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LSUFan

Measurements taken from bridges questions?

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Hi everyone, I was able to get a little year-end benchmarking done today and ran into something at CQ1152 I don't guess I have encountered before. I was hoping ya could educate me for future reference, and ask for your shared wisdom.

 

http://www.ngs.noaa.gov/cgi-bin/ds_mark.prl?PidBox=CQ1152

 

The description for CQ1152 states the following:

 

IT IS 0.05 MILE SOUTHEAST OF THE BAYOU DARBONNE BRIDGE,

 

The measurement taken from the bridge states that the mark is 0.05 miles (or 264 feet).

 

My question is, if there is no point given in the description of where the measurement is taken from on the bridge (ie SE abutment, etc), is it standard practice for the measurement to be taken from the middle of the bridge?

 

We took a first measurement off the closest end of the bridge (which is a fairly long bridge). After an unsuccessful search utilizing the measurements from the main road and the bridge estimate..........I was luckily able to spot a witness post (you just got to love them) several hundred feet from our initial point of search. From where the mark was, the measurement would have had to be taken from the middle of the bridge to be 264 feet, as we weren't even close taking a measurement from the end.

 

I couldn't confirm the actual 264 feet measurement from the centerpoint due to the length of the bridge and dangerous traffic conditions, but it looked real close just eyeballing it.

 

As I stated, I don't guess I have had this pop up before in my searches, as the measurements are usually from an end or an abutment on bridges.....and was just wondering if this is something standard. If so, is the measurement taken from the exact center of the bridge?

 

Thanks in advance for any help.

 

Bobby

Edited by LSUFan

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IMO the mileage is not precise enough to convert it to feet, its a approximate.

 

Since it not stated in the description, where the mileage was taken from is unknown. It could be from anywhere on the bridge, if they would have measured it I think they would have stated where from.

 

IMO

Edited by Z15

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IMO the mileage is not precise enough to convert it to feet, its a approximate.

 

Since it not stated in the description, where the mileage was taken from is unknown. It could be from anywhere on the bridge, if they would have measured it I think they would have stated where from.

 

IMO

 

Thanks Z15, it does make more sense as an approximate, but I still was wondering if there is any sort of set rules as to where the approximation was set from if not listed in the description. This was a first for me.

 

I will be back by there New Years Day, and besides the handheld coords I have now, I may take some better approximate measurements off the SE 'end' of the bridge to add to the description for my recovery report submittal.

 

This mark is located on one of those roads with a bunch of others that show up white (no reports) on Scaredy Cats viewer.........and you just have to go see if you can change their status color. LOL

Edited by LSUFan

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They could have even scaled it off a map just to have a general location. Its purposely vague maybe because the info was not provided by the field party.

 

No rules that I am aware of, just experience. Often time rules are not followed anyway.

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Most of the measurements I have seen are from the middle of things, but those things have usually been small things like roads and trees. I don't recall such a specific measurement from a bridge. Like you I would have assumed it was from the closest end of the bridge, but also like I wouldn't have ruled out the center of the bridge.

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Using Google Earth I measure the bridge at 742.32 ft. or 0.14 miles long which is more than twice the distance “from the bridge to the mark”. So it would seem the center of the bridge is not the point measured from.

 

Did you get a GPS location for the mark?

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Using Google Earth I measure the bridge at 742.32 ft. or 0.14 miles long which is more than twice the distance “from the bridge to the mark”. So it would seem the center of the bridge is not the point measured from.

 

Did you get a GPS location for the mark?

 

Yes, I got Handheld coords but can't seem to find my notebook currently with them that I wrote them in. I was camping with friends at the time, and the pad may be in my RV. I'll go thru it more this evening and try to find it.

 

The mark is a whole lot closer to the SW corner of the SE end of the bridge than what it currently shows with the scaled coords.

 

Thanks for the bridge measurements.

Edited by LSUFan

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I haven't come across that before, but I'll throw my (generally useless) opinion into the mix.

 

I look at this in two ways: How would I READ that datasheet, and How would I WRITE that datasheet?

 

If I were reading a datasheet with that wording, I'd be confused. The typical way to write that would be to give a specific place from which the measurement was being made. I wouldn't expect it to say that it was measured from an exact point, but I would expect at least a general structure (a corner or something). If I were reading it and it didn't say exactly where it was measured from, I'd automatically assume they meant the exact center of the bridge. For some reason, my mind would automatically treat the bridge as a single object and would reduce it down to a point mass located at the center of the object. I'm overly analytical like that.

 

If I were writing the datasheet, there's no way in the world I would write it the way it's written. When taking measurements in the field I always try to measure from the objects in the area that I expect to be the most permanent. I always go with the corners of buildings, a rail of a railroad track (measured perpindicularly from the track), sometimes trees, sometimes telephone poles, occasionally I'll use the center of a road. I never use the edge of a road for any measurement, though I've certainly seen plenty of datasheets that do use them. For my money, they change too much over time.

 

That's my two cents.

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It seems that measurements are (usually) taken from the nearest point of a structure, from what I have seen, so probably from the SW corner of the bridge. It's not a 'precise' measure, tho....it's intended as 'directions to the station' not 'location of the mark'.

 

You need to use the other precise measurements (from highway, woods road, tree) to locate the mark.

Edited by revent

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Again using Google Earth I find it hard to locate the mark. There are two “woods roads” but both of them are too far down the road away from the bridge. Using Street View on Google Earth O can not find any sign of a “woods Road” and the tree may be gone after 40+ years. Other trees may have grown up to confuse the issue.

 

It is also possible the bridge has been rebuilt and is longer than the original. Guessing at the possible location of an older and shorter bridge I get coordinates of 32° 41.622'N 92° 33.128'W for the mark.

 

LSU fan you might check for a date on the bridge, see if it is newer than 1969.

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Again using Google Earth I find it hard to locate the mark. There are two “woods roads” but both of them are too far down the road away from the bridge. Using Street View on Google Earth O can not find any sign of a “woods Road” and the tree may be gone after 40+ years. Other trees may have grown up to confuse the issue.

 

It is also possible the bridge has been rebuilt and is longer than the original. Guessing at the possible location of an older and shorter bridge I get coordinates of 32° 41.622'N 92° 33.128'W for the mark.

 

LSU fan you might check for a date on the bridge, see if it is newer than 1969.

 

TBH, as it is a Louisiana Department of Highways mark, the 'authoritative' source would be to ask them. Er, "Louisiana Department of Highways and Transportation', these days.

http://gis.dotd.la.gov/Maps/BenchMarks.aspx

 

Nice map interface, popups give detailed info on marks. Be nice if Texas had a system like this... :/

Edited by revent

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