evenfall
-
Posts
788 -
Joined
-
Last visited
Posts posted by evenfall
-
-
New York State
Do Not Damage...
Gotta love reverse psychology...
Proof of what an old acquaintance from NY,NY told me years ago. You can always tell a New Yorker, But you can't tell them much. In fact , if you wait, they may tell you.
He was right, He was telling me. It makes the damage appear to be a self fulfilling prophecy...
Rob
-
I would venture a guess that it was placed by the Navy in 1918, unstamped. It would appear to be a reference mark, but it is really hard to say. It seems to have been triangulated from the get go. It was said to replace a destroyed CGS station but there is nothing we can research on that. It does give a name however, so if someone wanted to write NGS and ask about Station WHITE POINT 2, near Admiral 11's coordinates they may have data on the lost station which may tell tale. The Station WHITE POINT 2, could not have been too old if it were a brass disc monumentation. 1918 was still a young age for brass discs... Perhaps that sidewalk was what did the previous station in. One can only wonder what the arrow may have been oriented towards in 1918.
It was triangulated to second order, meaning it must have had a good view of other stations, but no mention of a tower used for those observations.
It also has no references to recoveries in the 30's when the big push was on.
It has a nearby station assigned for use as an Azimuth Mark.
The Superseded control also suggests that the station was used in high order leveling in the NGVD 29 days as well.
The 1942 recovery does state the disc is "Not Stamped". The 1954 recovery discovers the stamping Admiral 11.
It has been certified as good for GPS Observations...
It is certainly unique, but I fear it does not tell us a lot about its mystery.
A cool find.
Rob
-
Question: Does ayone really expect me to believe that surveyors in 1934 could measure altitude accurately to a hundredth of an inch?!? Can anyone today measure altitude accurately to a hundredth of an inch?
I'd Keep that bridge. :-D
The accuracy you are observing is from the methodology of multiple observations of the same station, and a Least Squares Adjustment. Statistically accurate in a network to the precision you observe. Yes the accuracy in observation is very high. Geodetic observations were and continue to be rigorous. The highest of standards were followed and repeated. Even then.
The NGS website has several good papers about their methodologies:
http://66.102.7.104/unclesam?q=cache:m2rPB...t+Squares&hl=en (An html version of a pdf document)
There are others, Feel free to google if you're interested.
Rob
-
Well, What I think we can bank on with certainty is that what we think we know about any of this is ongoing and subject to change. Survey data is not alone, in that it left a record of what was thought best at a time in the past, which we must still somehow integrate into our modern models of thinking. That is in part what makes this subject such a wrangle to get one's mind around.
Many things are like this, and I cannot say what I would go with on global warming or cooling. We haven't been around long enough to know all of the come and go. If Ying and Yang are true, as my avatar might suggest, then the several Ice Ages the world was known to have had were also countered with an opposite age, and who knows if man could really influence it at all. The best we can do is be good stewards of today and set ourselves up for successful tomorrows.
At least we have the Vertical Datum Shift Phenomena under control. It's all about perspectives anyway.
Rob
-
Well, It's all relative, really Paul... But I was pretty sure the whole thing was leaning right until 92...
That's the year after NAVD 88 began to take effect!
Rob
-
It is remarkable to learn who is paying attention, and to what.
Congrats on a good day Art,
Rob
-
R_C, Like Spoo's setup you can add a Bladder, at least, it sounds like that is what Spoo has going on in his set up. It is just handy to reach for the Tube over your shoulder...
If you have a Pack you already like and would like to add a Hydration Bladder, here are a couple options:
Sport
http://www.camelbak.com/rec/cb_prod.cfm?ca...&product_id=396
Or Military Grade:
http://www.camelbak.com/mil/cb_prod.cfm?ca...&product_id=301
I own 2 different Military Grade Camelbaks. They are made from Cordura. One is a straight Bladder for work. I wear it daily. I fill it half full at night and toss it in the spare fridge, in the morning I add ice cubes in the summertime and top it off. I have extra water to replenish it in my lunch pail if need be. I have had it 3 years now and it is still like new. The only failures have been one bite shut off valve under hard regular use. That probably add to over Four or Five Thousand hours of use. The other is Mil Grade as well but I use it as more of a Day Pack, and on the Mountain Bike as well. I feel they have been a very good value for the price. While I have no experience with the sport models, they are similar, less expensive and will likely hold up well, but they are not constructed nearly as heavy.
