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pgrig

Need Surveyor Help, Please!

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If you would, take a look at the 1946-era plot plan I found on the Web for the WW II fire control tower behind which was located MY0235.

 

As my log indicates, I believe this plot plan is the best evidence as to the location of the station, which was its point of beginning and the key point for the establishment of the marks for the fire control tower itself, MY4964.

 

My question is, can I expect that the barracks building in the center of the plan is correctly located on it (within say a foot or two)? In trying to measure distances from the SW and SE corners of this building to the station, I was using as a scale the 20-ft. width of the drainage easement coming into the site from the SW. Is this likely to be OK?

 

I'm heading back out there soon to re-measure and re-consider the site, and hopefully to dig for the station. Any comments anyone would care to make on my assessment thus far would be greatly appreciated! :D

 

It's a beautiful place!

 

Thanks,

-Paul

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You can hope for that, but since the diagram appears to have been created for diminsioning the easements, and shows no ties to the buildings, there is no guarantee that their location is anything but schematic. You have to try anything you can though. It is true that it would not be uncommon for someone to grab an existing plan and reuse it for the current purpose. Can't it be related to the tower as a check?

 

On the other hand the exterior appears to have been fenced, and maybe there is some evidence of that which can be recovered. Particularly at the SE'ly corner. And that exterior is tied by bearing and distance directly to the station #136, although the basis of bearing is not specifically shown.

 

- jlw

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Thank you!

 

I don't believe any of the 1945 fence still remains, but I didn't think of looking for remains of old fence posts...I'll try it. And BDT, I will try a measurement from RM1. It runs through the corner of the SE addition to the barracks, but I can try to estimate it.

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Thank you!

 

I don't believe any of the 1945 fence still remains, but I didn't think of looking for remains of old fence posts...I'll try it. And BDT, I will try a measurement from RM1. It runs through the corner of the SE addition to the barracks, but I can try to estimate it.

 

This is a prime situation where projecting a waypoint with your GPS would be most expedient!

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AZcachemeister--

I'm sorry, but I haven't ever done this yet. Would projecting a waypoint (which I don't understand) get me around the problem of 15 ft. or so of the 98 ft. distance between the RM and the station being underneath an addition to the barracks building?

 

[When I was out there the first time, I had assumed (there's that word again!) that the station was located underneath the addition, so I never even tried "centering" my GPSr on the station coordinates toward the parking lot. Another lesson learned the hard way.] :rolleyes:

 

Thanks,

-Paul

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and jwahl, I think you mean the SW'ly corner (?) . RM2 I plotted to be just inside this corner (the Description says 6.8 ft. N), but today this area is beyond a heavily overgrown chain link fence enclosure for what used to be a wind turbine--brish is 10 ft. tall and very thick. But I will continue to look for evidence of the old fence line.

 

-Thanks!

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Paul

 

Maybe this will help - I plotted the objects from the box score, then added the dimensions from the survey plat, (which appears to be based on either grid or true north - the difference being about 3/4 of a degree). I then overlaid that information with the image of the survey plat, and also with a Google Maps image from ScaredyCat's BM Viewer. Here are the results:

 

752f8dec-88fa-4fe3-8666-c9e158f5d6f0.jpg

 

9d74a842-5006-486c-993f-c8bd735aa4f7.jpg

 

I scaled a distance of 39' to the former SW corner of the barracks building, and 48' to the SE corner. I wouldn't guarantee an accuracy better than about 2-3 feet, however, based on the overall fit. With a survey instrument, you could occupy a random point where you could see both MY4964 (the center of the tower should suffice), and RM 1. Then perform a resection to obtain occupied coordinates from which you can stake out the location of MY0235. This method (depending on how well you can determine the center of the tower) should get you within a few inches of the actual station, narrowing the size of the hole for digging. Of course, not everyone has access to the necessary survey equipment, but if the folks at Halibut State Park are really interested in unearthing this mark, I might be able to help.

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Holtie22--

 

Wow!

 

OK, leaving aside that I have no idea how you overlayed these images, could you tell me what you mean by this and how you get there?

 

"I scaled a distance of 39' to the former SW corner of the barracks building,

and 48' to the SE corner."

