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LSUFan

Why so deep

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We attempted to recover CQ2753 triangulation station today. We were successful with it's two reference marks, one of which was at ground level, and the other one about 2 inches below the surface (the metal detector sniffed it out easily).

 

However, the station mark was not found. The description states that it is 18 inches below the ground surface. :ph34r: I have never encountered one like that before. Is there a reason it would be so deep?

 

The ground seemed to be all level, and according to the property owner, there has been no major excavations or anything there. I don't think my current metal detector will sniff that deep.

 

Thanks

Edited by LSUFan

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You should rejoice that you are not trying for the underground mark, at 42 inches below the surface! What's the water table level in that part of Louisiana? [Grin.]

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You should rejoice that you are not trying for the underground mark, at 42 inches below the surface! What's the water table level in that part of Louisiana? [Grin.]

 

Well, it has rained everyday now for about 3 weeks straight, so the water table is probably about ground level or higher in some places. :ph34r:

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It does seem a bit strange that a concrete post would be placed so far below grade. When I read you OP, I assumed the monumentation team dug down to put the mark in bedrock, but I guess not.

 

If you found the reference marks, a little measuring should have pointed at the location to start digging, eh?

 

EDITED: for speeling

Edited by AZcachemeister

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It does seem a bit strange that a concrete post would be placed so far below grade. When I read you OP, I assumed the monumentation team dug down to put the mark in bedrock, but I guess not.

 

If you found the reference marks, a little measuring should have pointed at the location to start digging, eh?

 

EDITED: for speeling

 

Yes, I tried that unsuccessfully. My compass isn't the greatest, but usually puts me close enough to finish it out with the metal detector. I even tried to line up off the reference marks, but the arrows on the disk didn't quite point to where the measurements from the road center and fence put it. It is in someone's front yard, and I don't want to push their generousity by digging holes in their yard.. I guess I will get a ground probe and go back. I almost thought about trying to use witching rods and see if I could find it. :ph34r:

 

Can you think of a reason for placing it so deep? We don't have anything near bedrock here, Just gumbo mud and more gumbo mud.

 

On another note, the property owner described what I believe was possibly a Bilby Tower being there at one time. I do see where the height of the light above the station was 35 meters. (another thing I have yet to encounter in my limited experience, one being so high)

Edited by LSUFan

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Besides measuring from roads etc for the general location, you should find the "box score" information on the NGS data sheet to give precise distance from each RM to the tri-station (in meters, multiply by 3.280833 for feet).

 

It was standard practice to place tri-stations on (at that time) cultivated land out of the road right of way, and to bury the disk deep enough to avoid the farmer plowing it out. Many such locations later became residences.

 

Even 18 inches wasn't always deep enough as the soil got moved around. On LE0530 we found the "surface" disk had been plowed out and the underground mark was only 29 inches down instead of an original approx 5 feet.

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Can you think of a reason for placing it so deep?

 

Cultivated field at the time the mark was set? Farm Land etc.

Property owner wanted it buried so he would not hit it with the plow.

 

I have found that before.

Edited by Z15

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It makes sense now. Many thanks to everyone for the education. I always appreciate it.

 

Now I can go to sleep knowing I'm not quite as dumb as I was when I woke up this morning. :ph34r:

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Besides measuring from roads etc for the general location, you should find the "box score" information on the NGS data sheet to give precise distance from each RM to the tri-station (in meters, multiply by 3.280833 for feet).

 

It was standard practice to place tri-stations on (at that time) cultivated land out of the road right of way, and to bury the disk deep enough to avoid the farmer plowing it out. Many such locations later became residences.

 

Even 18 inches wasn't always deep enough as the soil got moved around. On LE0530 we found the "surface" disk had been plowed out and the underground mark was only 29 inches down instead of an original approx 5 feet.

 

Use two tapes and measure in the general direction of the arrows.

Where the tapes cross at the correct measurements is where to dig.

It might be easier for one person to do this by tying the zero ends of the tapes together and then pinning each one at the correct measurement at the RM end. Pull both tapes tight and start digging.

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Hey that's not so deep, I was out benchmarking and just had to go take a look for NB1974 which somehow magically went from flush with ground in 1936 to 10 meters below ground in 1992.

