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  #1 (permalink)  
Old 11-27-2009, 11:58 AM
Rune Allnor
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Default Tutorial on UTM coordinates?

Hi all.

I am working with some data that contain UTM positions.
The problem is that I need the UTM coordinates on centimeter
precision, which means I need some 8 or 9 significant digits
in the UTM coordinates; a few digits too many to make the
coordinates fit into a single-precision floating point number.

On the other hand, the position data I work with vary only on
the order of kilometers, so the single-precision floating point
format is more than precise enough to do the stuff I want.
And yes. Savings in both speed and memory footprint are
significant motivations for making the effort to make due
with single precision.

Along with the data, there comes a UTM Zone designation.

The question is if I can use this UTN Zone designation to
somehow derive a reference UTM position, and use relative
offsets from this reference position instead of the full positions?

Rune
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  #2 (permalink)  
Old 11-27-2009, 04:50 PM
Tim Wescott
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Default Re: Tutorial on UTM coordinates?

On Fri, 27 Nov 2009 03:58:12 -0800, Rune Allnor wrote:

> Hi all.
>
> I am working with some data that contain UTM positions. The problem is
> that I need the UTM coordinates on centimeter precision, which means I
> need some 8 or 9 significant digits in the UTM coordinates; a few digits
> too many to make the coordinates fit into a single-precision floating
> point number.
>
> On the other hand, the position data I work with vary only on the order
> of kilometers, so the single-precision floating point format is more
> than precise enough to do the stuff I want. And yes. Savings in both
> speed and memory footprint are significant motivations for making the
> effort to make due with single precision.
>
> Along with the data, there comes a UTM Zone designation.
>
> The question is if I can use this UTN Zone designation to somehow derive
> a reference UTM position, and use relative offsets from this reference
> position instead of the full positions?
>
> Rune


Hey Rune:

You need to drink your coffee -- I think this is easier than you think it
is, but I can't say because it's not entirely clear what you're doing.

You mention data in centimeter precision, then you mention data in
kilometer precision. Are you trying to say that you're being presented
data in cm, but you only need to keep data in km? If so, what about
simple truncation?

I just skimmed the Wikipedia entry on UTM, and it looks (in principal at
least) to be dead easy as long as you know what the reference meridians
are for each longitudnal zone. Are there subtleties that I'm not seeing
(which there shouldn't be for a system designed to make the math easy)?
Or do you need to drink another cuppa?

--
www.wescottdesign.com
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  #3 (permalink)  
Old 11-27-2009, 05:08 PM
Rune Allnor
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Default Re: Tutorial on UTM coordinates?

On 27 Nov, 17:50, Tim Wescott <[email protected]> wrote:
> On Fri, 27 Nov 2009 03:58:12 -0800, Rune Allnor wrote:
> > Hi all.

>
> > I am working with some data that contain UTM positions. The problem is
> > that I need the UTM coordinates on centimeter precision, which means I
> > need some 8 or 9 significant digits in the UTM coordinates; a few digits
> > too many to make the coordinates fit into a single-precision floating
> > point number.

>
> > On the other hand, the position data I work with vary only on the order
> > of kilometers, so the single-precision floating point format is more
> > than precise enough to do the stuff I want. And yes. Savings in both
> > speed and memory footprint are significant motivations for making the
> > effort to make due with single precision.

>
> > Along with the data, there comes a UTM Zone designation.

>
> > The question is if I can use this UTN Zone designation to somehow derive
> > a reference UTM position, and use relative offsets from this reference
> > position instead of the full positions?

>
> > Rune

>
> Hey Rune:
>
> You need to drink your coffee -- I think this is easier than you think it
> is, but I can't say because it's not entirely clear what you're doing.
>
> You mention data in centimeter precision, then you mention data in
> kilometer precision. *Are you trying to say that you're being presented
> data in cm, but you only need to keep data in km? *If so, what about
> simple truncation?


I'm working in cm precision in areas of size km x km.

> Or do you need to drink another cuppa?


Probably. Another couple of cans... of the espresso
strength stuff.

Rune
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  #4 (permalink)  
Old 11-27-2009, 05:28 PM
Tim Wescott
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Default Re: Tutorial on UTM coordinates?

On Fri, 27 Nov 2009 09:08:23 -0800, Rune Allnor wrote:

> On 27 Nov, 17:50, Tim Wescott <[email protected]> wrote:
>> On Fri, 27 Nov 2009 03:58:12 -0800, Rune Allnor wrote:
>> > Hi all.

>>
>> > I am working with some data that contain UTM positions. The problem
>> > is that I need the UTM coordinates on centimeter precision, which
>> > means I need some 8 or 9 significant digits in the UTM coordinates; a
>> > few digits too many to make the coordinates fit into a
>> > single-precision floating point number.

