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I have a bunch of objects which have associated Eastings and Northings in format OSGB36

for example:

265397  869562
547297  179002

If I have a starting Easting and Northing, and wanted to find related objects within X km is it possible to compute a Start/End Northing and Start/End Easting range that I can search for programatically?

I am using C#.

I.e. searching for objects using pseudo-code :

Easting >= 265390 && Easting <= 265400 &&
Northing >= 869560 && Northing <= 869564

would this find nearby objects? What resolution do these coordinates operate to? I can operate in miles or km, just need to know the scale - if such a thing is possible.

Sorry this is new to me.

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Further to Polygeo's comment, could you also say what coordinate reference system those eastings and northings are in? If UTM, which UTM zone? –  BradHards Apr 12 at 23:11
    
Sorry for lack of detail - edited post as requested. –  Phil Apr 12 at 23:25
    
See digimap.edina.ac.uk/webhelp/os/data_information/os_data_issues/… for help on precision of OSGB map refs. –  martin f Apr 12 at 23:40
    
Thanks Martin - that's really helped. –  Phil Apr 13 at 0:12

1 Answer 1

up vote 3 down vote accepted

See National Grid Reference Converter for help on the precision of OSGB map references.

If you just use a search range to create a box surrounding your query point, as indicated by

(east_QP - range)  <= east  <= (east_QP + range)
(north_QP - range) <= north <= (north_QP + range)

a variation on your pseudo code, it is fast but biased.

If you "create a circle" around your query point

hypot ((east_QP - east), (north_QP - north)) <= range

where hypot() computes distance, it is a tiny bit slower but less biased as it cuts out the box corners.

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Thanks Martin - very helpful –  Phil Apr 14 at 15:03

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