently we used the same integration to provide specific distances with a far higher degree of accuracy. We found that the API gives inaccurate locations for UK postcodes however the bug is straightforward to fix. The bug would appear to be related to the difference of the datum type from OSGB36 to WGS84. Changing the datum of the long/lat to WGS84 corrects the issue. The Ordnance Survey uses ‘OSGB-36’, based on an elliptical model of the earth’s surface which is a good fit to the UK. GPS systems generally use the world-wide ‘WGS-84’, based on an elliptical model which is a best approximation to the entire earth. At Greenwich, these differ by about 126m.
For anyone else, this takes a few minutes to fix when the data comes through. If this is an actual issue it would be good if Y! said when they were going to fix it as our fix will break our app.
Great API - many thanks Yahoo
Geographic coordinates returned by GeoPlanet are in the WGS84 datum as that datum is a global standard (and used for GPS systems around the world). You will need to translate these coordinates to the datum required by your application, if necessary.
I've seen this too. It is possible Yahoo have interpreted the co-ordinates as WGS-84 (because they looked decimal) whereas the data source may have used a different datum, OSGB-36. Maybe Yahoo could look into this?