>>
>> > On the other hand, the position data I work with vary only on the
>> > order of kilometers, so the single-precision floating point format is
>> > more than precise enough to do the stuff I want. And yes. Savings in
>> > both speed and memory footprint are significant motivations for
>> > making the effort to make due with single precision.

>>
>> > Along with the data, there comes a UTM Zone designation.

>>
>> > The question is if I can use this UTN Zone designation to somehow
>> > derive a reference UTM position, and use relative offsets from this
>> > reference position instead of the full positions?

>>
>> > Rune

>>
>> Hey Rune:
>>
>> You need to drink your coffee -- I think this is easier than you think
>> it is, but I can't say because it's not entirely clear what you're
>> doing.
>>
>> You mention data in centimeter precision, then you mention data in
>> kilometer precision. Â*Are you trying to say that you're being presented
>> data in cm, but you only need to keep data in km? Â*If so, what about
>> simple truncation?

>
> I'm working in cm precision in areas of size km x km.


It makes sense now.

I could see that if you have a _bunch_ of data all within one area then
you could define a one-km-square zone and do everything relative to the
center of that then you'd be doing pretty well. I could even see just
extending the UTM concept to zones of any size.

Of course, then you have to arrange your data so that should your zone
change you can represent it unambiguously -- but that's more of a
programming problem than a signal processing one.

--
www.wescottdesign.com
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  #5 (permalink)  
Old 11-27-2009, 06:10 PM
Rich Webb
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Posts: n/a
Default Re: Tutorial on UTM coordinates?

On Fri, 27 Nov 2009 03:58:12 -0800 (PST), Rune Allnor
<[email protected]> wrote:

>Hi all.
>
>I am working with some data that contain UTM positions.
>The problem is that I need the UTM coordinates on centimeter
>precision, which means I need some 8 or 9 significant digits
>in the UTM coordinates; a few digits too many to make the
>coordinates fit into a single-precision floating point number.
>
>On the other hand, the position data I work with vary only on
>the order of kilometers, so the single-precision floating point
>format is more than precise enough to do the stuff I want.
>And yes. Savings in both speed and memory footprint are
>significant motivations for making the effort to make due
>with single precision.
>
>Along with the data, there comes a UTM Zone designation.
>
>The question is if I can use this UTN Zone designation to
>somehow derive a reference UTM position, and use relative
>offsets from this reference position instead of the full positions?


If you haven't already run across it, one very hand app for working with
UTM and similar coordinate systems is the GEOTRANS tool from the NGA.
Comes with source and a BSD-style (use it but give credit) license.
http://earth-info.nga.mil/GandG/geotrans/

I haven't had to muck-about with anything but good old lat/lon recently
but when I was, this toolset was great. It probably doesn't specifically
address your question but could be a good independent check of your
results.

--
Rich Webb Norfolk, VA
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  #6 (permalink)  
Old 11-28-2009, 11:11 AM
Heinrich Wolf
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Posts: n/a
Default Re: Tutorial on UTM coordinates?

Rune Allnor <[email protected]> writes:

> Hi all.
>
> I am working with some data that contain UTM positions.
> The problem is that I need the UTM coordinates on centimeter
> precision, which means I need some 8 or 9 significant digits
> in the UTM coordinates; a few digits too many to make the
> coordinates fit into a single-precision floating point number.
> ...


As Tim already said: there should be no big problem. I dealt with
transformations between geographical and Gauß-Krüger (UTM up to
normalizations) coordinates about a decade ago and found the math
quite easy for someone familar with complex analysis. Here is what I
remember:

Given geographical coordinates on the ellipsoid. Then first problem
is calculating the length of an arc of an ellipse which gives you GK
(Gauß-Krüger Koordinaten) for the middle of the zone. Integration is
done by expanding the integrand.

The characteristic requirement for GK is that they are obtained by a
conformal (theory of functions!) mapping from geographical
coordinates. This means, the mapping is complex differentiable and
thus it is sufficient to know it on the middle meridian of the zone,
which we have already got. Thus seems clear you can use local
coordinates for the inner calculations and transform between these and
UTM.

I remember that you need ten or twenty terms of the powerseries
expansion of the mapping to get it up to a centimeter. Calculating
the coefficients is messy and has been done and published in a paper
by the US Airforce.

--
hw
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  #7 (permalink)  
Old 11-29-2009, 05:41 PM
dalai lamah
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Posts: n/a
Default Re: Tutorial on UTM coordinates?

Un bel giorno Rune Allnor digitò:

> I'm working in cm precision in areas of size km x km.


Use floating point coordinates, but referred to the center of your zone of
interest. Removing the integer part of the coordinates (or most of it)
gives you a much better absolute resolution (in the mm domain, IIRC).

--
emboliaschizoide.splinder.com
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