 

NB1974 HISTORY - Date Condition Report By

NB1974 HISTORY - 1936 MONUMENTED NYGS

NB1974 HISTORY - 1969 GOOD CGS

NB1974 HISTORY - 19920529 GOOD USPSQD

NB1974

NB1974 STATION DESCRIPTION

NB1974

NB1974'DESCRIBED BY NEW YORK GEODETIC SURVEY 1936 (LRH)

NB1974'IN MENDEN, 0.45 MILE SOUTH OF RUSH-MENDON ROAD, 26 FEET WEST OF

NB1974'CENTER LINE OF WEST BLOOMFIELD-PITTSFORD ROAD, 214.8 FEET SOUTH

NB1974'OF CENTER LINE OF LEHIGH VALLEY RAILROAD MAIN-LINE ROADBED, 48.5

NB1974'FEET WEST OF EAST RIGHT-OF-WAY FENCE, 20 FEET NORTH OF

NB1974'INTERSECTION OF RIGHT-OF-WAY AND FARM FENCES, AND 4 FEET EAST

NB1974'OF WEST RIGHT-OF-WAY FENCE. STATION IS A U.S.C. AND G.S. AND

NB1974'STATE SURVEY STANDARD DISK IN CONCRETE FLUSH WITH GROUND.

NB1974

NB1974 STATION RECOVERY (1969)

NB1974

NB1974'RECOVERY NOTE BY COAST AND GEODETIC SURVEY 1969 (GWM)

NB1974'ORIGINAL DESCRIPTION INADEQUATE. NEW DESCRIPTION FOLLOWS--

NB1974'

NB1974'IN MENDON, ALONG WEST BLOOMFIELD ROAD

NB1974'

NB1974'0.45 MILE SOUTH OF RUSH-MENDON ROAD

NB1974'

NB1974'4.0 FEET EAST OF FENCELINE

NB1974'

NB1974'23.2 FEET WEST OF CENTERLINE OF WEST BLOOMFIELD ROAD

NB1974'

NB1974'20.1 FEET NORTH OF FENCE CORNER

NB1974'

NB1974'128.0 FEET SOUTH OF POLE RG AND E 128

NB1974'

NB1974'1.17 MILES WEST SOUTHWEST OF STATION LONE 1969

NB1974'

NB1974'STATION IS A U.S. COAST AND GEODETIC SURVEY AND STATE SURVEY

NB1974'STANDARD DISK IN CONCRETE STAMPED 1062, 1936

NB1974

NB1974 STATION RECOVERY (1992)

NB1974

NB1974'RECOVERY NOTE BY US POWER SQUADRON 1992 (AMW)

NB1974'THE FENCE NO LONGER EXISTS NEAR THE STATION. THE CORNER POST IS STILL

NB1974'THERE. THE MARK IS 3 FT (0.9 M) ESE OF A WITNESS POST. THE MARK IS

NB1974'ABOUT 10 M (32.8 FT) BELOW GROUND LEVEL AND WAS UNCOVERED.

 

Turns out it was only down about 6 inches due to some regrading I believe when the old railroad tracks were torn up to make way for the greenway trail.

 

Geocaching NB1974 Recovery

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Regarding taping from RMs, if you only have one tape, measure out the distance from the RM to the approximate position and mark the distance arc (from the RM) with a stick or such (if the area is not in some ones lawn, I kick out an arc 3 or 4 feet long). Then measure from the other RM and see where the distance intersects the stick (or kick mark). For holding the tape at the RM, you can sometimes use a long screwdriver and push it into the ground behind the RM and fasten the tape to the screwdriver.

 

Regarding buried station marks, here is the appropriate quote from USC&GS Special Pub. #247 “Manual of Geodetic Triangulation”, page 262:

 

“Where a station mark must be set on land subject to cultivation it is better to have the top of the post entirely below the depth which can be reached by a plow-that is, about 12 inches below the surface. Where a mark of this type is set it is necessary that measurements to the center of the roadways, section lines, etc., be made in sufficient number to enable one seeking to recover the mark in the future to determine its location within a few feet. The mark itself can then be found by digging or by prodding with an iron rod.”

 

Also, when this is done, the Reference Marks should be set in fence lines so that they can be set at the surface.

 

Years ago my boss sent me out to recover a mark on a farm. The triangulation station was set below the surface... and in the middle of a pig sty! We found the RMs, measured in, dug down, and found the station.

 

GeorgeL

NGS

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Use two tapes and measure in the general direction of the arrows.

Where the tapes cross at the correct measurements is where to dig.

