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  1. #1
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    Unanswered: Mapping / navigation in Transact-SQL

    Does anybody have a relatively easy way to calculate the longitude of that is N kilometers east/west of a given latitude/longitude location? I can handle the north/south latitude easily by computing it from the longitudinal meridian distance, but the east/west longitude is taxing my poor feeble brain.

    I'm trying to do this to create a stored procedure as a helper object for a completely home grown business mapping tool, so links to a web site that will do the job are plentiful but not useful!

    -PatP
    In theory, theory and practice are identical. In practice, theory and practice are unrelated.

  2. #2
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    easy no
    but it can be done
    have a look at movabletype
    requires trig functions
    I've used their equations in VB and Java and the accuracy is greater than 0.0001% on my tests

    just a thought, if Transact can't handle trig then would somehting like MySQL with the spatial extensions be a better bet
    Last edited by healdem; 04-16-13 at 19:00.
    I'd rather be riding on the Tiger 800 or the Norton

  3. #3
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    Aha, thank you! The Destination from Distance-Bearing calculation is exactly what I wanted.

    The best part is that I only have to compute it once for this purpose, since the points that I need are symmetrical, equal, and opposite.

    Now I can happily toddle off in search of a new problem!

    -PatP
    In theory, theory and practice are identical. In practice, theory and practice are unrelated.

  4. #4
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    Good luck with that. it works, but it can get a bit brain melting translating the equations into workign code, and then testing. I guess it depends on how much control you have of the incoming data. I tghink I got to over 1,000 unit tests just on the formats used in navigation NOT forgettign the others.

    FWIW bear in mind that:-
    1 degree of Latitude equates to 1 Nautical Mile AT SEA LEVEL
    although 1 nautical mile also equates to 1 degree of Longitude AT THE EQUATOR AT SEA LEVEL, it doesn't as you increase the latitude
    although I don't 'trust' Wikipedia this seems about right
    Code:
    Deg     Lat             Long		
    0	110.574 km	111.320 km
    15	110.649 km	107.551 km
    30	110.852 km	96.486 km
    45	111.132 km	78.847 km
    60	111.412 km	55.800 km
    75	111.618 km	28.902 km
    90	111.694 km	0.000 km
    those assumptions work at SEA LEVEL, at a different altitude 1 degree of Latitude will vary. if your proposed app assumes level flat ground then whatever error is introduced because of altitude will be consistent, but if there are significant differences in altitude over the plane then there could be additional variation.

    if you are looking for a bounding box you should be fine, a bounding circle can be tricky as strictly speaking it should be an ellipsoid
    but if you accuracy requirements are not critical it should be fine. by critical I mean sub 5m
    I'd rather be riding on the Tiger 800 or the Norton

  5. #5
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    For these purposes, 5km is never significant and 10km is only significant a few times per day. 25 Km is always significant.

    -PatP
    In theory, theory and practice are identical. In practice, theory and practice are unrelated.

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