Good luck with those, they are a great tools for packing and hunting Survey Markers.
Rob
-
Spoo,
This is probably a question best asked in the NGS Forum, but since you have asked...
http://forums.Groundspeak.com/GC/index.php?showforum=40 For Future Reference. Highly technical questions are probably better over there.
Anyway...
Both the Historians and Surveyors are correct. The Historians researched Survey data for their information. There is nowhere that the sea is level. If you could see the Oceans in a three dimensional way, they would look a lot like the Geoid models do, only with tidal and wind wave action added. Mean sea level at any given Tide Gauge is taken as an average. In the case of NGVD29, the averages of 26 Gauges were then averaged as well, and thought there was some heavy variance between all of them, they had to have one solid number to base all the elevation leveling on land.
So to answer you as most specifically as I can, Sea is level only accurate in relation to where the observations are taken, and those observations are averaged. You have a Sea Level near you on the East coast which will differ from what I would observe here on the West Coast. Both would be correct as it can be, for it's observed locale. Sea level is considered a "Mean" Average, but it is only true in a Local way, not in a Global one. The National Ocean Service of which NGS is a part, maintains data on Sea Level here:
http://co-ops.nos.noaa.gov/sltrends/sltrends.shtml
Today, we use a reference ellipsoid, and frequently updated models of the geoid, to derive elevations. These elevations which are the real ground are referred to as orthometric heights. This is a GPS method, and is formulaically given as h= N=H Where h= the ellipsoidal height, which is the reference frame the Satellites consider the average surface of the Earth without form, N= the Geoid Height were scientists have determined the gravitational surface of the Earth to be, and H= the Orthometric Heights, which are the actual physical elevations.
During the 80's as I said in my previous post, NGS undertook a massive project and re-leveled the entire United States, Optically, so as to derive the Basis for NAVD 88, and using the methods which derive it. This leveling, when taken with the ellipsoid and geoid references formulaically and least squares adjustments give us what we observe today.
Something interesting to note about leveling. You may have seen Differential Leveling diagrams here in the past. I think both Z15 and Geo have posted pictures. The diagrams show the "Path" which was taken to derive the elevations. It is important to be able to retrace the steps because leveling elevations has a "path dependent" outcome. Different paths taken will derive slightly different outcomes, so the paths must be observed when setting up the networks. This way the paths can be re-leveled a number of time the same way, and all the observations can be compared with a least squares adjustment so as to make them highly accurate themselves, and amongst other elevations in the Level Lines, Circuits and Base lines.
Rob
-
R_C,
Nice Trekking!
You may find that a Camelbak or some other brand of Hydration pack would be just what you need to carry the water and gear without compromise.
I wear a 70 oz Military Camelbak during the workday and it makes all the difference in the world. it is just a water bladder, and fits under my Survey Safety Vest. I have so many things to carry, having the water on my back is the best place. Just fill up and go.
Here are a couple options as a for instance:
http://www.camelbak.com/rec/cb_prod.cfm?ca...&product_id=354
http://www.camelbak.com/rec/cb_prod.cfm?ca...&product_id=309
If you prefer industrial quality Camelbak over sport quality, you'll find it here:
http://www.eagleindustries.com/MainProd.as...=21&SubCatID=64
Enjoy, Rob
-
NGVD29 was the datum in use when the original survey was done. The National Geodetic Vertical Datum of 1929 was a vertical datum based on leveling done which was averaged to Mean Sea Level, tied to local mean sea level at 26 tide stations along the east and west coasts of the United States, Canada and the Gulf of Mexico.
In 1978, NGS began a program to combine leveling surveys into a single least squares adjustment to provide improved heights for over 700,000 vertical control points throughout the United States. This adjustment was completed in June, 1991 and has been designated the North American Vertical Datum of 1988 (NAVD88). NGS selected the GRS80 Ellipsoid at a single station, the primary tidal benchmark at Father Point/Rimouski, Quebec, Canada, as the minimum-constraint datum point for NAVD88.