It might be easier for one person to do this by tying the zero ends of the tapes together and then pinning each one at the correct measurement at the RM end. Pull both tapes tight and start digging.

 

Absolutely Brilliant! I see why you make the big bucks. :laughing: I can't wait to go back now. However it's raining cats and dogs here, AGAIN.

 

 

Regarding taping from RMs, if you only have one tape, measure out the distance from the RM to the approximate position and mark the distance arc (from the RM) with a stick or such (if the area is not in some ones lawn, I kick out an arc 3 or 4 feet long). Then measure from the other RM and see where the distance intersects the stick (or kick mark). For holding the tape at the RM, you can sometimes use a long screwdriver and push it into the ground behind the RM and fasten the tape to the screwdriver.

 

Regarding buried station marks, here is the appropriate quote from USC&GS Special Pub. #247 “Manual of Geodetic Triangulation”, page 262:

 

“Where a station mark must be set on land subject to cultivation it is better to have the top of the post entirely below the depth which can be reached by a plow-that is, about 12 inches below the surface. Where a mark of this type is set it is necessary that measurements to the center of the roadways, section lines, etc., be made in sufficient number to enable one seeking to recover the mark in the future to determine its location within a few feet. The mark itself can then be found by digging or by prodding with an iron rod.”

 

Also, when this is done, the Reference Marks should be set in fence lines so that they can be set at the surface.

 

Years ago my boss sent me out to recover a mark on a farm. The triangulation station was set below the surface... and in the middle of a pig sty! We found the RMs, measured in, dug down, and found the station.

 

GeorgeL

NGS

 

Yes George, that's exactly the way the marks were set. The two reference marks were near the road, where I imagine a fence line probably used to exist.

 

I have been been lucky so far in my searches for triangulation stations and have just about always found the station first, then measured the distance to the reference marks....set a temporary flag....and then used a metal detector to pinpoint. There was one, that I had to do reverse azimuths from the reference marks to the station, but it was fairly easy to locate.

 

Now thanks to the great advice that you and everyone has shared with me here, I will definitely change my techniques and should be successful in locating this station. I feel extremely confident now (famous last words). :ph34r:

 

I can't say enough times, how much I really appreciate the help from everybody.

 

Being I just do this for fun, I might have passed on one in a pig sty. :laughing:

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If you only have 1 tape measure and it is long enough you can easily pinpoint the station mark.

 

Anchor the end of the tape at the first RM, then anchor the tape at RM2 where the tape reads the combined length of distances for both RMs. If RM1 is 40.5 feet from the station and RM2 is 39 feet from the station, then anchor the tape at 79.5 at the second RM. You then go to the 40.5 feet mark on the tape (following the arrows on the RMs) and draw it tight. This will be the only spot where both measurements fit the description. You will be standing right where RM1 is 40.5 feet away and RM2 is 39 feet away. Use a probe (before digging) to verify that you measured correctly.

 

John

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If you only have 1 tape measure and it is long enough you can easily pinpoint the station mark.

 

Anchor the end of the tape at the first RM, then anchor the tape at RM2 where the tape reads the combined length of distances for both RMs. If RM1 is 40.5 feet from the station and RM2 is 39 feet from the station, then anchor the tape at 79.5 at the second RM. You then go to the 40.5 feet mark on the tape (following the arrows on the RMs) and draw it tight. This will be the only spot where both measurements fit the description. You will be standing right where RM1 is 40.5 feet away and RM2 is 39 feet away. Use a probe (before digging) to verify that you measured correctly.

 

John

Took me a moment to visualize that... and it's brilliantly simple!!

~ Mitch ~

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Use two tapes and measure in the general direction of the arrows.

Where the tapes cross at the correct measurements is where to dig.

It might be easier for one person to do this by tying the zero ends of the tapes together and then pinning each one at the correct measurement at the RM end. Pull both tapes tight and start digging.

 

 

Regarding taping from RMs, if you only have one tape, measure out the distance from the RM to the approximate position and mark the distance arc (from the RM) with a stick or such (if the area is not in some ones lawn, I kick out an arc 3 or 4 feet long). Then measure from the other RM and see where the distance intersects the stick (or kick mark). For holding the tape at the RM, you can sometimes use a long screwdriver and push it into the ground behind the RM and fasten the tape to the screwdriver.

 

 

If you only have 1 tape measure and it is long enough you can easily pinpoint the station mark.

