Confusd about Coordinate Systems

[+FunYet]

OK. One of the things I’m determined to do this year is REALLY learn how to use a map and how to use a GPS, just for fun. I’ve always found these fascinating but never took the time to learn. I recently bought A Magellan Platinum and am getting the hang of it. I also bought a few topographic maps of my area and have been working with plotting GPS coordinates to the map with decent success. I even went out looking for my first Geocache this morning on the way to work. I didn’t find it (ran out of time) but I know I was within a few hundred feet, I was proud of myself for even getting to the right side of town based on coordinates. Anyway, here’s a question which I know is simple, but…

 

I understand the DEG/MIN/SEC format:

 

When MINutes reaches 60 then 1 is added to degree

When SEConds reaches 60 then 1 is added to MIN

 

Where I get lost is:

 

DEG/MIN.MM

And

DEG/MIN.MMM

 

What does .MM and .MMM signifiy, and at what point do they roll over and add 1 to the value of the unit to its left?

 

Does this question make sense??? Any good online sources of info that explain the differences between the different systems?

 

I have a couple of books I’m working with and I have a book on GPS, but it just mentions that the different formats exist, without telling much more about it.

 

Any help appreciated.

 

Thanks!

[Tahosa and Sons]

Lat & Long are only useful for sailors at sea who have long distances to travel.

To make a map and GPS talk to each other you would be wise to learn how to use UTM'S. Know the difference and meanings of Datums & Formats.

If you have a good software program, National Geographic TOPO is my preference. you can do wonders with UTM'S and your GPS. For UTM's here are some links that may help you:

http://edu-observatory.org/maps/utm.html

http://www.maptools.com/UsingUTM/index.html

And for General Knowledge about compass and such:

COMPASS & LAND NAVIGATION LINKS:

http://mcmcweb.er.usgs.gov/topomaps/

http://www.learn-orienteering.org/old/

http://www.netside.com/~lcoble/dir9/land_nav.htm

http://www.princeton.edu/~oa/manual/mapcompass.shtml

http://www.suunto.com/pls/suunto/suunto2.pubmainpage.frameset

http://www.brunton.com/

http://www.geocities.com/magnetic_declination/

http://www.ngdc.noaa.gov/cgi-bin/seg/gmag/fldsnth1.pl

http://edu-observatory.org/maps/utm.html

http://mac.usgs.gov/mac/isb/pubs/factsheets/fs03501.html

 

Tahosa - Dweller of the Mountain Tops.

[Jomarac5]

I would highly recommend the book GPS Made Easy by Lawrence Letham. It's very good.

[+mattb5]

First off, awesome resources!

 

The simple answer to the .MMM question is

.MMM is just the decimal portion of minutes - instead of figuring it in seconds. So when that hits .999 it rolls over to the next minute.

 

42 deg 21.500 min = 42 deg 21 min 30 sec

 

The DDD MM.MMM seems to be the pretty much agreed upon standard here.

[+EraSeek]

quote:

---

Originally posted by Tahosa:

Lat & Long are only useful for sailors at sea who have long distances to travel.

.

---

 

Gee, I gotta disagree with that one! All I or most others use is Latitude and Longitude. The statement should read ''UTM is only good for short range navigation and thus rather limited''. I might add that it is for those who still think the Earth is flat.

 

[GPSCache]

I enjoy using UTM. It is measured by meters-thus you can have the accuracy to a meter.. If your GPS has accuracy higher than that-then good for you!

 

Oh yeah

[Kerry.]

Lat&Long / UTM or whatever can really be meaured in whatever one wants to measure things in, it really doesn't make that much difference.

 

However just because it's UTM why does it have metre accuracy , bit of a myth that one. Accuracy is one thing and precision is totally another.

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

[+writer]

quote:

---

Originally posted by EraSeek:

All I or most others use is Latitude and Longitude. The statement should read ''UTM is only good for short range navigation and thus rather limited''. I might add that it is for those who still think the Earth is flat.