 

Because I was thinking of digging about 44 ft. from the SE corner of the barracks, on a line bearing 240d, and about 40 ft. due (S) of the SW corner, following what I saw on the 1946 plat. [This assumes that I try to measure the distance and direction from RM1 much more carefully, and put on a major hunt for RM2 (which I'm afraid isn't intervisible with the station anyway!). It also seems to me that if I could find the NW or SW corners of the old fenced enclosure, I'd be in better shape, and I will search for fence posts (without much hope).

 

As far as the park's interest, another fascinating story connected with this site. The Asst. Supt. told me that the state has now started receiving letters from someone with a residual interest in the old Rockport Granite Co. (which dug the quarry and went out of business in 1929) telling the state to cease and desist from trespassing on their land (by occupying a State Park on it since 1981!). They have sent surveying parties around, and the state has threatened them with arrest for trespass if they try it again. :ph34r: So the Asst. Supt. is also on regular "surveyor patrol". I believe that two ears or a tail from a surveyor earn him $25.00.

 

He was very kind, however, and is certainly interested in our marks (he took me right to RM1 and over to another apparently missing mark located about 1000 ft. westerly from the barracks building). And I can ask when I stop back by how they would feel about some on-site work by someone who isn't an amateur :rolleyes:!

 

For what it's worth, I believe that the mark for MY4964 was likely located to the NNW of the center of the tower, perhaps 3 to 5 ft.??, since that's where the illustration shows that the depression rangefinder was located, on its "block" base, the center of which was the station location.

 

But I suspect that dig I must :) . If this is the case, from your great stock of knowledge, where would you invest your elbow grease (w/respect to the platted barracks bldg. corners)?

 

Again, wow! And thanks for all your effort!

-Paul

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Thank you!

 

I don't believe any of the 1945 fence still remains, but I didn't think of looking for remains of old fence posts...I'll try it. And BDT, I will try a measurement from RM1. It runs through the corner of the SE addition to the barracks, but I can try to estimate it.

 

This is a prime situation where projecting a waypoint with your GPS would be most expedient!

Since this is a location adjusted station, projecting a waypoint with a GPSr would be less accurate than just looking for the station directly with the GPSr.

 

pgrig- I didn't see that the RM was opposite the addition. Still, if you have a precise enough compass (mine will read to ½ degree, but in practice the accuracy of reading more like +/- 2 degrees or something), you could actually survey around the building to the mark with perhaps more accuracy than your GPSr would afford in looking for it directly. You'd have to do some trig analysis to see what your error-radius would be like over the distances of the 2 or 3 shots you'd have to take around the building, and assume a +/- 2 degree compass reading standard deviation. Umm the standard deviation increases as the square root of the number of shots taken and..... heh, well it would be fun to work on. The point of that is to not plan to take too long of survey legs, more shorter ones would probably afford better accuracy. As I recall, with a 2 degree accuracy range, 30 foot legs are sort of optimum.

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Since this is a location adjusted station, projecting a waypoint with a GPSr would be less accurate than just looking for the station directly with the GPSr.

 

 

Perhaps.

Or maybe a projection from a known correct location could compensate for the GPS inaccuracy happening that day.

 

Either way, it appears a metal detector will be in order as mentioned earlier.

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AZcachemeister--Thanks!

 

Sadly, when last heard from, the station was a foot underground. I don't think my detector will go that far, but I will certainly try.

 

BDT--

 

Is this my big break (into the world of surveying)? Does this mean I need a hard hat and a large wooden table on a platform?

 

When I shot the back azimuth from RM1 with my compass (in practice, I seem to be able to read w/in 2-3d on it), it sure looked like it paassed through the addition, but Holtie22's marvelous image makes it look like it's a very close call. First order of business will be to go back and run a tape, sight over it, and see what I find.

I was so fascinated with the site the first time around that I ran out of time...

 

-Paul

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c86d4dd6-3da1-4884-b218-769cd1fee6a6.jpg

 

I have added to the survey plat image a hypothetical building footprint from the Google image. If my assumed dimensions are correct, then my best estimate of the station location would be 22' SE of the SW corner of the addition, and 18.5' SW of the SE corner. Those numbers would change to 19.5' and 17.5', respectively, if I shift the footprint to match the tie distances to the station and RM 2 given in the 1953 recovery report. So you can see there's a lot of uncertainty with this method.