 

Anchor the end of the tape at the first RM, then anchor the tape at RM2 where the tape reads the combined length of distances for both RMs. If RM1 is 40.5 feet from the station and RM2 is 39 feet from the station, then anchor the tape at 79.5 at the second RM. You then go to the 40.5 feet mark on the tape (following the arrows on the RMs) and draw it tight. This will be the only spot where both measurements fit the description. You will be standing right where RM1 is 40.5 feet away and RM2 is 39 feet away. Use a probe (before digging) to verify that you measured correctly.

 

Well, isn't this just great! Now, because of you smart guys, I have to go find Mrs. Johnson (my tenth grade geometry teacher) and apologize to her. I argued with her when I was 16, that I would never use the stuff she was teaching me in real life. Ya sure proved me wrong. I hope you are happy. :ph34r: LOL

Edited by LSUFan

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But what we have all overlooked is that the datasheet (box score) only gives a distance from RM 1! :D

 

With all this rain you are having, probing to 18" shouldn't be so difficult with the right tool.

It looks like you will be forced to probe in an arc from RM 1, and to concentrate in the zone where the arrow from RM 2 is pointing.

In my area, I would expect the angle formed by the RMs and the station mark to be about 90°.

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You are right, a missing distance makes it harder. Perhaps some compass work is in order to reduce the amount of arc to be searched.

 

The angles in the box score are degrees, minutes, and seconds run together without spaces, so 3331235.8 is 333 degrees 12 minutes 35.8 seconds, or about 333.2 degrees.

 

The angle formed in the tape using John's method (with unknown distance added on) is

115 53

037 59

-------

077 54 or 78 degrees to compass accuracy

 

If the Az mark is found, you can check your compass calibration against it since the reading to it won't change significantly for many feet around the station disk.

 

CQ2753| CY3281 ANDERSON RM 1 19.670 METERS 03759 |

CQ2753| CY3282 ANDERSON RM 2 11553 |

CQ2753| CQ2742 LUNA LOOKOUT TOWER APPROX. 7.3 KM 2382325.3 |

CQ2753| CY3280 ANDERSON AZ MK 3331235.8 |

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Just a few thoughts...

 

Looking at the datasheet and seeing two angles with a distance (length) given, I thought to myself that it was possible for the triangle formed

by the three marks to be solved using trig. However I got a headache trying to figure it out, as I was never really good at that in college.

When I sketched it out, I realized that there is only one angle and one length given, so it's impossible to solve.

If you go back and still can't find the station, try to take a measurement between RM1 and RM2. With one angle and two distances,

I think it's possible to determine the distance from RM2 to the station.

(Then ask Mrs. Johnson to solve the equations for you). :D

 

Not sure what metal detector you're using, but I have used a White's CoinMaster II which outperformed my White's Spectrum when it came

to copper and brass. A 3.5 inch disk presents a strong signal buried eighteen inches deep. See if your detector will read the reference

mark from a similar distance using an air test. Wet ground will help the ground conduct the signal, so the three weeks of rain is to your advantage.

(Back in my metal detecting days, I was able to retrieve an 1853 quarter at 9 inches on edge, but that's OT).

 

A good probe is easy to make and quite inexpensive. I bought a 3 foot stainless steel rod from the hardware store for less than $5

and epoxied it into the end of an old broom handle. Just rough up the glued end, round off the tip with a metal file and cut the handle to

a comfortable length. Mine does a nice job of probing and serves as a hiking staff when I'm out and about. I've used it to find a few

stations where metal detectors aren't allowed. With the wet ground in your area and an absence of large stones that would be expected

in a cultivated field, your chances of hitting the mark is pretty darn good.

 

I checked the magnetic declination in your area and it's about 1.25 degrees. The best you can do with a decent compass is about two degrees

or less, so a little practice with your compass will get you close enough to start probing or detecting.

 

The azimuth mark appears to be about 1/2 mile northwest of the station where a north-south fenceline crosses the road.

 

Let us know when you find it,

~ Mitch ~

 

Edited to add another random thought regarding magnetic declination and the azimuth mark.

Edited by Difficult Run

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I think I'd go for the easiest solution first and see if you are very lucky. It will help if there is another person to help stretch the tape and string, but it can be done solo.

 

Anchor your tape at the first RM and measure of the given distance to the station mark. Then anchor a piece of string at the other RM and stretch it out following the arrow on the second RM. Try to follow the direction of the arrow as close as possible. Then adjust the tape from the first RM to follow the arrow as close as possible and when the distance is correct start probing midway between the tape and the string.

