holograph
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Posts posted by holograph
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What do you all make of this? I found AH7469 today, and just happened to see this posting, which is supposed to be the same mark! I know I didn't mix up my pictures, so I thought the poster on Waymarking.com may have. But, I cannot find his on the NGS database. Maybe I'll just go back to the park area and scour it for disks, to see if I can find it. Any ideas?
Maybe it is a replacement for EW1813?
Is there more than one cannon in that park? The disk that is logged on Waymarking is 0840 Q, but the disk at AH7469 is 0840 N. The K,L,M,N marks in this series are part of the NGS database, but Q is not. They all seem to be near each other at that park.
When I compare photos of the cannon, there is a chip off the corner of concrete base of the cannon pictured for 0840 N, but no chip off the corner of the concrete base the 0840 Q disk shown in Waymarking. Also the cannon shown in the Waymarking photo of 0840 Q seems to have a patch of green grass to the right of it, but the cannon shown for 0840 N seems to be surrounded by paving.
edit: oops, andylphoto beat me to the submit key. :-)
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The straight and curved lines on holograph's diagram are purely the result of the projections used.
Indeed. Here is a different map projection that is designed to show all great circle routes to or from Omaha as straight lines. Great circle routes through points other than Omaha would not necessarily be straight lines in this projection. The same two lines are shown on this projection -- the red is the great circle, the blue is the rhumb. However, unless you lay a straight edge against your monitor, your eyes could trick you into thinking either or neither of the lines is straight.
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Just for completeness, and because I wanted to see how much difference it makes, here is a map showing the difference between the great circle azimuths (as calculated by INVERSE) versus the rhumb line azimuth, otherwise known as the true course. I calculated the lines between Omaha, Nebraska and Denver, Colorado. These two cities are far enough apart that the difference between the great circle and rhumb lines are just perceptible.
For anyone else who has been following this thread, a rhumb line is the path that an airplane would follow if it navigated on a constant bearing, and is the path that most navigators choose for simplicity. If a pilot wanted to fly on a great circle, he would have to constantly adjust his bearing. The map below is projected in a Mercator projection, which was designed for navigation and it shows rhumb lines as straight lines. Although a great circle appears to be curved on this map projection, in reality it is the straightest and shortest distance between two points on the globe.
The red line is the great circle, and the blue line is the rhumb. It shows that difference in forward and back geodetic azimuths (i.e. great circle azimuths) is not 180°, but the difference in the forward and back rhumb line azimuths is exactly 180°.
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I'll post a map later when I have time, but here is a verbal explanation, if you understand the difference between a rhumb line (a line of constant bearing) versus a great circle route (i.e. the shortest route or line of sight). A rhumb line crosses each meridian at the same angle, so the back azimuth would be exactly 180 from the forward azimuth. A Mercator map is specifically designed to show rhumb lines as straight lines.
A great circle is not a rhumb line, because it does not cross each meridian at the same angle. Thus, the back azimuth and forward azimuths won't be 180 degrees apart, even on a perfect sphere. A great circle, or line of sight, on a Mercator map looks something like a sine curve.
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Just a piece of off-topic trivia I came across the other day. We've often discussed why azimuth marks are always about a mile or so from the station mark, and there have been a number of explanations: it needs to be far enough so that a precise measure can be made, and so on.
I was reading a book on surveying from about 1910, and the author stated a very simple and practical reason -- the azimuth mark should be about that far away so that the telescope doesn't have to be refocused to sight on it.
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The surveyors may have better answers, but one reason the azimuth and back azimuth are rarely the same is because the meridians converge, even on a perfect sphere. Or another way of looking at it is: if you plot a great circle on a Mercator map (or any other map that has parallel meridians), the line is not straight, and so the azimuth and back azimuths are not complements.