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c86d4dd6-3da1-4884-b218-769cd1fee6a6.jpg

Holtie,

 

I like your overlaid images.

 

I don’t want to derail Paul’s question, but if it is quick to explain, could you tell me which program you used to create your red and blue lines and which program you used to combine them with the other images?

 

I can create azimuth/angle lines in AutoCAD LT but I can’t figure out how to use Photoshop Elements to overlay precision drawn lines from AutoCAD LT. I was just curious how you created your images.

 

Good luck Paul. Holtie sure has put some work into this.

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If I can contact my friendly Asst. Supt. and get permission to bring my car in, I will go back up there later this week and see how hard it is to dig in the driveway/parking lot (a good thing to find out before taking too much more time from all of you :) ). And who knows, I just might get lucky with my detector that day...

 

Holtie22, how did you come up with your distance of 48 ft. to the SE corner of the (unmodified) barracks building? That seems quite long to me, and I had something more like 44 ft. in mind...

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Sadly, when last heard from, the station was a foot underground. I don't think my detector will go that far, but I will certainly try.

 

 

Under the circumstances, I would consider it's reported depth to be good news.

It will certainly be more difficult to recover, but the chances of it actually being there are also tremendously better.

If I were you, I'd do a little practice run somewhere using a simulated BM disk, maybe an old brass belt-buckle? (or a real disk if you have one...) At one foot depth, the signal will probably be weak, so operator skill could become the most important factor.

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TillaMurphs -

 

I use AutoDesk Land Development Desktop, which has AutoCAD Map built into it, allowing me to manipulate images within AutoCAD.

 

Paul -

 

Once the image is in AutoCAD, properly oriented and scaled, it is a simple matter to measure between any two points. The difference between your measurement and mine is probably related to scale factor. There may also be distortions in the image due to how it was digitized. Was the original scanned or photographed?

 

If you examine the last overlay, you will notice that the blue lines do not lay exactly over their counterparts on the survey plat, yet the blue lines were input using the dimensions given, so they should be more accurate than the image. I attempted to scale and orient the survey plat based on these lines.

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Holtie22--

 

All I can say is "I wish I could skate like that!" :)

 

The plat was grabbed via SnagIt from a scanned image that was part of a larger image I found on the web and then saved as a .JPG. Since you've already invested about a week's worth of your time on this, here is the document I copied.

 

I was interested to see that the "blue line" (the fence line) on your composite almost exactly overlies the northerly park boundary as shown on the Scaredy Cat map.

 

Could you read off your plan the distance that RM2 lies to the SW from the SW corner of the bright square in your composite? I believe this square is the (now unused) 1990s concrete pad that was the base for the old wind turbine, and I could measure this distance on the ground.

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The plat was grabbed via SnagIt from a scanned image that was part of a larger image I found on the web and then saved as a .JPG. Since you've already invested about a week's worth of your time on this, here is the document I copied.

 

I was interested to see that the "blue line" (the fence line) on your composite almost exactly overlies the northerly park boundary as shown on the Scaredy Cat map.

 

Could you read off your plan the distance that RM2 lies to the SW from the SW corner of the bright square in your composite? I believe this square is the (now unused) 1990s concrete pad that was the base for the old wind turbine, and I could measure this distance on the ground.

 

Paul-

 

I went to the source you gave and got a better quality image of the survey plat.

 

ea36f5d7-3bdb-49be-97bd-ae1f109e24ca.jpg

 

It still doesn't line up exactly with the blue lines, and it depicts the building about 2.5' NE of where the 1953 tie measurements would put it. You should note that the fence line is depicted on the plat as lying a foot or so inside the tract boundaries. (See double blue line). This is confirmed in the 1953 recovery report, where the distance from RM 1 to the fence is given as 19.6'. In the same report, however, the SW fence corner is described as being 84.2' from the station and 6.8' from RM 2. This puts the fence corner right on the tract boundary rather than a foot inside it. We may be dealing with sloppy measurements from 1953.

