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NGS Webinar Apr 25 on the fate of the US Survey foot
jalbrz replied 4 years, 11 months ago 39 Members · 112 Replies
Hear-hear! Meters are not a problem for surveyors, but a big problem for construction contractors. Their brains (and machinery) are calibrated in feet. All their materials are dimensioned in feet, so do you soft convert or hard convert? Should a 12′ lane be 3.6576m or 3.7m? Is a 10 penny nail (3″ long) 7.62cm or 8cm long? What about rebar spacing?
Converting DOT Standard Specifications (thousands of pages) from feet to meters cost millions and took years. “Cost is one reason the U.S. has been slow to adopt the metric system. Converting technical drawings and operations manuals for complex equipment with many parts can take thousands of man-hours. NASA engineers, for example, recently reported that converting the space shuttle‘s relevant drawings, software and documentation to SI units would require $370 million — about half the cost of a typical space shuttle launch.”
Don’t get me started on metric boundary surveys. Contemplate this: [Ohio Administrative Code] “Bearings expressed in degrees, minutes and seconds and distances expressed in feet and decimal parts thereof on each course. If a metric equivalent distance is stated, it shall be stated to the third decimal place.” 0.001m = 0.003′, so the precision specification is now 3 times as tight. An unintended consequence? Practically speaking, the average landowner, confused as he was by a traditional (foot metric) deed, is even more befuddled when confronting a metric one.
US Survey vs. International Foot, meh, only two parts per million difference so construction and landowner folks won’t see the difference. Surveyors working with coordinate systems where the point of origin is a million feet from the situs must pay attention, but can easily rescale their project coordinates. It is odd to have 6 states mandating the International foot. Converting to the International Foot has been in the works a long time, see below:
Watching now. Lots of history so far. Hope he gets to the arguments for and against pretty soon.
.[email protected] is the best to use.
So the plan seems to be that the 2022 replacements for older SPC will all be international feet, unless someone comes up with an overriding reason to not switch. That is the only use where it is significant, since hardly anyone can repeat a measurement to 2 ppm.
The legislative issue is moot because the existing legislations tie the survey foot to NAD83, and new legislation to adopt 2022 can easily specify international feet. NGS will of course, support backward compatibility in converting between datums.
.I’m going to petition the Texas Legislature to return to the vara.
33-1/3″ FOR LIFE!
Actually, it dawns on me that I just read the State Statute a couple of days ago and the vara definition actually is included.
He said 1 chain = slightly less than 66 feet. If I’m calculating this correctly, if 1 chain = 66 int’l feet then 1 chain = 65.99987 US Survey Feet because an IF is slightly shorter than a USFt or do I have it backwards.
I would’ve thought the chain would be based on the US Survey Foot.
Chain defined as 66 U.S. Survey Feet per Ch. 2 of the 2009 Manual methinks.
In the late 1980s a new proprietor of the place I worked began requiring all notes be kept in feet and meters. Gawd what a clusterf#*k that was to keep notes with no dedicated column in the book for that.
All the IMan did was to flick the ft/meters option on the Topcon gun and record what was on the readout.
Then the office tech had to sit and go thru the notes and calculate the equivalent of feet vs meters for every entry as double check before beginning to enter everything by hand into COGO.
Then new proprietor would constantly berate everyone because of things taking so long to get anything on paper when at the same time he would go out and take a week to do jobs we had regularly been doing in a days field time.
I am totally against converting completely to metrics because it is not a good fix for Texas.
As far as what is involved with GPS, it will create a new need for updated software to handle the already decaying software we have because of all the other updates that did not include all GPS software.
A designed move to create end of life for existing systems.
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- Posted by: A Harris
In the late 1980s a new proprietor of the place I worked began requiring all notes be kept in feet and meters. Gawd what a clusterf#*k that was to keep notes with no dedicated column in the book for that.
All the IMan did was to flick the ft/meters option on the Topcon gun and record what was on the readout.
Then the office tech had to sit and go thru the notes and calculate the equivalent of feet vs meters for every entry as double check before beginning to enter everything by hand into COGO.
I am totally against converting completely to metrics because it is not a good fix for Texas.
As far as what is involved with GPS, it will create a new need for updated software to handle the already decaying software we have because of all the other updates that did not include all GPS software.
A designed move to create end of life for existing systems.
0.02
What you described was a very basic QC check at the time. The metric reading was taken to check if the numbers were not transposed or recorded in error. This was only checked if there was a large misclosure or suspected bust. Blunders usually involved distance readings caused by a variety of reasons.