NGS no longer Supports NGVD29, but some areas of the country still use it.
If you play with the VERTCON program: http://www.ngs.noaa.gov/TOOLS/Vertcon/vertcon.html You will see the datum Shift between the NGVD29 and the NAVD88 Datum all over the country. There are places where the difference, or Datum Shift Varies by Feet, not Inches.
The Problem that NGVD29 had was that Mean Sea Level was never stable enough, the Average taken from all the Tide Gauges over the course of a year, or many years was subject to how much water was in the sea at any particular time, Constantly changing tides, and the Geoid models which were observing that gravity affects the oceans and isn't a static force. NAVD 88 Locks Vertical references to a more stable reference, and renders all the measurements across the continent in a more stable framework.
Rob
-
I feel a geocacher could ask to recover the station from the department which has the station in operation. You never know, you may get ushered to the roof with a full on explanation of how it works. It is the heart of control for all the survey in the area, and the keepers of these stations take pride in the accomplishments and their local programs. It could be an enjoyable time for all.
Some county sites have a lot of data on line for their control. You never know, you might enjoy inquiring. You might be surprised that they are enjoying that you have taken interest.
Here is a methodology we use to determine the ARP, or the HI; Height of Instrument with GPS:
http://www.ngs.noaa.gov/PROJECTS/GPSmanual...ons.htm#antenna
Good Luck,
Rob
-
John,
Klemmer makes a great point. A pipeline will wind up as a magnetic anomaly, especially if it is fuel. It is also notable that magnetic north is not static nor consistent across the country. Because of its continued movements, what you wrote on a paper in the past would be rendered inaccurate over time by nature. So it isn't stable enough for use.
Good eye on the transcription errors. All the old data was transcribed to computer by hand, and these errors, though rare, are being found all the time.
Good Hunting!
Rob
-
I like your Idea Art, and I attempted to field ideas a few months ago about possible ways of linking it here directly to the NGS database for a constantly updated, history of retired marks included copy here at geocaching. Unfortunately the thread soon went dead after a bunch of do nothing nay-sayers disagreed amongst themselves over any and every idea. Most people just avoided it like the plague.
Unfortunately Art, It would appear that the culture of this forum is basically to wax nostalgically for a day from the past, where all that was done was showing pictures and gloating over finds in 100 mile long threads that take 30 minutes to load in to the browser. Acting as if finding a survey marker was actually a miracle. *Yawn* Of course they had to use a tube of Ben Gay to heal from all the incessant Back Patting, from not actually patting other peoples backs, but from the great lengths they go to to pat their own.
If a new idea is introduced or anything that might be confirmed as progressive or forward thinking here, a tsunami wave of resistance rushed out to run that idea over before it takes hold. Some even think they would like to govern the way NGS performs it's mark recovery. I imagine that NGS would be held hostage on a sea of indecision while the geocachers determine if the person recovering is worthy of doing so.
I am not sure I can put my finger on it. Perhaps some want power and authority, some want to Run everything, some won't sign on with an idea unless it is their idea, some would probably say no to a dish of their favorite ice cream. Then there are the progressive ones who tired of sitting on their hands and created something on their own, and shared it. That was cool, and they didn't bother to ask permission.
The unfortunance here lies in the fact that some things that Benchmark Hunters could really use are controlled by Geocaching. Geocaching in all honesty is geared, customer service wise, towards greasing the squeaky wheels. There is no advantage to membership if all you want is Benchmark Hunt Game Data, and as we should know if we don't, A squeaky wheel system is a system where problems constantly take cuts in line ahead of other problems, Thus bumping older problems to the back burner and keeping them there.
The idea that it may take a unified effort to create an idea that will compel Jeremy to take action and create something new for the Bench Mark Gamers, or even alter, update of improve upon what has already been made, is seemingly widely resisted here. A good many have already given up and gone away. Heck, a lot of Surveyors even stopped by to help out, and gave up on these people after watching them resist what is true. But if you like Art, I see a profitable business venture in selling Ben Gay around here!
