comp.lang.idl-pvwave archive: archive » Algorithm for lat/lon searching

Home » Public Forums » archive » Algorithm for lat/lon searching

Show: Today's Messages :: Show Polls :: Message Navigator
E-mail to friend

Re: Algorithm for lat/lon searching [message #49880 is a reply to message #49807]

Fri, 18 August 2006 15:28

Terence
Messages: 2
Registered: August 2006

Junior Member

Can I suggest building two tables of the globe, which maps surface area
units as a small number of very approximately square areas (except near
the poles when they could become triangular)? The two tables refer to
two sets of such maps that overlap so that the centre of one area is on
the boundary of a similar area of the second map.
The northern and southern triangles are just displaced by longitude in
a similar relationship.

You build your two tables of the globe as area numbers which
corresponding to a numbering of the centre points based on known
latitude and longitude. Now you take your table of lat/lon points data
and assign the two individual map area numbers to each point on one
pass by rounding and truncating the exact coordinates so that the
high-order digits match the area centre lat/lon numbers and allow
direct assignment of the areas they have in common.

On a second pass, all numbers with the same index in either mapping are
close neighbours. If both indices are identical they are very close
neighbours within half an area unit. You choose a mapping resolution
suitable for the work to be done

Then you could order the data points by the new index numbers and so
process the globe data in a sequential manner that treats neighbouring
points in order.

Terence Wright

Report message to a moderator

[Message index]

		Algorithm for lat/lon searching By: Paul Van Delst[1] on Fri, 18 August 2006 07:50
		Re: Algorithm for lat/lon searching By: Bob Walton on Sat, 19 August 2006 20:18
		Re: Algorithm for lat/lon searching By: Terence on Fri, 18 August 2006 15:28
		Re: Algorithm for lat/lon searching By: K. Bowman on Fri, 18 August 2006 14:35

Previous Topic:	another request for help with getting rid of for loops...
Next Topic:	IDL Dataminer and MySQL problem

-=] Back to Top [=-

[ Syndicate this forum (XML) ] [

] [

]

Current Time: Wed Oct 08 19:05:46 PDT 2025

Total time taken to generate the page: 0.00414 seconds