Utm

[+Geosophers]

If I have a UTM position and I'm asked to move 116m West and 1005m North for instance. Do I simply add the meters to my current UTM position or do I have to do special calculations to take into account the planet's curvature?

 

Thanks

Edited December 5, 2003 by Geosophers

[+Ish-n-Isha]

If I have a UTM position and I'm asked to move 116m West and 1005m North for instance. Do I simply add the meters to my current UTM position or do I have to do special calculations to take into account the planet's curvature?

 

Thanks

I have been told that UTM assumes a flat earth. So no special caclulations needed.

[+Dagg]

Hmm I wonder what cache your doing

[+PDOP's]

If I have a UTM position and I'm asked to move 116m West and 1005m North for instance. Do I simply add the meters to my current UTM position or do I have to do special calculations to take into account the planet's curvature?

 

Thanks

Yes if you're staying within the same UTM zone. It gets complicated when you cross the boundary into another zone.

[+Team GPSaxophone]

Isn't UTM only good for small (relatively-could be several dozen square miles) area? If you move a large distance, you'll be using a different grid

[+Team GPSaxophone]

zone...yeah...you said that as I was typing

[+Geosophers]

Thanks for the responses. It seems to me that it would be a nice to have a section in geocaching.com that would deal with the more technical aspect of the game. It could cover stuff like the subject of this discussion, WAAS, DGPS, etc. While this forum is extremely usefull, I think it would be nice to have it on geocaching.com also. What do you think?

[+nincehelser]

It's already here:

 

http://forums.Groundspeak.com/GC/index.php?showforum=11

 

Georeg

[Kiwi cruiser]

OMG...you mean the earths NOT flat!

[+nincehelser]

OMG...you mean the earths NOT flat!

Do not be alarmed. Go here and read the FAQ for the "truth".

 

http://www.flat-earth.org/

 

George

[bug and snake]

UTM stands for Universal Transverse Mercator and is a system (one of many) used by surveyors, navigators, cartographers and others to allow the curvature of the earth to be displayed on a flat sheet.

To answer your question, the distortion becomes greater as you move further from the central meridian of the zone in which you are working. Professionals, using the grid for mapping etc, would apply a scale factor to those offsets and also a correction to the bearing for the skew factor. However, the magnitude of the distances that you have mentioned are such that you would most likely be just fine using them as quoted. (assuming that this is a cache related question and not a national grid marker you are placing!)

[+gnbrotz]

In the example you initially gave, you mentioned moving 1005 meters north.

 

*Incorrect info removed from post

 

Depending upon your origin point, moving even 1m in a given direction may cause you to change zones.

 

If it were me, (based on your example) I'd use the "project a waypoint" feature on my gps to first project a waypoint the proper distance in one direction, then using that point, project a second one with the proper distance in the other direction. This would save calculating the length/angle of the hypotenuse yourself, though some might actually prefer doing it that way.

 

BTW, This all seems perfectly solid to me, but as it's 1:30 am where I am, I'm open to correction if I've mis-stated any of this.

Edited December 6, 2003 by gnbrotz

[bug and snake]

In the example you initially gave, you mentioned moving 1005 meters north. Since a UTM grid is only 1000m x 1000m, this would mean you would be changing zones, so just adding the values on to existing ones wouldn't work. Also, depending upon your origin point, moving even 1m in a given direction may cause you to change zones.

 

If it were me, (based on your example) I'd use the "project a waypoint" feature on my gps to first project a waypoint the proper distance in one direction, then using that point, project a second one with the proper distance in the other direction. This would save calculating the length/angle of the hypotenuse yourself, though some might actually prefer doing it that way.

 

BTW, This all seems perfectly solid to me, but as it's 1:30 am where I am, I'm open to correction if I've mis-stated any of this.

With due respect, I suggest you look here.....

UTM Zones

As with any mapping system a grid can be any size that you wish it to be.

[+gnbrotz]

Duly noted. I knew I was in no state to rationally think this out. That is an excellent link, and one I have actually seen before. I was thinking of the small grids on a topo map that I actually use to navigate with, rather than the actual size of the zone. I stand corrected, though the method I would use to determine the point in question remains the same.

 

Is there another (better) way to do what is being asked?

[bug and snake]

Duly noted. I knew I was in no state to rationally think this out. That is an excellent link, and one I have actually seen before. I was thinking of the small grids on a topo map that I actually use to navigate with, rather than the actual size of the zone. I stand corrected, though the method I would use to determine the point in question remains the same.

 

Is there another (better) way to do what is being asked?

The method is irrelevant - use any way that sits well in your head and is sound - just get the math right (trig, geometry, arithmetic, what ever) and you will arrive at the right place.

Also, note that with simple offsets and/or a range and bearing, crossing zone to zone is not relevant either. Until the question of false origins (used for convenience to avoid HUGE numbers) comes into the equation, the zone question is unimportant. (with the magnitudes under discussion here)

[+fizzymagic]

If I have a UTM position and I'm asked to move 116m West and 1005m North for instance. Do I simply add the meters to my current UTM position or do I have to do special calculations to take into account the planet's curvature?

The problem is not so much in your doing corrections for the curvature of the Earth as it is in defining "North."

 

Since the coord was given in UTM, then you can move that many meters in UTM and I'm sure you'll get the right answer.

 

But as you get away from the center of a UTM zone, the UTM "north" direction and true north become different. That would be the cause for any error over such a short distance.

 

If you want to play with the numbers, go grab my Geocalc progam here and convert the UTM to lat/long, do the projections, and translate back. That will give you an estimate of the difference.

 

If you'll post the UTM coords and the distances, I'll be glad to do that for you.

[+erik88l-r]

I designed a multistage cache hunt that moves you directly north in meters up the 84th meridian.

 

http://www.geocaching.com/seek/cache_details.aspx?ID=89798

 

What I found interesting as I learned about UTM the hard way is that the UTM coords did change predictably as one went north, and provided a great aid to the cache hunters. However the UTM longitude equivalent of 84° did not prove to be a constant even within the same UTM zone. It turns out that in many places the zone changes at a county line. As the county line is not a straight north-to-south line, neither is the UTM "easting". Luckily the "northing" component is measured from the equator, so that is a constant.

 

I learn something new everyday in this sport.

 

~erik~