 

Scaling the distance from RM 2 to the corner of the bright square, I get 17.5'. The uncertainties associated with this image may be even greater than what we have seen on the survey plat, again about 2-3 feet.

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Holtie22--

 

OK, it's official. You've now invested enough time in this one to qualify for our Surveyor of the Month

award! And your prize? An hour of uninterrupted digging time (shovel provided) at the most interesting site I've seen in my short career. I hope to be able to get up there tomorrow and bring back more news. Whether this includes an actual dig, I'll have to wait and see. I will also inquire about how eager they would be to have me do a better targeted dig. :laughing:

 

As I was reading Shorelander's account of the classified SECRET BMs in Hawaii, I was thinking about these fire control towers around here. As far as I know, every one of them had a published BM under its rangefinder, and one or more nearby marks from which the location of these tower stations was derived.

 

I wonder if anyone can tell us if these were "cloaked" during WW II. It also makes me wonder about the several Nike sites around here, again each with its own BM.

 

Thanks again!

-Paul

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pgrig -

 

I recommend establishing a temporary survey point X west of the line between MY0235 and its RM1.

Measure the bearing from RM1 to X. (Be sure to it is True, not magnetic.)

The difference (turning angle) between this bearing and the datasheet's bearing from MY0235 to RM1 can be called a.

The distance between RM1 and MY0235 is known from the datasheet. Call it B.

Measure the distance from RM1 to X and call this distance C.

 

So, now you have a triangle made of points MY0235, RM1, and X. Two lengths of two sides (B and C) are known, along with the angle between them (a).

 

Next calculate 2 items:

The angle at point X between looking from X to RM1 and looking from X to MY0235. Call this angle b.

The distance from point X to MY0235. Call this distance A.

 

From a math formula book:

A = sqrt [ (B^2 + C^2 -2BC*cosine(a) ]

sine(b/2)= sqrt [ (p-C)*(p-A)/(A*C) ] where p= (A+B+C)/2

so take the inverse sine of the square root above and multiply by 2 to get b.

 

The alternative for getting b is:

cos(b/2) = sqrt [ p*(p-B )/(A*C) ]

 

So, to get to the station from RM1, you will need to measure 2 bearings (RM1 to X, and X to MY0235) and 2 distances (RM1 to X, and X to MY0235).

 

You will probably need to bring a 2 or 3 stakes for the sightings.

 

Edit to take out smiley replacement of part of a formula. :laughing:

Edited by Black Dog Trackers

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Thank you, BDT!

 

I can do this! :laughing:

 

Now, of course, as a surveyor, I will need to be paid a good deal more money for these

recoveries...and things with a square root sign in them even have an additional charge!

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Another time-out error! [Don't hit "Post" after you see this. It apparently does NOT mean your post failed.]

Edited by pgrig

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OK! :laughing:

 

I'll assign that task to our subsidiary, Discount Benchmark Surveys, Inc. DBSI are the guys who give 20% off the usual (astronomical) surveyors' rates for work that guarantees only +/- 2.5d accuracy... They were heavily involved in the site work for Boston's Big Dig, and won nationwide notice for their performance.

 

It will be very interesting to see what I come up with. Wish me luck!

 

I'm off to find something I can use for a couple of "leave-behind" markers (since I don't think I can do all this in one visit; my hands will be trembling too badly). Now I see what surveyors use all those cool little widgets for....

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One quick thing to use is a 60p nail or a thing called a barn spike which is similar. Both are like long nails about 6" long and make good temporaty points and can be driven into the ground with a hammer or hatchet if it is not really concrete hard.

 

There are a dozen ways to construct a search area from RM1. For example you could set a site pole on RM1 and go over the the vicinity of your station and line up a point right on the extension of the line from the RM to the edge of the building. Now you can measure that line the given distance for the RM1 to station. Then take a careful compass bearing from RM1 to that line which will be coincident with the corner of the building (addition).

