| Re: problem in using function ll_to_utm.pro [message #60478 is a reply to message #60475] |
Tue, 20 May 2008 18:01  |
ben.bighair
Messages: 221
Registered: April 2007
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Senior Member |
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On May 20, 8:19 pm, Baikal <royou...@cnu.ac.kr> wrote:
> To all,
>
> I am a physical oceanographer who needs to use your idl program in my
> model output post-processing.
>
> While utilizing your utm conversion program (ll_to_utm.pro) in my
> research work, I have a problem due to zone change so that I encounter
> a discontinuity problems as follows;
>
> test_lon=[125.999,126.000] ; define test lon & lat
> test_lat=[36.000,36.000]
> ; test output
> for i=0,1 do
> print,i,test_lon(i),test_lat(i),ll_to_utm(test_lon(i),test_l at(i))
> 0 125.999 36.0000 770330.54 3988106.3
> 1 126.000 36.0000 229579.34 3988109.1
>
> I undrestand this is due to zone change from 51 to 52.
> I wonder how I can avoid this trouble in map drawing where my
> coastline data points lie over 125 to 127 E longitude.
>
> I appreciate your helps.
Hi,
I think I might have prepared that routine. To my understanding, you
don't want to work across UTM zones. My memory is a little rusty, but
I recall that the warping is minimized along central meridian of any
zone. I take that to mean that distortion is maximized along the
edges.
On the other hand, I suppose it is possible to offset the values in
one zone against the central meridian of the other - after all, the
origin of any UTM zone is some arbitrary value. You would have to
dive into the Snyder work referenced in the code. In any event, I
wonder why you are not mapping with your lat lon values directly. Why
bother going to UTM coords?
While we are at it, I have posted an update to that collection files -
in particular to UTM_ZONE so that it behaves a little better with
vectors of inputs. See ...
http://www.tidewater.net/~pemaquid/geo.zip
Cheers,
Ben
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