Plotting Points-Latitude/Longitude
 

A trip to montana a while back got me interested in this sort of land nav. I bought a USGS map of the area we where in as a momento. Since MGRS is the only way of plotting points I was familiar with it got me to wondering how I could go about plotting cooridinates onto the map if it only had LAT/LONG markings. Had a gps at the time so I new the location of where we were but did not know how to plot the LAT/LONG from the GPS to the map, or plot where we wanted to go on the map and then punch it in the GPS. I thought this would be a neet trick to learn if I ever had to use any maps that did not use MGRS.

Here is what I found.

http://www.maptools.com/products/LatLonRulers.html (tools needed)

http://www.maptools.com/UsingLatLon/plotting.html (plotting and measuing LAT/Long)


Would this sort if info have any use? Have any of you found it neccessary to use foriegn maps that only had LAT/LONG? How handy do you think this trick could be?

regards

berdan

The conversion technique is taught, or used to be.

Yes, I have used it.

Conversion to MGRS is usually for ground types. The Navy and AF can work off either system, and on large scale maps, frequently do.

TR

Sir

Dont have one of those Lat/Long rules. Without trying it as I am reading the directions it sounds sort of complicated and time consuming. Is it?
What scale maps have you had to use this technique with the most?
Where did this technique use to be taught, basic level map and land nav or at more advanced levels?

regards

berdan

IIRC, USGS 1:24k maps have tick marks along the edges that one can use to draw MGRS grids onto the map, which in turn allow you to use MGRS plotting techniques. Wouldn't that be an easier solution?

Yes sir, it sure would. But respectfully, I can not believe it could be that convenient for all maps/scales one may come across.

1:24,000 1:25,000 1:50,000 1:62,500
1:63,360 1:65,000 1:69,500 1:77,000
1:80,000 1:84,000 1:100,000 1:125,000
1:126,720 1:150,000 1:156,000 1:160,000
1:182,000 1:190,000 1:200,000 1:250,000
1:300,000 1:320,000 1:400,000 1:500,000

Wouldnt those tick marks be for UTM? Is that the same as MGRS? I would still need to get a 1:24,000 ruler/protactor to plot points wouldnt I?


regards

berdan

Lat/Lon is not rocket science. They teach Navy E-1 QM (not the same as Army) types how to do it. It is still taught in the "Q" course. It's the universal standard. You can use it with any map, every edition, without converting UTM, MGRS, or any of about 20 other coordinate systems in use around the world. It's the only thing guaranteed (mostly) to work on HN maps. If that's how you have to navigate and you're stuck with a coalition warfare mission, you will be grateful for having learned it. If you want to do anything joint you probably have to learn it. If you're on AD and need to learn it or just refresh your memory look in FM 3-05.212 Special Forces Waterborne Operations. It has a pretty good explanation of the technique. FWIW - Peregrino

Edited to add: You don't need to spend your money on the rulers if you just purchase an architect's scale and use the 10th's division IAW the instructions in the Map Reading (FM21-26) manual. The field expedient methods of creating a scale by marking a tongue depressor or cutting a latitude scale off of a nautical chart and pasting it on the tongue depressor are even cheaper and just as effective.

For those who may be interested, here's a link to download FM 3-25.26, Map Reading & Land Navigation .

as i shuffle through my mental rolodex, it seems that we made our own lat/long rulers in training group using a protactor...all you need is 60 evenly divided units that will fit diagonally across lines of latitude or longitude...

i work with maps from the USGS, USACE, USBOR, USBLM, USFS and a few from state agencies...every quad sheet i've come across, regardless of scale, has lat/long tic marks...i'm not saying they all do, i'm just saying that everyone i've come across in eleven years as a land surveyor, has...i use lat/long as often as possible...if i can put a project on a geodetic framework, i can give a client coordinates in just about any format, any system, ground, grid, geo-reference, Cartesian XYZ, you name it...

one thing to be aware of ...the older quad sheets will show lat/long in NAD 27 which is based on the Clarke Reference Ellipsoid of 1866...it was great for the northern part of the Western Hemisphere...it varies considerably from WGS 84 (the coordinates you get in a hand-held GPS) and/or NAD 83, which are both based on the Geodetic Reference System of 1980...this model is based on global attributes and is more accurate...

something else to be aware of, regarding the numbers associated with the tic marks on the margin of the map...some maps have UTM coords, some have State Plane Coordinate values, some have both...pay attention to that...at any rate, the projection should be listed (NAD 83 or NAD 27) on the map and if you are using a hand-held GPS, you should be able to toggle your coordinate system to one that matches your map...

lksteve

could you explain making own lat/long rules. Do you make one for each scale?
60 tic marks, and each tic would be diff min. and sec. for each scale?

regards

berdan

i wish we were in my office, i could draw a picture...basically, a degree is comprised of 60 minutes...that much we know...you want the ruler you create to be longer than a degree of longitude and longer than a degree of latitude...that way, you can slide the ruler along your projected lines of lat/long by placing the zero on the east side/south side and the 60 on the west side/north side...(that works well in North America...)remember this...even though the ruler is on a diagonal, the increments (those 60 tic marks) are evenly spaced, as the minutes that comprise a degree are evenly spaced...to determine latitude (your northerly position) the tic marks on the ruler are on the projected lines of latitude...to determine longitude (your easterly position), the tic marks are placed on the projected lines of longitude...the key is that the ruler has to be longer than the distance of one degree between lines of latitude and lines of longitude...it will work...

of course, you can always buy state map software from National Geographic and move the cursor to a point you are interested in and read the lat/long from the lower right corner of the screen...that's the way i do it nowadays...

1st draw the lat/lon lines on the map(s) you're using. Then select a straight edge that is longer than the distance between the latitude lines. Mark it with the 60 divisions. The scale that you constructed should be so long that it lays across the map at an angle. Lay it on the map with the extreme points touching the lat (or lon) lines. As the scale of the map changes, the angle of the improvised scale will also change. The only thing you care about is an equal division of the area which you will get this way - sort of like a parrallel ruler. Slide the scale L/R or U/D until one of the 60 tick marks touches the desired point. Count and interpolate for min/sec. Move to the other lat/lon reference line and repeat for the second half of the coordinate. Hope this helps.

Edited to add - What lksteve said! It always takes me too long to type.

depending on map scale, sometimes you can create a ruler that will allow you to calc seconds...not normal issue to a guy in the boonies...i can just imagine carrying a 1:12500 of the Schwarzes Pferd AO on a Flintlock...ruck would be full of map and wet socks...but i digress...something that might be helpful...take the time to figure out how far a second of longitude and latitude is where you are going to be hiking/camping/operating...that varies place to place...

interpolate...? musta been an 11C, huh? :D

Among other things! Got to admit it sounds better than SWAG. :D

SWAG usually works better, though... :D