 

Now you have your bearing, and can subtract what it is supposed to be to the station per the box score and get an angular difference. Say it is 3.5 degrees. Many simple scientific calculators contain trig functions, so you can now take the sine or tangent of that angle and multiply by the distance and that will give you an offset to go estimating perpendicular to your line. For 3.5 degrees and distance to RM of 98.48 ft, that would give you 6.01 feet offset. That is not perfect because you measured out the full distance on your trial line , but if the angle is small it will not make much difference and the angle or your estimate of perpendicular is not going to be that precise anyway.

 

If necessary it can be precisely computed the small distance back towards RM1 set off. But I think it would get you within a foot depending mostly on the accuracy of your compass bearing with respect to the plot basis of bearing.

 

- jlw

 

PS if you believe that the main part of the building is as reported in the 1953 recovery note you can also measure off 36.7 feet from there and correlate the distances.

Edited by jwahl

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... AutoDesk Land Development Desktop ...
For those of us who may not have access to professional grade (and priced) software, has anyone used free/open source/inexpensive programs that might be capable of this sort of thing?

 

-ArtMan-

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... AutoDesk Land Development Desktop ...
For those of us who may not have access to professional grade (and priced) software, has anyone used free/open source/inexpensive programs that might be capable of this sort of thing?

I use Manifold (price about $250 US) for most of the maps and georeferenced images I use or create. That's about the upper limit I'm willing to pay for "hobby" software, but Manifold is a really top-notch product, IMHO. It is actually professional grade itself.

 

For the occasional CAD drawing, I've used TurboCAD Deluxe ($130 US). Unfortunately, it doesn't really integrate with Manifold, and the version I have doesn't work with georeferenced data.

 

There are definitely open source versions of GIS out there, and there are probably open source CAD, too. The problem with open source programs is that they tend to be quirky, and generally do a couple of things really well, and most other things poorly or not at all. You have to hunt for one that does exactly what you need to do, and hope that there is documentation somewhere.

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There are free programs out there that can do all this.

 

I have mentioned them many a time.

But am still the only non pro using it.

That's fine with me though.

 

There are also little tricks to overlaying images in Google or many programs by creating a transparency and then placing and adjusting(calibrating) the imagery or overlay.

You can also create your own maps with this data and send it to your Garmin Units and many others.

 

But to explain all of it would take a while and if you just go and play with GPSTrackmaker for a while you will see yourself.

 

But As in the past no one has heard me.

It is awesome and can be an only tool once learned.

 

Back to logging my finds for this month.

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There are free programs out there that can do all this.

 

I have mentioned them many a time.

But am still the only non pro using it.

That's fine with me though.

 

There are also little tricks to overlaying images in Google or many programs by creating a transparency and then placing and adjusting(calibrating) the imagery or overlay.

You can also create your own maps with this data and send it to your Garmin Units and many others.

 

But to explain all of it would take a while and if you just go and play with GPSTrackmaker for a while you will see yourself.

 

But As in the past no one has heard me.

It is awesome and can be an only tool once learned.

 

Back to logging my finds for this month.

 

I heard ya!

I haven't used it much yet....

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You will like it once you figure it out.

There is another one called DGTV.

David Gills Terrain Viewer but it is not real user friendly and you have to process a lot of stuff but it is fun to play with.

It is imagery from the Space Shuttle Radar Topography Mission.

It is awesome as well for Terrain data.

I thinks dem are called DEM's.

Digital Elevation Models.

 

I will say though that we are using more accurate equiptment to find less accurate marks.

My Opinion Only.

 

So our precise defines are really alot of work and may contain inherent erros in all aspects.

The FIELD WORK is where you really show your stuff by locating the marks by whatever means it may take.

 

I wish it was a lot easier for me to add all the details for each station and the progress and final report of recovery with updated coordinates.

But then that is getting into alot of work for a mere volunteer like me.

 

So I just keep that data and add to the ever growing list.

 

If I had more time and money I would have some awesome reports but alas I am a mere disabled volunteer doing the best I can with what I can afford.

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Update:

 

Thanks to all the great advice and assistance I got (with special thanks to Holtie22, BDT, and jwahl) I managed to calculate a point for MY0235 (see photo).

 

MY0235-Resected.jpg

 

It seemed to work correctly and give me a position for the station roughly in the right spot. Also, the point I calculated seemed to lie on the same azimuth as the station in the tower (MY4964), within 1d to 1.5d. I was sighting on a point a bit to the (W) of the center of the tower, where I estimated the rangefinder was located during WW II.