Sorry Art. I would love to see a lot of cool things happen here, but even in the other Geocaching forums, other folks go on about how oppressive the culture seems here. Even the Moderators have abandoned this forum. It is a true Orphan. An Island unto itself. You can't even get to Jeremy from here anymore... :-)
All I can say is thanks for being one of the forward thinkers Art. And good luck getting the improvements you would enjoy having.
Rob
-
This feature will likely not come to pass until Benchmark Hunters form a consensus, unite, and petition geocaching like a squeaky wheel needing greased. Alas they are a Passive group and think that if they wait forever it will simply be bestowed upon them as if by magic.
Sadly, they have taken no proactive attempt beyond feeling poorly over the lack of this feature...
I have recommended in the past that people who want this should email Geocaching directly and form a focus group to petition Jeremy in the Geocaching website forum. So far, few have wanted to put for such an effort, and went back to secretly wishing. Some have even said they think it will happen, maybe, eventually. They would rather wait while other squeaky wheels get greased.
I would love to be made wrong on this one. If I am, a lot of people will have something they have been asking for, for five four years now.
Good luck though.
-
What methods do professionals use to avoid these types of problems or would they be avoided all together through the use of distant (multi-kilometer) azimuth marks?
Yes, I did send Deb Brown a note on the box score errors.]
Surveyors don't use compasses for creating geodetic quality survey data. They used an instrument called a Theodolite to survey all those angles in to very high accuracy, using trigonometric methods.
Deb may not concur with errors you may have noted with a Compass in an area you noticed magnetic anomalies. The Box Scores are full of data which has been subject to a least squares adjustment as well and fit the model. There is no basis for trusting a Compass over Survey Data with Applied Mathematics.
Cool observation though.
Rob
-
Hey, Not Bad for a Troll there BD! I'm glad you have master the Icon clicking gig! Let's all crow for you! You Go! Show us what you got! Troll. Maybe someday you'll either burn out, or "Get It".
Rob
-
And Now a Little edification for all:
DATA ITEM: Current Survey Control
DISPLAYED: Always, but the HEIGHT may be blank if the station
is a horizontal control station only.
COMMENTS : Current Survey Control is identified by a '*' in cc8
and comes under the heading "*CURRENT SURVEY CONTROL"
The horizontal datum in use is the North American Datum of 1983
(NAD 83). This datum also defines ellipsoid vertical height.
The orthometric vertical datum in use is the North American
Vertical Datum of 1988 (NAVD 88).
NGS no longer adjusts projects to the NAD 27 or NGVD 29 datums.
Care should be taken not to "mix" current datum(s) with
past datum(s) within a project.
NAD83 (1986) indicates positions on the NAD83 datum for the
North American Adjustment, completed in 1986.
NAD83 (nnnn) indicates positions on the NAD83 datum for the
North American Adjustment, but readjusted to a State High
Accuracy Reference Network (HARN) on the date shown in (nnnn).
NAD83 (CORS) indicates positions which are part of the CORS
network.
There are various Horizontal Control sources, as specified below:
ADJUSTED = Least squares adjustment.
(Rounded to 5 decimal places.)
HD_HELD1 = Differentially corrected hand held GPS observations.
(Rounded to 2 decimal places.)
HD_HELD2 = Autonomous hand held GPS observations.
(Rounded to 1 decimal places.)
SCALED = Scaled from a topographic map.
(Rounded to 0 decimal places.)
NAVD 88 orthometric heights are displayed where available.
If there was a height for the station on the National Geodetic
Vertical Datum of 1929 (NGVD 29), then that height will be
displayed under SUPERSEDED SURVEY CONTROL.
There are various Vertical Control sources, as specified below:
ADJUSTED = Direct Digital Output from Least Squares Adjustment
of Precise Leveling.
(Rounded to 3 decimal places.)
ADJ UNCH = Manually Entered (and NOT verified) Output of
Least Squares Adjustment of Precise Leveling.
(Rounded to 3 decimal places.)
POSTED = Pre-1991 Precise Leveling Adjusted to
the NAVD 88 Network After Completion of
the NAVD 88 General Adjustment of 1991.
(Rounded to 3 decimal places.)
READJUST = Precise Leveling Readjusted as Required
by Crustal Motion or Other Cause.
(Rounded to 2 decimal places.)
N HEIGHT = Computed from Precise Leveling Connected
at Only One Published Bench Mark.