 

We bought a cheap Gate valve key from True Value that looks similar to this one HIGVK36[1].jpg and we cut the "U" off the bottom and sharpened it to a point. It makes a great probe and only cost about $6 plus the time to modify the tip.

 

John

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Using an aerial photo of the area and applying, as best one can, the offsets of RM2 from the driveway and road (assuming they are the same driveway and road as they existed in 1971), I get 105 feet, more or less, from RM2 to the tri-station and a little more than 111 feet between RM1 and RM2. Of course these are very approximate.

 

If I went out there I think I'd start by measuring the distance between RM1 and RM2. If it was close to 111 feet I'd have more confidence in starting probing 105 feet NW of RM2 and 64.5 feet SW of RM1.

 

For what it's worth.

 

P.S. all the offsets for the tri-station, RM1, and RM2 seemed to match the aerial photo pretty well except the one that says the tri-station is 105 feet SW of the Road. Based on the adjusted coordinates of the tri-station, it appears to be more like 86 feet if they measured the shortest distance from the tri-station to the center of the road.

Edited by tosborn

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Using the azimuth to the AZ Mark, the offset from the center of Philpot Road, and the probable general location of the NS fenceline running on the SW side of the road, the Azimuth Mark is probably close to 32.40014N, 92.16405W. This also appears to agree with the 2.1 miles from the junction of Philpot Road and Highway 34 for the AZ Mark in the description. Again, for what its worth, considering that we're working from 2004 aerial photos.

Edited by tosborn

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........

Looking at the datasheet and seeing two angles with a distance (length) given, I thought to myself that it was possible for the triangle formed

by the three marks to be solved using trig. However I got a headache trying to figure it out, as I was never really good at that in college.

When I sketched it out, I realized that there is only one angle and one length given, so it's impossible to solve.

........

FizzyCalc does that - coordinates from a point and bearing/azimuth and distance -- plus. I don't know enough about it to attest for the accuracy but for RM/Station distances it's probably good enough. I use it a lot, it's a great tool. Guess I'll plug Holoscenes Wiki since that's how I first found it.

 

I like 2OldFarts solution (did yuse guys help at Giza?)- with the ends of the tape anchored and using a stick to keep the tape taught while inscribing a line all the way around the two RMs - what do you get??

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We're trying to plan out a return trip Wednesday or Thursday evening. I went by Lowes and bought a 48" pipe probe rod to aid in our hunt.

 

There is another member of our group who has a better metal detector. We may see if he can join up and help.

 

We will be using all the applicable techniques that everyone has shared here. I feel confident with all that I have learned of late from this thread.

 

We plan to retake all measurements from each reference mark to the station..... and between the reference marks themselves (if that would help).

 

If we are successful in the recovery, I think everyone here should log it.......especially since everyone has helped so much. :D

Edited by LSUFan

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Well, we're still getting rained on down here. Maybe we can try for this one next week, as we have a geocaching event this weekend.

 

I have found another thing to help in the search(es). Harbor Freight carries a 100meter tape reel that has metric on one side and SAE on the other for $15.

 

Our group has several of these now, which should make measuring easier, without having to do any conversions.

 

http://www.harborfreight.com/cpi/ctaf/disp...temnumber=36819

 

I'll let everyone know if we find the station..............or if that fails, see if I can get a deal on some airfare to fly everyone here in to show us how it's done. :o

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LSU:

 

I've got one of those from Harbor Freight also. It seems a bit stretchy, so don't go too tight on it. Otherwise, pretty good piece of gear for the price.

 

Good luck!

 

-- Klemmer

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We plan to retake all measurements from each reference mark to the station..... and between the reference marks themselves (if that would help).

 

If you find the station, it's probably unnecessary. However, Difficult Run is correct. Having both angles and the distance to one RM, if you could not find the station but do find both RMs, measure accurately the distance between the RMs. With this measurement, the distance from the other RM to the station could be calculated, allowing a more exact pinpointing of the station location.

 

EDIT: Just put this down on paper and realized it wouldn't be quite as easy as I had thought. I think the exact distance could be calculated, but it'll require more thought than I'm willing to give it right at the moment. :o

Edited by andylphoto

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We plan to retake all measurements from each reference mark to the station..... and between the reference marks themselves (if that would help).