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Yeah, sure it is. Or was in 1997, when the Terraserver aerial photo was taken. Unfortunately, time marches on:
See the March 14, 2005 Eminence city council minutes:
Subject: Water Tower Removal Bid – Public Works Director William Smith reported that two bids were received for the old water tower removal. The lowest bid was for $10,600.00 from Iseler Demolition. The other bid was for $13,700.00. Jay Hoffman, who is working with him on the bidding and overseeing the project, has recommended we take the lowest bid. The work will probably be done sometime in April after the company completes a project they are working on in Richmond, KY. Discussion held on how we would pay for this project. City Clerk Doane suggested transferring money from a project item in the water and sewer reserve account, which will not be completed this year to the tank demolition expenditure. Motion made by Member Ferguson and seconded by Member Stephens to accept the lowest bid of $10,600.00 from Iseler Demolition for the water tower demolition and to authorize transferring $10,600.00 from the line item valve replacement project to water tower removal in the water and sewer reserve account budget. All members present voted “Yea”.
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Arrrgh.
Went to try out the given formula with a set of simply arranged data points, which I had arranged in a perfect square (for sake of simplicity).
The formula blows up before you can even get started, because computing K1 gives you 1/0 ...
You picked the worst possible arrangement, one that is guaranteed to be indeterminate. There is one rule that must be followed:
Draw a circle through your three control points. The unknown point cannot lie on that circle. If it does, the solution is indeterminate. Or restated in terms of the following diagram, if (x + y) = 180°, then there is no solution.
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I noticed that India's National Programme on Technology Enhanced Learning has posted 30 hours of video lectures on YouTube for a Civil Engineering Surveying course. You can see the playlist here.
If you are interested in the nuts and bolts of surveying, you may be interested. The instructors do, of course, have distinct Indian accents.
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Nice job as usual Holograph. It looks like recent March entries didn't make it in. Anyone know what the latest date made was? I did a few on the 29th but that will have to wait till next month I guess.
It looks like the 23rd or the 24th was the last report date. There were eight reports for the 23rd, and one for the 24th.
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The March statistics have been updated on the statistics page and on the list by county.
In addition, the maps have been updated.
It looks like shorbird has a new record for a station with the most time since its last recovery (171 years). Check out MZ1954 (datasheet). Although a number of cachers had logged it in GC.com, shorbird was the first to report it to the NGS.
Also, CallawayMT logged the lowest station with a visit to GS0206 (datasheet). Again, a couple of cachers had logged it in GC.com, but CallawayMT was the first to report it to the NGS as GEOCAC.
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The MEGS parties in 1932 and 1935 might have been depression-era unemployed engineers and surveyors not experienced in looking for ancient triangulation stations. The phrase "AT THE POINT WHERE THE TABLET SHOULD HAVE BEEN" seems to indicate that the person was looking for a disk and didn't find one, so marked it NOT FOUND.
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Deleting logs won't affect the NGS statistics columns, but it will probably affect the Geocaching.com column.
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Thanks for all of these great tools! I did notice a small discrepancy with the color coding legends for your recovery maps. The legend that is imbedded in the zoomify map says that orange is for 26-100 marks. While the legend on the left side of the website (shown below) says orange is for 25-100. It appears that the zoomify legend is correct (26 or more).
RF
Gee, it looks like 26 to me...
Fixed it! Thanks. -
Will you post the link to the county totals as well?
Oops, forgot to upload that file. It's there now. You can find it here.
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Still wondering what the "low rail" reference is. Any RR buffs out there know?
Is there any chance that the bridge is actually a viaduct carrying one railroad over another (or a former railroad)? In that case, one could interpret low rail as the set of tracks underneath the viaduct. Or perhaps there were at one time a set of double tracks not at the same level, one upslope and one downslope.
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I think headwall and capstone are usually features of arch bridges and tunnels. Here are the terms as I've seen them used.
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For some of the ones that I pictured, where the road crosses the stream at an angle, it is natural to orient oneself by the direction of the road centerline, rather than by the relation that the abutments have to themselves and the stream. That explains some of the cases where an abutment may be called "southeast" when in fact the abutments are almost parallel north and south, but skewed.
