Re: [R] from long/lat to UTM

From: Ted Harding <Ted.Harding_at_nessie.mcc.ac.uk>
Date: Fri 11 Mar 2005 - 03:13:01 EST


On 10-Mar-05 Gabor Grothendieck wrote:

>  <Ted.Harding <at> nessie.mcc.ac.uk> writes:

>: [...]
>: As Sander says, "Not sure where you would derive the time zone!".
>:
>: Unless you can refer a (long,lat) position to a look-up
>: table, you can't predict what the zone will be to less
>: the 1 hour (except of course for the "nominal" time-zones
>: by 15deg sectors). I've never encountered a "digital"
>: version of such a table (my Atlas must be based on one,
>: though).
>:
>: Best wishes,
>: Ted.
> 
> The fBasics package of the rmetrics project uses the Olsen time
> zone data base which does take some of these things into account.

Thanks, Gabor! However, this seems to be just the usual sort of thing -- TimeZone name with corresponding TZ data. You first have to know the TZ name. (Unless I have overlooked sonething in the Olsen database).

What I had in mind was a "look-up" facility whereby a (long,lat) pair could be submitted as a query, returning the TZ region (name) within which that geographical point lay.

The only completely general mechanism I can think of would consist of

  1. a named list of boundary contours
  2. a function which, for each name in the list, returns the TZ name

Then, for instance, given a point P = (long,lat), the list could be searched by verifying, for each contour in the list, whether the point lay in the region circumscribed by the coutour (e.g. by computing the winding number for the contour with respect to the point). This would also work for regions with holes in them, provided the boundary of the hole was presented in the correct order of points (e.g. such that the region of which it was the boundary lies to the left as you go through the sequence).

If, for instance, I had the contour data for the TZ map in my Atlas, I could construct such a thing! But, as I say, I have not come across such a dataset. I'd be interested to learn of one, though!

Best wishes,
Ted.



E-Mail: (Ted Harding) <Ted.Harding@nessie.mcc.ac.uk> Fax-to-email: +44 (0)870 094 0861
Date: 10-Mar-05                                       Time: 16:13:01
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