 

Unfortunately, the driveway/parking lot is very hard-packed gravel, sand, and rocks. I dug down about 6 in. at the indicated point before postponing operations. ;) [The 1953 report said it was down 1 ft. and set in granite ledge .] Today I went out and procured yet another tool--a foot-long prybar with a tapered pry at one end and a rt. angle pry-hook at the other I can use to pound on and drive through that nasty stuff.

 

The Asst. Supt. was not in, so I couldn't chat with him.

 

BDT, I probably screwed up, but was unable to use your "alternative" formula. Instead I used what I had as the Law of Cosines: cosA = (b^2 + c^2 - a^2)/2bc. My angle came out to be 121d, with the distance from my point to RM1 at 73.75 ft. and from my point to the station at 37.54 ft.

 

I had fun!

 

-Paul

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The location shown in your photo looks like about 6 feet or less from the curb stones, and if we were to believe in the positions shown in the plots earlier in this thread, it sure seems like it should be further SW by maybe 5 or so feet.

 

How well did you position fit the ties to the original structure.

 

Aerial photos are not perfect by any degree, but it makes me wonder.

 

- jlw

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Hi Holtie22--

 

I spent about an hour bushwacking around for RM2. Although the area is covered in thick brush and thorns, I lopped away a lot of it and even searched in any bit of ledge I could see that could possibly be near the estimated azimuth of the mark. The bright square is enclosed with a 10 ft. high cyclone fence and is a few feet higher than the station or RM2, making them not intervisible and hard to tape. It was 40 ft. from my estimated point for the station to the (brighter) granite blocks around the NE side of the enclosure, but I did not try taping segments on the other (SW) side. I searched from 10 to 20 ft. back from the SW corner of the enclosure.

 

jwahl--

 

You're right... The one tie to the barracks that I checked was the distance to the SE corner. I got 46.93 ft., as against 37.5 ft. in the 1943 entry and 48 ft. in Holtie22's reported scaling. I had already been expecting a distance more like 44 ft., since I had considered the 1943 entry not to be realistic. Sigh... My station position was 5.1 ft. from (perpendicular to) the granite border blocks SW of the SW addition, and 12.4 ft. from the addition wall. I found the addition to measure 18.3 ft. wide (on its southerly side) and 22.1 ft. deep, though, and on the drawings it looks the other way around. Sigh again... Perhaps I will need a backhoe instead of a shovel? :)

 

[There seem to be a number of problems with the earlier descriptions. For example, in 1953, the station was described as being 36.7 ft. SW of the SW corner of the barracks. This is not credible. In 1943, it was said to be 27.5 ft. SE of the same SW corner, and this seems much too short.]

 

I'm betting that the barracks was only (mis)placed schematically in the plot plan.

 

I am heartened by finding my station point so close to the azimuth line to the tower station, MY4964.

 

____________________

 

Now I'm going to take the weekend off. My daughter is coming to visit from CA, so I will be focused on her instead. ;)

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Progress Report:

 

The log for MY0235 has been updated with a note for my visit of yesterday, documenting the recovery of RM2 :huh: but my repeated failure to recover the station disk :anibad: . A fourth visit will be made to continue the assault on the parking lot, likely after a fourth resection to produce another station location estimate. I no longer believe that surveyors have an easy time of it.... B)

 

If anyone wants to go back and play with the photos/plans, I took the actual dimensons of the original barracks building. It's 45 ft. 1" long and 26 ft. 10 in. wide. However, if I try scaling it off of the 1946 plot plan, the barracks building measures 41 ft. long by 22 ft. wide. :ph34r:

 

-Paul

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Congratulations Paul!

 

Great progress indeed! Your persistence pays off once again. With 2 well-defined points to work from, this station is as good as found. Even digging through hard-pack becomes a whole lot easier when you are confident that you are digging in the right place. Send up a flare when you find it.

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Hi Again, jwahl--

 

The point I located from RM2 was about one foot (SSE) of the point I located from RM1. I tried another resection, but must have messed up the math. It may be time for a spreadsheet that solves triangles and a first time outing for my trusty laptop. :) I'm all thumbs on my straight calculator. Or maybe you'd like to donate a slightly used total station?