(Rounded to 2 decimal places.)
RESET = Reset Computation of Precise Leveling.
(Rounded to 2 decimal places.)
COMPUTED = Computed from Precise Leveling Using
Non-rigorous Adjustment Technique.
(Rounded to 2 decimal places.)
LEVELING = Precise Leveling Performed by Horizontal
Field Party.
(Rounded to 2 decimal places.)
H LEVEL = Level between control points not connected
to bench mark.
(Rounded to 1 decimal places.)
GPS OBS = Computed from GPS Observations.
(Rounded to 1 decimal places.)
VERT ANG = Computed from Vertical Angle Observations.
(Rounded to 1 decimal place;
If No Check, to 0 decimal places.)
SCALED = Scaled from a Topographic Map.
(Rounded to 0 decimal places.)
U HEIGHT = Unvalidated height from precise leveling
connected at only one NSRS point.
(Rounded to 2 decimal places.)
VERTCON = The NAVD 88 height was computed by applying the
VERTCON shift value to the NGVD 29 height.
(Rounded to 0 decimal places.)
NOTE: NAVD 88 and NGVD 29 heights in meters are
converted to U.S. Survey Feet by using the
conversion factor:
U.S. Survey Feet = (39.37 / 12.00) x meters
Height in feet is rounded to 1 less decimal
place than the corresponding height in meters.
-
By The way, I am not trying to be a Hater with you Guys, But I Have hinted plenty about being accurate in the Past. I have decided that being more direct with you will be more effective.
It really is important to speak clearly about these things, even in a Game, so that everyone learns and becomes better players. Knowing something which isn't correct isn't helpful, Not really. The truth about survey markers is still the truth whether you are playing a game or you are surveying with them.
We have plenty of time to help others in their understanding here, so lets make sure we give them our best.
Rob
-
Since the opening poster provided a link to the datasheet, that resolves which adjusted it is.
No, not really.
Blackdog said: "PP2586 is an ADJUSTED mark, so your GPS receiver should take you to within 10 feet or so of its position. If what you found is far from where your GPS says, then it isn't the monument."
He made no note of the type of survey. Those who do not research the links will be mislead, and they will not likely learn the fine points from the word Adjusted anyway. It is a common word on Datasheets. So BlackDog can smile if he likes, but he was still misleading in his statement. Just like he was about Missouri River Commission Survey Markers.
Most Horizontal Survey is Adjusted. If it isn't, Horizontal Survey won't usually qualify for inclusion in the Active Database. So is most vertical ... Mostly. But that does not address anything beyond performing a least squares equation on the position to accurize it in a network.
There is no point to saying adjusted, it is a usual given. "Adjusted" tells the user very little and if the habit is developed to not read beyond that word, then most of the information is lost. There is more to be learned from looking at a datasheet, determining the Type of survey data ascribed to the station by looking for the quality of the survey. The "Order" is where the action is. Listed next to the Horizontal Position or the Elevation.
Hopefully this will help "Adjust" everyone's understanding of this subject matter.
Rob
-
All survey marks are adjusted
Boy do things get complicated sometimes.....
John
Unfortunately Not all Stations are Adjusted, so what you are saying is not correct. I said most are usually Adjusted... In your attempt to correct me, you are now in error.
Case in point, the station 0.3 miles from the Station this thread is about, is NOT Adjusted.
PP1414 DESIGNATION - 827
PP1414 PID - PP1414
PP1414 STATE/COUNTY- MN/HENNEPIN
PP1414 USGS QUAD - ST PAUL WEST (1993)
PP1414
PP1414 *CURRENT SURVEY CONTROL
PP1414 ___________________________________________________________________
PP1414* NAD 83(1986)- 44 58 05. (N) 093 12 26. (W) SCALED
PP1414* NAVD 88 - 277.234 (meters) 909.56 (feet) POSTED
PP1414 ___________________________________________________________________
PP1414 GEOID HEIGHT- -27.16 (meters) GEOID99
PP1414 DYNAMIC HT - 277.230 (meters) 909.55 (feet) COMP
PP1414 MODELED GRAV- 980,581.8 (mgal) NAVD 88
PP1414
PP1414 VERT ORDER - * POSTED, Code E , SEE BELOW
PP1414
PP1414.The horizontal coordinates were scaled from a topographic map and have
PP1414.an estimated accuracy of +/- 6 seconds.