 

---

 

Anything you can do with lat/lon for geocaching (or general navigation, for that matter) is possible with UTM, and more easily, in my opinion. And lat/lon-based maps are also distorted, if for no other reason than they have distance scales.

[+jonboy]

Plotting from a GPS to a USGS map can be tricky. First off, most USGS quads don't have grid lines across them, so if you want to plot on it you will want to draw the grid line in using the hash marks on the edge of the map. The black hash marks are UTM lines and the blue ones are Lat & Long. I would recommend that you use UTM to make a map plot, as that system divides the map into rectangles with straight edges, where as Lat and long grid boxes have curved lines (the earth is not square and Lat & Long measures angles from the equator and from the Greenwich Meridian) and are almost impossible to draw.

 

Next you will want to make sure that your map and GPS are using the same datum. All but the very newest USGS quads use NAD27 datum, while all our Geocaching is done in WGS84. You change need to the datum on your GPS each time you want to make the transfer. You do that in the Setup portion of your GPS menu. At the same time, you will probably want to change coordinate systems from h.ddd.mm.mmm ( Hemisphere, degrees, minutes, decimal minutes) to UTM (there are more than one, make sure you choose UTM UPS).

 

UTM is plotted as easting and northing ( that is across from the left corner and up). You will want a UTM grid reader tool. You can buy one for the scale you are using, or you can make one using the metric scale bar at the center bottom of the quad. You hold the edge of a piece of paper against this scale bar, and tick off the hundred meter increments. This edge of paper becomes your grid reading tool. You will have to interpolate (guess) to get the ten meter digit. You can't expect to plot to more than ten meter accuracy. The number you get off the GPS will read some thing like 11 T 564576 E 4829733 N. Notice that there is one more digit for the northing than the easting. The only numbers you will be worrying about are the last three of each coordinate pair, the others can be read off the edge of the map. These two sets of three digits will locate you within a given 1,000 meter grid square.

 

There, isn't that simple? And there is a lot more I didn't cover. I like the www.maptools.com link mentioned above.

[dsandbro]

If you really want to split hairs:

 

Lat long is a spherical grid system, not a projection. OK, OK, the earth is not a sphere, but an irregular oblate spheroid. Now we are really getting into the trivia of geodesy.

 

UTM is a projection -- 'Universal Tranverse Mercator' if you really want to impress people at the next geocache event. Use that term and really wow 'em.

 

As a spherical grid system the dimensions of one unit (degree,minute,second) of longitude varies with latitude. It is not constant. One unit of latitude is not the same distance as the corresponding unit of longitude

 

One unit of UTM (one meter) is a meter regardless of where you are. It is a constant in both the x and y directions.

 

Within the UTM there is distortion as with all projections (All projections have distortion. It is impossible to have a distortion free projection). The least distortion is when you are close to the central meridian of that zone, the most when you are near the edges of the zone. Different projections distort in different ways. The amount of distortion in a small geocache search area is negligible. Even the distortion from one edge of a 15 minute USGS quad to the other can be disregarded by the average user.

 

Lat long works best for long range navigation like aircraft or ocean vessels. Use UTM for small distances like from the parking spot to the cache.

 

========================================

Friends don't let Friends geocache drunk.

[+Poindexter]

Lat/Lon is an Angular Coordinate system.

UTM generally refers to a rectangular grid coordinate system, not a projection.

I think you'll find through experience, as I have, that when working with USGS 7.5 minute quads, the UTM system is much easier to work with. Most of these topo's are in a Polyconic Projection. Many California topo's are in the Albers Projection. If you download your own USGS DRG's, you can easily add the UTM grid electronically (Iv'e seen the grid tic marks in error as much as 15 meters) as well as seamlessly join adjacent quads together. See my help page for info and links.

 

Poindexter

www.geocities.com/fairbank56

 

[This message was edited by Poindexter on February 01, 2003 at 07:11 PM.]

 

[This message was edited by Poindexter on February 01, 2003 at 07:15 PM.]