 

-Paul

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Hi Again, jwahl--

 

The point I located from RM2 was about one foot (SSE) of the point I located from RM1. I tried another resection, but must have messed up the math. It may be time for a spreadsheet that solves triangles and a first time outing for my trusty laptop. :) I'm all thumbs on my straight calculator. Or maybe you'd like to donate a slightly used total station?

 

-Paul

Hi Paul

 

I find that getting accurate azimuths is much harder than getting accurate distances, so if you use 2 tapes and simultaneously measure from each RM and hold the tapes where the two distances from the data sheet or your calculations cross, you will be right on it. Sometimes I stick a screw driver in the ground exactly 1 foot past the mark (or any distance easy to subtract out) to hold the end of each tape if you are alone.

 

If you have just one tape, start with the first RM and fix the end and then draw a small arc (with a screw driver in the dirt, or with a trail of white powder) at the end where the station is located. Then fix your tape at the other RM and see where the distance for that one crosses the arc from the first RM measurement. Where they cross, you got it.

 

Sometimes steep slopes, bushes or boulders (or the corner of a building) get in the way but I think your site will be OK in that regard. This way you can ignore the fine details of the azimuths. Works for me.

 

If the corner of a building is in the way, a little math at home will tell you how much to add to the distance to make up for the bend in the tape. (c**2 = a**2 + b**2 as my old Greek friend Pythagoras used to say). I did this correction for a station that was 4 feet below the RM with a 2 foot high ledge along the way. The corrected distance was within an inch of the found station (yes found: see PF1147)

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I find that getting accurate azimuths is much harder than getting accurate distances, so if you use 2 tapes and simultaneously measure from each RM and hold the tapes where the two distances from the data sheet or your calculations cross, you will be right on it.

 

This is excellent advice from the master!

Should work like a charm... :)

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Paul,

 

I read your latest log. I am impressed. You got the Massachusetts DCR to clear brush for you!

 

Next you will have the local department of transportation out there with a dump truck and a backhoe to help you excavate for the station mark.

 

Keep up the good work.

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Thanks to all of you!

 

Would that this were simply a windswept New England granite dome... :D Something easy, like nipping up Katahdin for a quick scramble through a misty pile of boulders.... :laughing:

 

For those of you who have not closely followed the saga of Capt. Paul and the hunt for the Great White Mark (think Gregory Peck in a pea coat peering off into the New England coastal fog), bear in mind that straight-forward simultaneous taping is not so easy here. The bearing from RM1 to the station (98 ft.) has a hunk of building in the way and the other (RM2, at 75 ft.) has about a 5-6 ft. "hump" with a chainlink fence around it cluttering up the line. (That having been said, it might indeed be a real good idea to try and "straighten out" the line from RM2 on my next visit. Problem is that I don't have a good way to hold both ends of my tape 5 odd ft. above ground.) I may need to innovate, adjust, and overcome (or hire a rodman; Shorelander, you could do this on your next mysterious swing through Boston...). Or maybe a couple of my full-sized traffic cones with long dowels inserted in their centers...hmmm.

 

But this is actually a real fun one, and it's still one of the most beautiful and historic sites I have worked on thus far (remember the historic fire control tower?). I get to practice (and screw up!) something that previously I never knew existed--"resection", or solving triangles for a missing side and angle, after you've measured (or been given) two of the sides and an angle. I have discovered what that "cos^-1" key on my calculator does :ph34r: and I even survived revisiting the quiet terror of my high school trig classes. I also educate tourists on the Coastal Artillery Service, the 16" guns of Battery Murphy in Nahant, and the function of the depression rangefinder (sigh...more trig).

 

Now about that front-end loader....(I have actually thought of asking the DCR to take a swipe at the parking lot with one of their little tractors. :) I think I already have it narrowed down to about a 4 ft square plot....) That is if they don't offer me a job as a Visiting Interpreter first and let me drive the tractor in my spare time...

 

-Paul

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Papa-Bear:

 

I went back and read your account on Mt. Pleasant. Again, wow!...