PP1414
PP1414.The orthometric height was determined by differential leveling
PP1414.and adjusted by the National Geodetic Survey in 1992.
PP1414.* This is a POSTED BENCH MARK height. Code E indicates a distribution
PP1414.rate of 4.1 thru 8.0 mm/km.
PP1414
PP1414.The geoid height was determined by GEOID99.
PP1414
PP1414.The dynamic height is computed by dividing the NAVD 88
PP1414.geopotential number by the normal gravity value computed on the
PP1414.Geodetic Reference System of 1980 (GRS 80) ellipsoid at 45
PP1414.degrees latitude (g = 980.6199 gals.).
PP1414
PP1414.The modeled gravity was interpolated from observed gravity values.
PP1414
PP1414; North East Units Estimated Accuracy
PP1414;SPC MN S - 318,980. 862,540. MT (+/- 180 meters Scaled)
PP1414
PP1414 SUPERSEDED SURVEY CONTROL
PP1414
PP1414 NGVD 29 - 277.182 (m) 909.39 (f) ADJ UNCH 2 0
PP1414
PP1414.Superseded values are not recommended for survey control.
PP1414.NGS no longer adjusts projects to the NAD 27 or NGVD 29 datums.
PP1414.See file dsdata.txt to determine how the superseded data were derived.
PP1414
PP1414_MARKER: DD = SURVEY DISK
PP1414_SETTING: 0 = UNSPECIFIED SETTING
PP1414_STAMPING: 827
PP1414_STABILITY: D = MARK OF QUESTIONABLE OR UNKNOWN STABILITY
PP1414
PP1414 HISTORY - Date Condition Recov. By
PP1414 HISTORY - UNK MONUMENTED
PP1414 HISTORY - 1966 GOOD MNDT
PP1414 HISTORY - 1987 GOOD USPSQD
PP1414
PP1414 STATION DESCRIPTION
PP1414
PP1414''DESCRIBED BY MN DEPT OF TRANSP 1966
PP1414''IN MINNEAPOLIS.
PP1414''MARK IS LOCATED AT THE HENNEPIN - RAMSEY COUNTY LINE BETWEEN ST. PAUL
PP1414''AND MINNEAPOLIS NEAR THE KSTP RADIO STATION, IN THE CENTERLINE OF
PP1414''EMERALD STREET, IN LINE WITH THE SOUTH CURB OF UNIVERSITY AVENUE,
PP1414''FLUSH WITH THE PAVEMENT.
PP1414
PP1414 STATION RECOVERY (1987)
PP1414
PP1414''RECOVERY NOTE BY US POWER SQUADRON 1987 (CAF)
PP1414''RECOVERED IN GOOD CONDITION.
Yup, Things sure can be complicated, sometimes. That is why it is important to be careful, Succinct, and Thorough in our attempts to give others accurate advice.
Rob
-
2oldfarts (the rockhounders) -Since the opening poster provided a link to the datasheet, that resolves which adjusted it is.
Yep!
I support being succinct. Clear in your communications. Even doing homework about Pipe Caps and Brass Discs is a good idea. Be as accurate as possible from the get go. You know, like using NAD 83. This way your answers are more helpful. Not misleading or confusing. It is not about what you "think" you know, or acting like Trolls, it is about helping the person asking, and those who may read the whole thing in hopes of learning something. It is important.
I would not turn angles with this station without surveying it in. It is severely view blocked for optical work, and since it's original markings are not viewable, it would be hard to determine the proper spot on it for an instrument set up. Subsequent construction of the water tower may have even disturbed it. Without surveying it in, there is no way to know. I would not trust the Second order quality in my professional opinion.
Rob
-
I can't describe the stone post, but I do have some other observations.
PP2586 is an ADJUSTED mark, so your GPS receiver should take you to within 10 feet or so of its position.
The mounting was done by the Missouri River Commission. Their monuments are often (always? sometimes?) an early type of disk.