 

If you find the station, it's probably unnecessary. However, Difficult Run is correct. Having both angles and the distance to one RM, if you could not find the station but do find both RMs, measure accurately the distance between the RMs. With this measurement, the distance from the other RM to the station could be calculated, allowing a more exact pinpointing of the station location.

 

EDIT: Just put this down on paper and realized it wouldn't be quite as easy as I had thought. I think the exact distance could be calculated, but it'll require more thought than I'm willing to give it right at the moment. :o

Yes, this is straight forward.

 

Google "law of cosines" and "law of sines".

 

These allows a complete solution of a triangle given one angle and 2 sides. Law of cosines is probably the one to use for this case.

Edited by Papa-Bear-NYC

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I really dislike the law of cosines, because although it is correct it is a lot of calculation and keeping track of which thing is which.

 

I find it much easier to add a line inside the triangle cutting it into two right triangles with one of them having an already known side and angle besides the new 90 degree angle. Then I work through these triangles one angle or side at a time using only one multiply or divide with a cos, sin, or tan at each step.

Edited by Bill93

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Yup...that would be it Papa Bear. I knew it had to be mathematically possible, but I am with Bill93. When I use trig, I like dealing with right angles, and do the same thing he does. If I learned this in high school trig, I mis-filed it long ago, and have never had to use it since. :anicute:

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Actually Guys, the Law of Cosines won't work for the example cited. The data you have can be formatted as Angle, Side, Side (or Side, Side Angle). The Law of Cosines only works on the Side, Angle, Side format. There are actually two solutions possible given SSA (or a**), as can be seen here.

In some cases, you will be able to determine just by sight which of the solutions is the appropriate one, but there will also be instances where the two solutions are so close to each other that you won't know which to use - I guess you could always try both!

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Actually Guys, the Law of Cosines won't work for the example cited. The data you have can be formatted as Angle, Side, Side (or Side, Side Angle). The Law of Cosines only works on the Side, Angle, Side format. There are actually two solutions possible given SSA (or a**), as can be seen here.

In some cases, you will be able to determine just by sight which of the solutions is the appropriate one, but there will also be instances where the two solutions are so close to each other that you won't know which to use - I guess you could always try both!

Actually, I would say yes and no.

 

Yes, the law of cosines gives a direct unambiguous solution for the third side when it's opposite the known angle.

 

No, it's not the case the " the Law of Cosines won't work for the example cited".

 

In fact you can solve the law of cosines formula for the missing side and you will get a quadratic equation, which when evaluated will give the two solution illustrated by your link. I'm not sure folks want the gory details, but here they are anyway:

 

The law if cosines states:
1) z**2 = x**2 + y**2 - 2 x y cos(alpha)

where x, y and z are the three sides and alpha is the angle between sides x and y

If you want side z (the one opposite the angle) it's easy, just take the square root of the right hand side. 

But if you want side x or side y (one of the sides adjacent to the angle) as in the present case, you just 
manipulate the Law of Cosines formula thus (assuming you want side x):

2) x**2 - 2 x y cos(alpha) + y**2 - z**2 = 0

Which is a quadratic equation.  


The standard form of the quadratic equation is

a x**2 + b x + c = 0 

This has 2 solutions:

x = (-b + sqrt(b**2 - 4 a c))/2 a
and
x = (-b - sqrt(b**2 - 4 a c))/2 a


For our Law of Cosines equation, the quadratic coefficients are 
a = 1
b = - 2 y cos(alpha)
c = y**2 - z**2


And so plugging in our triangle's sides and angle, we have our 2 solutions

3a) x = (2 y cos(alpha) + sqrt(4 y**2  cos(alpha)**2 - 4(y**2 - z**2)))/2
and
3b) x = (2 y cos(alpha) - sqrt(4 y**2  cos(alpha)**2  - 4(y**2 - z**2)))/2

Although the results contain a lot of cosines and other factors and it looks complicated, if you just plug in the given sides and the cosine of the given angle, it's all just numbers.


(I'm sure there must be a typo in there somewhere, I already found a couple :anicute: . Feel free to check the work, that's what this forum is for.)

 

When you come down to it, all the Laws related to solving triangles, including the Pythagorean Theorem, are all just special cases of the same general relationships that all triangles have. So for example, you can prove the Law of Cosines from the Pythagorean Theorem and vice versa. The trick is to find the simplest formula for the particular case you are faced with. I think for this particular case, you are just stuck with the dual solutions and the (slightly) complicated formula. But hey! that's why we're paid the big bucks! ;)

Edited by Papa-Bear-NYC

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Think I got it figured out...