[+SearchRescueDog]

A really good place to start is The Maptools Website they have a good set of FAQs regarding datums and grid systems as well as the pros & cons of each.

 

When caching I hold my map & compass more then my GPS. I use UTM and USGS maps (printed from MAPTECH). I think it is a lot easier to hold up a UTM reader real quick than it is using a lat/long ruler (this is what makes it the staple grid system for inland search & rescue). Besides how else could you have this much fun converting WGS 84 to NAD27 and then from DM.MMM to UTM?

[+Poindexter]

I agree, the maptools site is an excellent web site. They do however make one false claim about USGS topographic maps and that is that they will always be in NAD27 datum. This is not the case as many newer ones are in NAD83.

 

Poindexter

[Kerry.]

quote:

---

Originally posted by Poindexter:

.... They do however make one false claim about USGS topographic maps and that is that they will always be in NAD27 datum. This is not the case as many newer ones are in NAD83.

---

 

Mixed chart/map datum's will be a problem in many countries untill ALL are eventually converted along a common WGS84 theme.

 

In the interim this issue is just another source for possible error as well as a issue for the map makers who have to extend the map sheets (in the interim) on the 2 sides where coverage falls short due to the different map datum's.

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

[dsandbro]

The Federal land agencies almost always use UTM projection, NAD27 in geographic data because all the historical data is in that format. Different states use different projections/datums to suit their local needs. Local governments frequently use WGS84 or NAD83 because they are relative newcomers to the mapping/GIS technology so they just started out using the latest standards. California state agencies use a variation of the Albers projection called the Teale projection for statewide data. Drives people nuts when swapping data across agencies. Fortunately, software easily converts one to the other with a couple of mouse clicks.

 

Lat long is really unsuitable for small area (< a single county) mapping and geospatial analysis. Most people like UTM for these purposes. With UTM the X,Y, and Z coordinates are all in the same units and calculations are easier in the field.

 

========================================

Friends don't let Friends geocache drunk.

[+Rygel]

FunYet,

 

You are not alone.

 

I'm confused about the format used on this site versus what Mapquest wants you to put in. It seems this site uses a hybrid of degrees/minutes and decimal, while Mapquest wants either all degrees/mintues/seconds or all decimal.

 

I'm new to this and I suck at math so I can't figure out how to convert!

[+yumitori]

quote:

---

Originally posted by Rygel:

FunYet,

 

You are not alone.

 

I'm confused about the format used on this site versus what Mapquest wants you to put in. It seems this site uses a hybrid of degrees/minutes and decimal, while Mapquest wants either all degrees/mintues/seconds or all decimal.

 

I'm new to this and I suck at math so I can't figure out how to convert!

---

 

Multiple (or divide) by 60. In other words, to convert N 46* 39.567' into degrees, minutes and seconds, multiple the non-integer portion of the minutes by 60. You get N 46* 39' 34" (rounded). To get all decimal degrees, divide the minutes by 60 and get N 46.659* (again rounded).

 

Ron/yumitori

[+Rygel]

quote:

---

Originally posted by yumitori:

quote:

---

Originally posted by Rygel:

FunYet,

 

You are not alone.

 

I'm confused about the format used on this site versus what Mapquest wants you to put in. It seems this site uses a hybrid of degrees/minutes and decimal, while Mapquest wants either all degrees/mintues/seconds or all decimal.

 

I'm new to this and I suck at math so I can't figure out how to convert!

---

 

Multiple (or divide) by 60. In other words, to convert N 46* 39.567' into degrees, minutes and seconds, multiple the non-integer portion of the minutes by 60. You get N 46* 39' 34" (rounded). To get all decimal degrees, divide the minutes by 60 and get N 46.659* (again rounded).

 

Ron/yumitori

---

 

Thanks! I figured it was something simple like that!!

 

The great question...which I have not been able to answer, despite my thirty years of research into the feminine soul, is "What does a woman want?" --Freud