I'm probably going to embarrass myself with some questions concerning the U.S. Survey Foot, however I was always told there are no stupid questions. Here we go!
- Are Total Stations and EDMs built to measure in U.S. Survey Feet?
- Are the acreages shown on very large pieces of land (e.g., land grants) calculated by using the International Foot to U.S. Survey Foot conversion if the grants were metes and bounds descriptions and never measured in the field?
- Are the acreages shown on any survey ever described as being derived from measurements using the U.S. Survey Foot?
1. EDMs essentially are measuring the speed of light, with time, and correcting for the density of the air. The distances are just a conversion, be they meters, inches, feet, etc
2. Smarter people can answer this for me, I'm still learning the big book
3. See number 2 above. Addendum:?ÿ You can select the conversions depending on the software you're using, but again see number two.?ÿ 😉
I did consider the software aspect of number one. I was thinking about the old days when I used EDMs mounted on theodolites. No data collectors.
The difference in length is 2 parts per million.?ÿ The only place in the average surveyor's practice where it matters is in State Plane Coordinates or similar projections where you are dealing with large numbers of feet.
1. It doesn't matter which foot the EDM is displaying unless it its specs say it is good to 2 ppm and you are carefully correcting for temperature, pressure, and humidity.
2. I'm guessing acreage is given by dividing square feet of either kind by 43560. Again, no one measures that precisely.
3. see #2.
1. EDMs measure in meters and convert to whichever foot you care to use. There is a setting. Find it. In any case, at distances typically measured using EDMS the difference is trivial.?ÿ 1000.000 Int'l Feet equals 999.998 US Survey Feet. 0.002' in 1000'. Your EDM can't measure that precisely?ÿ even if you are properly correcting for temperature and pressure.?ÿ ?ÿ
2. With that in mind it really doesn't matter whether you compute area using one foot or the other. Nor does it matter for boundary computations, etc.?ÿ
3. No. Nobody ever specifies which foot definition is being used in that context.?ÿ
The difference between the feet really only comes into play when you are computing state plane coordinates, whose magnitude is commonly in the millions.?ÿ
Now, for extra bonus points - A "chain" is said to be 66 feet. Is that International feet or US Feet??ÿ While you contemplate that, remember that the chain unit was in use well before the US foot was defined in the 1890's.?ÿ ?ÿ?ÿ
Actually the first definition of the US Foot relative to the Meter was in the Metric Act of July 28, 1866 (AKA The Kasson Act) which stipulated that 1 Meter = 39.37 inches (3.2808333... feet per meter).
I believe that the values in the Metric Act were intended to be somewhat approximate, but the 39.37 inches per Meter "stuck."
Loyal?ÿ
interesting. Nevertheless, the chain was in use well before 1866.?ÿ
Thanks to all for answering my questions! Sometimes people ask you questions and you think, "Um, I never really thought about that." Then you feel embarrassed because you've been doing something for such a long time, and you don't feel like an authority on the subject anymore. So the question posed to me, in regards to surveyors measuring in U.S. Survey Feet, was "Could you please tell me, do you also use square US survey foot as a measure of the area?" My response will be, "Yes." My reasoning will be, "There is a very small (two parts per million) difference between the U.S. Survey Foot and the International Foot. Calculating an area with that in mind should be acceptable except where very large distances are involved." Besides that reasoning, I believe it's customary in mathematics to stick with the same units. Any comments on that perspective? It's possible that the person asking the question is just interested in correctly labeling the resulting square footage.
. EDMs essentially are measuring the speed of light, with time, and correcting for the density of the air
Not quite...
EDM's are essentially wave counting tools. It emits light waves at multiple wave lengths and counts the integer number of wave lengths and sums them up, sending/receiving/counting/summing smaller wave lengths to get the total distance.
To illustrate for a distance of say, 1342.231 meters:
Send out wave length of 10,000 meters: number back - 0
Wave length, 1000m: number back - 1
Wave length, 100m: number back - 3
Wave length, 10m: back - 4
Wave length, 1m: back - 2
Wave length, 0.1m: back - 2
Wave length, 0.01m: back 3
Wave length, 0.001m: back - 1
Total distance is sum:
10,000 x 0
1,000 x 1
100 x 3
etc...
The summed meter distance is then converted to the units requested.
?ÿ
Fair. I wasn't describing the actual interval of the received phase in my simple and less accurate answer.?ÿ Id like to play with the old school stuff. I got started with new and not very long distance versions and feel I missed out on lots of fun and frustration for sure
See number 2.?ÿ ?ÿ ?ÿ;)
It doesn't work by counting cycles or wavelengths in a travel time interval.?ÿ It's ambiguity resolution, finding where the phase of the return is, fractionally in a cycle of each wavelength, and applying that to the previous answer, rather than summing.
for a distance of say, 1342.231 meters:
wave length 10,000 m: answer 0.13 wavelength implies ?ÿ ?ÿ ?ÿ ?ÿ ?ÿ?ÿ ~1300 meters
Wave length?ÿ 1000m: answer?ÿ 0.34 + N1 wavelengths?ÿ?ÿ?ÿ?ÿ?ÿ?ÿ?ÿ?ÿ?ÿ
?ÿ ?ÿ so it chooses between 340m, 1340m, 2340m, 3340m, etc =>?ÿ ~1340 meters
Wave length ?ÿ?ÿ 100m: answer 0.42 + N2?ÿ wavelengths 1142, 1242, 1342, 1442 ... =>?ÿ ~ 1342
Wave length ?ÿ ?ÿ 10m:?ÿ answer?ÿ 0.223 + N3 wavelengths?ÿ?ÿ?ÿ?ÿ?ÿ?ÿ =>?ÿ ~ 1342.23
Wave length ?ÿ ?ÿ ?ÿ 1m:?ÿ answer?ÿ 0.231 + N4 wavelengths?ÿ?ÿ?ÿ?ÿ?ÿ?ÿ =>?ÿ ?ÿ?ÿ 1342.231
Older EDM units had a shortest wavelength of 10 meters.?ÿ Newer ones are somewhat less, but not down to centimeters.?ÿ It all depends on a reference frequency standard to generate the signals. The speed of light, adjusted for temperature and pressure of air, is used to convert frequency to wavelength.
?ÿ
More precisely, these types of EDM instruments aren't using multiple wavelengths of light (either visible or infrared), but rather different wavelengths of signals modulated onto the beam of light.
When I was using a Topcon instrument-mounted (on a Wild T16) EDM back in 1988, I had to dial a knob until a string of flashing red lights became steady before I took a measurement. What was happening as I was dialing the knob?
I don't know anything specific to that instrument, but I'd guess it was similar to a manual version of the sequence I posted above.
Yay Physics!!!!!!!
This thread is a good example of why ALL SURVEYOR'S MEASURE DIFFERENTLY.?ÿ Caps for emphasis or those hard of hearing.?ÿ Exactness in measurement is like economists talking about free markets.?ÿ Neither exists, someone somewhere always has their thumb on the wrong button.
So the measuring wave length is meters. And the measuring wave modulated on a carrier wave is by an oscillator in Hertz. So the EDM??s base unit is time.?ÿ
If we all measure differently, then why is it that my EDM agrees with the local CBL, and phase differential post-processed gps baseline (much better than 10 PPM)?
I can??t be measuring much different.?ÿ
At least for the max limit of my EDM of 10K ft.?ÿ
i believe that was adjusting the gain of the receiver. Like setting exposure on a digital camera ?ÿ(more or less the same)?ÿ
My trusty HP3805 had the same manual required adjustment. Centering a meter needle after adjusting for max signal return.?ÿ