 

Since RM1 and RM2 are set 34 feet from the centerline of Philpot Road, I measured the angle of the road using the satellite image at MyTopo.com.

With this, I got a value of 31.5 degrees. From the datasheet, we know the angle of "A" (viewed from the station) to each RM is 77.9 deg.

 

Now we have two angles and one side. - Yippee!

 

Then I cheated and used an online triangle solver. Here's the result:

 

5f3mtt.jpg

 

Angle A = 77.9, Angle B = 31.5, Angle C = 70.6

Side A = 121' 2", Side B = 65' 6", Side C = 121' 9"

 

Check the distance from RM1 to RM2 first. If it agrees with my calculations, you're good to go!

~ Mitch ~

 

P.S. - Please note that the sketch is scaled, but not oriented perfectly north-south.

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I just ran those numbers through my formulas for the "modified" law of cosines and using

 

alpha = 79.9 deg = 1.3945 radians

y (adjacent side) = 115.8'

z (opposite side) = 121.2'

 

Solution 1: 61.44'

Solution 2: -20.83'

 

Obviously Solution 2 is out so we have 61.44' = 61' 5.3".

 

The biggest uncertainty is side z, the distance between the 2 RMs, since that was done in the field with a tape over presumably somewhat rough ground and was not to survey standards (no offence, LSUFan) A quick check indicated that for every .1 foot error in the measurement between the RMs, the missing side calculation will change by about .3 feet. The error is magnified since the affect of z in the formula comes from the term (y**2 - z**2), the difference in the square of the length of the 2 sides. The squaring will effectively magnify the error.

 

This is in the ball park of Difficult Run's solution which depends on the accuracy of the aerial photo.

 

So we are definitely within spitting distance, but not quite ready to start digging.

 

I would feel a bit more sure of my number if 1) someone could check my math and 2) if LSUFan could really measure the distance between the RMs with super care. That means make sure the two ends of the tape are at the same level and that the tape is stretched as tight as you can make it. If you are running the tape up or down a slope, you need to correct for that.

Edited by Papa-Bear-NYC

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I goofed when typing up my results. - My bad.

 

The length of the sides should be:

Side A = 121 feet, 2 inches

Side B = 64 feet, 6 inches

Side C = 115 feet 9 inches

 

As PapaBear said, this all depends on the accuracy of measuring the angle of Philpot road using satellite imagery.

~ Mitch ~

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Here's my attempt at running some of the numbers given above...

 

6572abfc-c3a3-472e-b8f6-bc254389977b.jpg

 

Better check my math!!!

YES!

 

You uncovered one math error of mine (a typo): I used an angle of 79.9. Correct angle is 77.9.

Now my result for side b (which I call side x) is 67.53 feet, in close agreement with your number under the "Richard" heading.

 

This shows the result is not only sensitive to errors in the measured length on the opposite site (given as 121.2) but is also sensitive to errors (in this case a typo) in the angle.

 

Time to dig!

Edited by Papa-Bear-NYC

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Humm.....

 

I'm getting something a little different. Working from a couple of different aerial photos, after taking convergence angle into account, I find the azimuth of the road immediately adjacent to the area of interest to be right at 149 degrees. So, I first project RM1 from Anderson using 64.53 feet at an azimuth of 37:59:00 from the datasheet. I next project a line from RM1 at an azimuth paralleling the road of 148:58:48 (overkill on the precision, I know). Then I project a line from Anderson at an azimuth from the datasheet of 115:53:00. Where the two lines intersect should be RM2 assuming both RM's were really the same distance offset from the center of the road and that 148:58:48 is the azimuth of the road adjacent to the area of interest. This results in a distance between the RM's of a little more than 115.5 feet and a distance between Anderson and RM2 of a little more than 110 feet.

 

lsufan.jpg

Edited by tosborn

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So, I guess what this exercise has demonstrated is that a mathematical determination of the distance from RM2 to Anderson is not practical without some better data. Specifically, the distance between RM's, measured with care using proper techniques and equipment. Lacking that, your best bet, LSU Fan, is to correct a compass (that reads to the nearest degree) for magnetic declination, then measure the 64.53 feet from RM1 at a corrected azimuth of 218 degrees. You can sight to the same point from RM2 to see if you get a corrected azimuth of 296 degrees, as a check. This should get you close enough for probing/digging.