 

Questions:

 

1. How do you in fact secure the end of you tape while measuring? So far, I just put a handy rock on top of it, which is somewhat imprecise (if the tape slips under the rock, or there are no rocks handy atop the ledge I'm taping). Perhaps a mini tripod (there's one in my camera bag somewhere), weighted down somehow?

 

2. Is there a simple "triangle-solving" calculator, like for doing a resection?

 

3. Do you correct for long distance (75 ft. or so) tape sag (like going 3-4 ft. downhill) by solving rt. triangles over the "sag" distance?

 

4. How do you do all this by yourself? :)

 

-Paul

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Papa-Bear:

 

I went back and read your account on Mt. Pleasant. Again, wow!...

 

Questions:

 

1. How do you in fact secure the end of you tape while measuring? So far, I just put a handy rock on top of it, which is somewhat imprecise (if the tape slips under the rock, or there are no rocks handy atop the ledge I'm taping). Perhaps a mini tripod (there's one in my camera bag somewhere), weighted down somehow?

 

2. Is there a simple "triangle-solving" calculator, like for doing a resection?

 

3. Do you correct for long distance (75 ft. or so) tape sag (like going 3-4 ft. downhill) by solving rt. triangles over the "sag" distance?

 

4. How do you do all this by yourself? :)

 

-Paul

For this I was alone. On a previous trip to the site, I had a friend who held the tape. I did one tape at a time, since I had already narrowed the spot down to about 1 - 2 sq. feet on the first visit with 2 tapes and found the probable drill hole.

 

I put a very heavy rock on the end of the tape. In dirt, a solid screw driver would work. The Tape's end has a little right angle crick about a half inch long and the rock presses this into the bedrock. I pulled the tape very tight and it stayed fast.

 

The Tape was laying on the bedrock till it came over the little ridge. Then I just pulled the tape tight. I did not try to correct for the sag since the distance was not too long (about 30 feet). I did clear all the intervening brush first.

 

No canned formulas. I just broke it down into a couple or right triangles. The tape was the hypotenuse. The height of the ridge (2 feet) was the abscissa and the horizontal distance (the unknown) was the ordinate. There were 2 pieces to add together, the part before the bend in the tape (2 foot ridge) and the part after the bend, If you just have a slope distance - such as when the RM is x feet higher of lower than the station and you have a straight shot with the tape - you just need one triangle. Just stuck the numbers into an excel spreadsheet and dug out the correction. The amount of correction was about 4 - 6 inches as I recall, but it was reasuring to get very close after making the correction.

Edited by Papa-Bear-NYC

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Typically in the surveying textbooks, the ends of the tape are held level and sag is the droop in the middle. Slope distance (ends not level) is used only when necessary. If an end of the tape is above the point of interest, they use a plumb bob to get the end of the tape over the point. Works best with two people, so if you are alone you make do with what you have, as PB did.

 

I doubt a camera tripod high enough to clear a fence would stay upright with the tape at a reasonable tension. If you can see through the fence, sight the point where it intersects your line, mark it, and measure each way from the fence. If you can't see through, you might have to resort to a more complex set of triangles.

 

To get around the corner, assuming it is a right angle building corner, measure from each point to that corner and the perpendicular (shortest) distance to the building wall. Solve the triangles for the other sides. Call the building walls the X and Y directions. After solving the right triangles add up the X value to the wall from the first point and the triangle side in the X direction from the other point (calculated, too hard to measure accurately). Ditto Y. Find the hypotenuse of the bigger triangle with X and Y sides (projected through the building) and the distance between marks as the hypotenuse.

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No joy... :mad:

 

I went out yesterday and decided my best two estimates of location for the station were (1) a direct taping from RM2, passing the tape through the chain link fence that intervenes on the line and (2) a resection run from RM2. I am posting an image in a note to the station log. With the help park staff (who took pity on me and brought out a huge rock drill normally used for quarry demos :ph34r: and an iron bar), I dug down 2.5 ft and sank the drill bit another 8" further w/o hitting ledge. Sigh... I will now see if Holtie22 meant it when he said he might come down and actually set up to run a survey for the station...But for now, Moby Mark wins.

 

-Paul

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