Black Dog,
All Horizontal Survey Stations are Usually Adjusted. It is prerequisite to be included as having quality enough to be included in the NGS Database. Vertical Control is also most often found to be "Adjusted". Some Vertical Control can be found to be "Posted" as well.
So you have Horizontal Control Stations, and Vertical Control Stations... All most usually "Adjusted".
Which Kind are you referring to? the Term "Adjusted" is simply too Vague. What were you trying to say? PP0994 is in the same vicinity, 0.3 miles away, and it is "Adjusted" too
Wouldn't it be more clear to say it is either Horizontally Adjusted or Vertically Adjusted since "Adjusted" has only to do with the quality of the survey data?
The entire body Of the Missouri River Commission's work was done in the late 1800's before the advent of brass discs. From approximately 1884, and ended in 1902. http://aa179.cr.usgs.gov/1894maps/ So Ahhhhh... It would be safer to say that there were probably zero brass discs Monumented by the Commission. They Did have their own Pipe Cap Monument though. Pipe Caps were not an early type of a Disc Monument, They were Pipe Caps. Totally different animals.
Rob
-
Hi Patty,
A Quadrangle is a four sided Polygon. It can be both Concave or Convex, it can even be a rectangle, but a rectangle cannot be concave or Convex and still be defined as a rectangle, so it is not appropriate to the Mapping world. The Cartographers are flat mapping a convex surface so they use the term Quad or Quadrangle to best describe this, as it will allow for the variables the terrain and shape of the earth will throw at it.
A 7.5 minute Quad is displaying 7.5 minutes of Arc, in terms of curvature of Earth. In the Northern Hemisphere this will mean smaller at the top from the bottom, width wise. They should be fairly uniform in length. Appear rectangular, but not really be. A 15 minute Quad would be 4 times bigger than a 7.5. Maybe called a superquad but that is just a marketing term. It is still a quadrangle.
It is safest to stick with knowing they are all Quad Maps, and that the Minutes of Arc around the globe such as 7.5, 15, 30, etc will affect the width and height scale of the section of earth you will see. The Minutes of arc simply state the "swath size" of the earth you will see on the particular map scale being offered. The scale will then be representative of the size the paper they chose to print it on.
Oh and Patty, here's something you might enjoy:
http://www.lib.berkeley.edu/EART/CA/CA_125k/30_minute1.html
Some old 30 minute maps worthy of historical comparisons.
Rob
-
Well John,
The word which troubles you has been very well and very specifically designed and documented for use in the field which upon you play a game. Though you assume you are just playing a game, the terminology continues to be of the most use when it is used in the most succinct rather than most ambiguous ways, even among the game players.
Post after post the ambiguity continues. I am surprised you never realize it. But in your view, it would appear there is no game here beyond the way you play.
Your continuing complaint is simply one where you refuse to accept reality, and instead replace reality with a version which you prefer, and when others don't follow and fall in step with your thinking, you attempt to discredit or resort to these silly troll tutorials.
Mocking Reality and the People who prefer it isn't gaining you ground John. The Mocking is really a reflection. I'd like to see you reexamine your motives here and consider whether these troll like attacks are really lifting anything up around here. I think it would be a responsible gesture.
Please give it some consideration.
Rob
Change In Designation
in Benchmarking
Posted
In Seattle, there is a small Dam and Boat Locks called the Ballard Locks, which was built by the Army Corps of engineers in the early 1900's. it is located at what is considered Salmon bay and forms the headwaters for what is called the ship canal which is what the bay tapers off into as it becomes a cut towards Lake Union. Lake Union also has a cut in the N.E. corner of it which is also a Ship Canal, connecting it to Lake Washington.
http://www.nws.usace.army.mil/PublicMenu/M...gename=mainpage
The Army Corps regulates the Lake levels of Lakes Union and Washington with the Ballard Locks, and all along this channel, the Army Corps has placed Survey markers which are stamped in a similar fashion as those Art found. Usually a number followed by the designation USE. If you find a USE Station, My guess there is something to do with Hydrology that the Corps is working on (or has) nearby.
The Army Corps still operates the Ballard Locks, 24/7/365. Passage is free of charge as they operate primarily with water and gravity. The only time they have even been closed in their entire history is during 9/11 during the no fly period.
Rob