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How to measure approximate elevation differences?


TillaMurphs

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We often see NGS datasheet recovery logs that say something akin to:

 

The mark is 9 feet above the road.”

or

RM1 is 3 feet below the station mark.

 

Is there an easy way to verify these approximate height differences when we go to recover a mark? When the two points referenced are horizontally some distance apart, or have irregular terrain between them, we are wondering how to do this for comparing with previous recoveries or writing new ones.

 

At work I sometimes use a Wild N3 optical scope to measure and compare up to 100 different points within a thousandth of an inch. I am looking for something at the other end of the spectrum: Is there is a simple, inexpensive, quick to use, handheld device or procedure that we could use to verify or make elevation comparisons accurate enough to verify elevation differences such as the 9 and 3 foot examples above? I am thinking that accuracy would only need to be in the ballpark of 1/3-of-a-foot over 30 feet horizontal distance or something like that.

 

Thanks,

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Transparent aquarium hose with water in it.

 

A laser pointer and a long level.

Hi BDT,

 

Thanks for the ideas!

 

I have used a water hose with transparent ends to level fences before and it worked great. The problem is I don't have room for a 40 foot hose (with water) in the benchmarking backpack. :mad:

Incorporating a laser level sounds interesting. I am trying to avoid setting up a tripod, but maybe I can't get away from that.

 

I also tried using the inclinometer on my compass, but that didn't work out.

 

Thank you.

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I would use a hand level, tape measure and a line rod.

 

Place line rod at mark, locate myself with the hand level so it was level with the road and then observe the line rod. Since the line rods are grad in 1 ft increments you can get fairly close. If I had a helper I would use a level rod and not worry about getting level with the road first.

 

Another thing I often did when I was alone was place a nail in the shoulder, hook the non-metallic tape on it and go to the mark and use the tape as a level line and make adjustments for road crown if need be.

 

The closest foot is good enough as you are just trying refine the marks location in reference to the major features.

Edited by Z15
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There must be a way to adapt one of those relatively inexpensive laser levelers that are sold in hardware stores for quick alinement of picture frames and the like for under $100. I see a few in the $20 range and several in the $30-$35 range. These things are not always super precise and the visible range and pattern of the laser might be considerations.

 

Set it up on some kind of stake, level it. Read the line on a vertical rule on each end and subtract the foreward point from the back point readings to get the change in elevation.

 

- jlw

Edited by jwahl
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There must be a way to adapt one of those relatively inexpensive laser levelers that are sold in hardware stores for quick alinement of picture frames and the like for under $100. I see a few in the $20 range and several in the $30-$35 range. These things are not always super precise and the visible range and pattern of the laser might be considerations.

 

Set it up on some kind of stake, level it. Read the line on a vertical rule on each end and subtract the foreward point from the back point readings to get the change in elevation.

 

- jlw

 

A few years ago I got a Bushnell level for Christmas. This device comes with two lenses that create a line or cross in addition to a straight beam. I set it up in my yard and checked it with a water level. My water level consisted of a 50 foot garden hose with clear sections on the ends. With the sprit level in the top set to as level as I could; I set the near end of the water level as close to the height of the laser beam as I could by eye. The beam was pointed at the far end of water level about 40 feet away. I found there was about two inches of vertical play in the alignment of the beam with no noticeable change in the sprit level. In other words the spirit level was not really sensitive enough. It needs a flatter curve in the glass.

 

Before the Bushnell I was playing with a really cheap level I bought at Radio Shack for less than $10. It was a standard level with a laser pointer in one end. I figured what do I have to lose fro $10? I put the batteries in it, turned the laser on and ponted it at the wall about 60 feet way. I then sighted down the long edge of the level and the laser spot was about two and a half feet off. Way too far off. So I fiddled with the laser and got it aligned somewhat better. The good laser levels are set up so the laser is a convenient distance above the surface it is sitting on, such as 1 inch. This one was set at some very strange distance. It did not come out to any kind of even distance in inches or metric.

 

I’ve considered making my own laser level. I would use one made out of wood. I would take off the metal end caps and run it through a table saw to cut a groove a half laser beam width deeper than one inch. I would then drill a hole in one end cap one inch from the bottom and the diameter of the laser beam. On the opposite end I would hollow it out to take the guts of a laser pointer. The laser diode would be set in the level to shine along the grove and out the hole in the opposite end cap. With that arrangement the laser beam has to be parallel to the base and side of the level body. Now the question is how sensitive is the spirit level? It must be very sensitive to be used over long distances with any accuracy.

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A typical carpenter's level has a bubble that can be centered (with great care and checking by swapping end for end on a level surface) to 5 minutes of arc or a little more, or a slope of 1 part in 500 to 700. That's an inch elevation in 40 to 60 feet.

 

For better than that, I will pull out my ebay purchase, an old Topcon level I got for $50. I already had the tripod. I figure I can hold 0.01 or 0.02 foot (1/8 or 1/4 inch) in 200 feet with its scratched lens and my old eyes.

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Edited by Bill93
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