[Freegis-list] Re: tool to find out lat/lon --> UTM

[Paul Ramsey]

Ah, yes, what you are not understanding is that sometime people want to 
project things into UTM zones that are outside the "valid" areas of the 
zone. And if proj automagically did zone determination that would break 
terribly. You have to think of each utm zone as a distinct map 
projection (as they are) and treat them that way. UTM is not one map 
projection, it is many.

P.

Cere Davis wrote:

> It's even easier than that to code with a simple mod function on the
> longitude value but it seems to me that the default dehaviour of proj would
> be to assume the zone you are in and give x-y values accordingly.  This is
> where I am confused...about the assumption.  Instead proj4 gives you x-y as
> if from GMT.  So I think it's something about zones that I don't
> understand.  
> 
> -Cere
> 
> Paul Ramsey wrote:
> 
> 
>>Write up 20 lines of perl to wrap around your proj4 call. The zone value
>>is a simple categorization on your longitude, so it is trivial to
>>script. Possibly why noone has bothered to make such a think automagic.
>>
>>P
>>
>>Cere Davis wrote:
>>
>>
>>>Hi everyone,
>>>
>>>I have sort of a basic GIS question that doesn't appear to be all that
>>>obvious to me.
>>>
>>>I am using the proj4 tools in linux to find at utm X-Y zone value for a
>>>given lat-lon value.  I have played around with it for a bit and I am
>>>suprised to find that proj requires me to input a default easting zero
>>>value (such as +lon_0=120w) in order to get meaningful x-y data for my
>>>zone.  To me this seems like redundant information.  If I give my lon_0
>>>value then I allready know what zone I am in basicly so this is not very
>>>usefull to me.  I suppose I could do some pre math and make some
>>>assumptions about the quadrant that my lat/lon value are in to find the
>>>lon_0 value before I send arguments to Proj but...  Is there any tool
>>>that just allows me to type in a lat/lon and returns a x-y and zone
>>>value?
>>>
>>>Thanks,
>>>-Cere
>>>
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>>>Freegis-list at intevation.de
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> 
> 
> 
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