Here are two bridge illustrations from the benchmark wiki. The nomenclature was confirmed by several engineering and state bridge standards documents.
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Let's see... 25° F and the ground is still covered in snow. It won't qualify as "nice" here until mid-May or so.
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Most maps, mine included, don't show the minor islands because the inset would be almost as large as the continental US, or alternatively reduced in scale so that all the populated Hawaiian islands would be shrunken to insignificance. The Pacific is a BIG ocean.
You can look at the northernmost station for Hawaii and click on the Google maps link. You will see that the northernmost station of Hawaii is northwest of Midway island. DE5247 (Google map link).
edit: Here are the comparative sizes of Hawaii and the continental US:
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This thread made me curious about how accurate decriptions like "IN THE TOP OF THE SOUTH BACK WALL OF THE EAST ABUTMENT" have been for the places I've visited. My gut feeling was that they are not very accurate, given the number of times I've spent puzzling about which end of the bridge and which wingwall a mark should be on. Here's a rogue's gallery of bridges that I've encountered:
"IN THE TOP OF THE NORTHEAST END OF THE SOUTHEAST ABUTMENT" It would be clearer to call it the south end of the east abutment. It's hard to picture it as northeast of anything.
"IN THE TOP OF THE NORTH WING WALL, 10.5 FEET SOUTHWEST OF THE SOUTHWEST RAIL OF THE TRACK, AND 9 FEET NORTHWEST OF THE CENTER LINE OF THE ROAD" It was clearly wrong to say it was "NORTHWEST OF THE CENTER LINE OF THE ROAD" and that mistake may have contributed to the "NOT FOUND" report in 1954.
Originally "IN THE TOP OF THE SOUTHEAST END OF THE NORTHEAST ABUTMENT" which seems OK. Revised to "NORTH WEST END OF NORTH EAST ABUTMENT" by a later report. Uh, can we chip in and buy a fellow Geocacher a new compass?
Originally "IN THE TOP OF THE NORTH END OF THE EAST ABUTMENT", which seemed fine. Revised to "IN THE EAST END OF THE NORTH ABUTMENT" by later report
. I prefer the first, since there isn't really any north abutment on this bridge, only east and west ones, or perhaps northwest and southeast ones.
"IN THE TOP OF THE NORTHEAST END OF THE SOUTHEAST ABUTMENT". That's more reasonable for the magnetic directions than for true north directions.
"IN THE TOP OF THE SOUTHWEST WING WALL". Hardly. It's a real stretch of the imagination to call that southwest of anything.
"IN THE TOP OF THE NORTHEAST END OF THE SOUTHEAST ABUTMENT" Again, magnetic north seems more useful here. Otherwise I would have called it the north end of the east abutment.
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The February statistics have been posted to the statistics page. There were 678 recovery reports added to NGS datasheets. Remember that any reports for recoveries that were in 2007 were added to the 2007 column.
The maps have also been updated.
edit: oops, I see I put "January statistics" in the topic title. The new statistics are for February, of course.
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I've always assumed that a wedge was placed in the drill hole so that it would spread the notched bottom of the stem for a snug fit. Is that true, or is the notch on the stem just there to keep the disk from rotating once it has been cemented in?
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It looks like there is an upload every four to six weeks, at irregular intervals. For those who have recoveries showing for 2008, do you recall what date you sent them to NGS? I'm thinking NGS does one upload per month, sometime during the first of second week of a month.
The last report that was included in the statistics was a single report for Jan 16. All the other reports were from Jan 13 or earlier.
Fixed it! Thanks.
. I prefer the first, since there isn't really any north abutment on this bridge, only east and west ones, or perhaps northwest and southeast ones.
April Statistics
in Benchmarking
Posted
There were no GEOCAC recovery reports added to the NGS datasheets in April. It looks like there is a backlog for updates.
I've updated the statistics page with the new Geocaching log counts. Since there were no new NGS reports, I did not update the maps.