It was no big deal or clusterf()ck to do this. No problem with recording in field book. No problem converting. Just basic QC involving early days of edm to sniff out busts in traverses. Very helpful, if your work was in remote areas with hard access that you had to revisit.
Maybe I’m missing something here about metric measurement.
It seems dangerous to me. A 2ppm difference is enough to go unnoticed. A coordinate value in of 1,000,000 feet will change by two feet with the wrong conversion applied. That’s a scary small value in terms of easy recognition but a dangerously large value in the context of precision surveying. The difference between a meter and a foot is easily noticed.
Personally I think it best for NGS to simply use meters and let end users make the conversion. This doesn’t mean that our projects must be metric, only that the products from NGS will be metric. Conversions can still be made for construction from meters to your flavor of feet.
Furthermore, it seems like an uphill change when the majority of States in the U. S. have formally adopted the US Survey Foot as an official unit of measure. Then again, I believe establishing standardized units is a role for the federal government over State governments, but sticking with meters more or less goes around the hill instead of over it.
From a software perspective I’m concerned about this. In our data collection software, users can select between meters, iFt and USft. In the future, when a user selects a SPCS2022 Zone, do we remove the option to select USft? I realize this is something we’ll have to work out internally, but it is a question that software vendors will need to resolve. For those working with legacy software (i.e. CAD), will the user be allowed to make the wrong selection when writing an XML file? The answer here is “yes”. It’s going to be messy. But I suppose, just like the common numbers for ellipsoid vs. orthometric, ITRF vs. NAD83, Grid vs. Ground, the 2ppm will just be another number savvy surveyors will know and be able to identify when retracing a surveyor who didn’t know the difference.
Just because, hypothetically speaking, NGS provides metric only coordinates, doesn’t mean your project can’t be in feet (US or International), and you can’t stake out 6″ water pipe and 24″ RCP for the contractor. It simply means that the geodetic language for conveying positions would be spoken in metric.
I would switch to meters in a flash, it would be so much simpler especially in Leica software (Cyclone). Like software traps (demented Swiss minds especially) where it assumes your XYZ file is meters but doesn’t tell you that anywhere.
Metric is great for measuring from A to B or anything where a precise number is needed but for things like contours and stationing the meter is too long for convenience. Also it only allows for dividing by ten for the next more precise unit which is fine for geodesists and Surveyors but not so great for carpentry except to say the millimeter is smaller than practical for most general Surveying tasks, the centimeter is larger than is desirable.
On a mathematical note, base on the significant digits, it is correct for both US survey and SI feet.
What @shawn-billings said. If NGS sticks with meters it will minimize the confusion. Local surveyors can survey in local units. It is more confusing to take an OPUS solution in International Feet and convert it to US Survey Feet than the comparable operation from meters to US Survey Feet. It’s about magnitude: if you mess up the conversion operation meters=>US feet, it’s easily noticeable. Not so much where Int’l Feet are involved.
So because of a bad experience 30+ years ago, metric doesn’t work in Texas. Because Texas is different. Us northerners just don’t appreciate what Texans go through to survey.
When I worked in Canada we would run levels by reading both sides of the rod at each TP. One side in metric, one side in feet. The area I was in had steep slopes so levelling involved a lot of turns. Alan is right, it was a basic thing people did to trap transcription errors, which were common in the days before data collectors.
As a Canadian, I asked my boss how the switch from imperial to Metric went for him, as an old guy. He said “It really wasn’t difficult at all, since Surveyors have always used decimal feet. Just had to learn a new unit.
https://www.youtube.com/watch?v=z5-s-4KPtD8
Thanks. Message sent.
I’m with the keep NGS on meters, leave feet alone. I don’t think anyone is going to push for a conversion to meters in the US anytime soon.
The funny thing is it may have been computers that crashed it the last time.
It became so simple to use feet and convert, why bother with the expense of converting everything, just do it as needed.
He may like it that way, but that’s terrible fuel efficiency!
.We typically work with large coordinate values and our projects often stretch several miles, so the difference in U.S. Survey Feet vs. International Feet definitely rears its ugly head at the most inopportune times. It has bit us more than once!
I was initially not pleased with the possible disappearance of the U.S. Survey Foot but since I watched the webinar, it does in fact make sense to retire it.
The only superior evidence is that which you haven’t yet found.
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