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We're still waiting for the rain to quit, so we can try and find this triangulation station. I am chomping at the bit now.

 

We are supposed to get 3-6 inches more of the wet stuff today and tomorrow. We're about to have a levee breach on the river 20 miles south of me. :blink: We are already a few feet above flood stage....and rising.

 

I don't think it will take much more rain, and that disk may float to the surface.....or sink a lot further than 18 inches. LOL :blink:

Edited by LSUFan

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To hell with the rain. Part the gosh dang waters and give us the distance from RM1 to RM2.

That way we can argue over the exact distances and angles! :blink:

 

~ Mitch ~

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To hell with the rain. Part the gosh dang waters and give us the distance from RM1 to RM2.

That way we can argue over the exact distances and angles! :blink:

 

~ Mitch ~

 

LOL. I might can oblige you there. If we are not getting hammered (with rain I mean) after work, I'll drive over there and tape it out. We had left the 2 reference marks uncovered........but they are right beside the road ditch, which may be slap-dab full.

 

So far today, the rain has been staying west of us.

Edited by LSUFan

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Get GPS Trackmaker and you can do all that figuring with it and then when done send it to GPS.

I have found many of them this way and will be the only way I do it.

 

I also find the azimuths with it.

 

If you use the box score you can add that in as points and the add the azimuth angle and distance.

 

It takes a little time to learn the tool but it is awesome once mastered.

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Ok, we ran back by ANDERSON yesterday evening. We took measurements the best we could, trying to keep everything level. I took the measurements using the metric side of the tape, and now see where I should have used the foot side, because that is how everyone has it figured.

 

We did find the station, at 24 inches below the surface. With all the flooding we have had, the water table was at 22 inches below the surface here. The hole would fill up with muddy water before we could dip it out enough to take a good pic. We tried stuffing rags, and even one of our shirts to stop the infiltration long enough to snap a pic, but wasn't successful enough. I posted a pic where you can see part of the disk but not enough to read it. You can make out the triangle on it. Oh, we were so close. :D We'll be going back when the water table drops, which may be next year.

 

The approximate measurements I got, are as follows

 

From ANDERSON to RM2 : 32.59 meters

 

From RM1 to RM2 : 34.35 meters

 

I didn't take a compass with me, as I wasn't really even going to look for ANDERSON but we probed and found it, and everybody here knows we were going to dig it up then. :rolleyes:

It really didn't line up with the arrow from RM1 just by sighting it. The distance was dead on, but it just seemed the direction wasn't. We swang a good arc with the tape measure and it was found a little further to the left side of the arc than I thought it should be. I'm not going to say that the box score info was incorrect, but will go back and see if the bearings are correct, now that I know where the station is. RM2 did line up good, just by sighting it. Maybe the numbers above will disprove my observations.

 

Anyhow, I posted some pics on the gc webpage, that may help. It was very overcast at that time, but not raining.

 

http://www.geocaching.com/mark/details.aspx?PID=CQ2753

Edited by LSUFan

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Nicely done LSUfan!

 

When you go back again, be sure to add as many measurements as possible including the distances from the RMs to the centerline of the road. It's possible that one of the reference marks was disturbed by road widening or mowing. On any recovery, I'll give the mark a "kick" to make sure it hasn't been broken off below grade.

 

Sure enjoyed the fun of watching your recovery efforts from afar.

~ Mitch ~

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Nice work, LSUfan!

 

From experience, I can tell you the arrows on the RM's are not accurate at all. I have seen a couple in solid mounting (undisturbed) that were easily 20 degrees off the mark. On the other hand, the azimuth numbers in the box score (if any) are quite exact (within survey grade tolerances). More exact than you will be with a handheld compass.

 

Keep up the good work. Send some of that rain back this way (SoCal). We could really use it! Our water table is non-existent!

 

--Klemmer

Edited by Klemmer & TeddyBearMama

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LSUFAN:

 

Did you look for the Azimuth mark?

 

OK, I see by your report you didn't. The next time you are out there, check near 32.40014N, 92.16405W to see if you can find it.

 

Thanks for reporting back to us.

Edited by tosborn

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Excellent work!

Too bad about the water table, but now you definitely know where it is. :)

Personally, I would log it found with what you have. I don't think anyone here would question your ethics. :)

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If you know any sea kayakers you should be able to borrow a hand bilge pump that would move enough water to get a clear picture. Don't need it to prove your find to me. kayakbird

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