US Survey vs. International Feet

Arkansas uses US ft.

It fundamentally makes no difference, until you start using State Plane Coordinates. THEN you had better know!

N

https://surveyorconnect.com/threads/us-or-international-foot.257193/

DDSM:beer:
( I love this Bar )

I had the same question a few years ago, and Mark Mayer was kind enough to post this picture from an old POB article.

Sorry, I initially uploaded the wrong picture. Now I have both tables.

Dan B. Robison, post: 363047, member: 34 wrote: https://surveyorconnect.com/threads/us-or-international-foot.257193/

DDSM:beer:
( I love this Bar )

Thanks Dan! If this is a complete list, I found what I needed.

I found this on that link: "MA is a U.S. Survey Foot state. 6 states have legislatively adopted the International Foot for the conversion of State Plane Coordinates - Arizona, Michigan, Montana, North Dakota, Oregon and South Carolina. Utah had done that but later changed to U.S. Survey Feet. With the exceptions of Alabama, Alaska, Hawaii and Missouri which have no specific foot conversion legislated, all the rest of the states have adopted the U.S. Survey foot. The reference source for MA is Massachusetts General Laws, Part 1, Title XV, Chapter 97, Section 8 https://malegislature.gov/Laws/GeneralLaws/PartI/TitleXV/Chapter97/Section8 " -Post by base9geodesy

Jimmy Cleveland, post: 363050, member: 91 wrote: I had the same question a few years ago, and Mark Mayer was kind enough to post this picture from an old POB article.

Sorry, I initially uploaded the wrong picture. Now I have both tables.

Perfect!! Exactly what I was looking for.

Colorado is another State that used International Feet until around 1991(?) changed over to US Survey feet by statute. (thinking from memory, so I am only narrowing it down to the early '90s

I would NOT trust (in an absolute sense) any "sheet, list, or compilation" concerning this matter.

I see Plats, Projects, Designs, etc. expressed in either US Survey Feet or International Feet, OR WORSE, NOT expressly defined at all (just "FEET"), all the time.

I still deal with [very good] surveys (and some not so good), expressed in the "Salt Lake Survey Foot," including surveys 50-100 miles from Salt Lake City.

The ONLY course of action for the Professional Surveyor, is the CHECK, CHECK, and CHECK again.

Considering how many "surveyors" don't even consider environmental corrections (Temperature & barometric pressure) when using "Total Stations" (or getting the values from the local weather report), the variance between International Feet & US Survey Feet, is the least of my worries.

Of course the modifrikingfying of UTM and State Plane Coordinates is the area where this issue REALLY stands out. This problem is also compounded by folks who don't know the difference between an "elevation" and an Ellipsoid Height (or which one they should use to compute an "elevation factor." In fact, the current NGS Data Sheets STILL use the term "Elev Factor," to describe the "ellipsoid height factor."

Just because a "state" has adopted one unit or the other, doesn't mean that you can ASSUME that everybody got the memo, or paid any attention to it if they did.

End rant
Loyal

Loyal, post: 363062, member: 228 wrote: I would NOT trust (in an absolute sense) any "sheet, list, or compilation" concerning this matter.

I see Plats, Projects, Designs, etc. expressed in either US Survey Feet or International Feet, OR WORSE, NOT expressly defined at all (just "FEET"), all the time.

I still deal with [very good] surveys (and some not so good), expressed in the "Salt Lake Survey Foot," including surveys 50-100 miles from Salt Lake City.

The ONLY course of action for the Professional Surveyor, is the CHECK, CHECK, and CHECK again.

Considering how many "surveyors" don't even consider environmental corrections (Temperature & barometric pressure) when using "Total Stations" (or getting the values from the local weather report), the variance between International Feet & US Survey Feet, is the least of my worries.

Of course the modifrikingfying of UTM and State Plane Coordinates is the area where this issue REALLY stands out. This problem is also compounded by folks who don't know the difference between an "elevation" and an Ellipsoid Height (or which one they should use to compute an "elevation factor." In fact, the current NGS Data Sheets STILL use the term "Elev Factor," to describe the "ellipsoid height factor."

Just because a "state" has adopted one unit or the other, doesn't mean that you can ASSUME that everybody got the memo, or paid any attention to it if they did.

End rant
Loyal

"I would NOT trust (in an absolute sense) any "sheet, list, or compilation" concerning this matter."

Ditto - my City uses the wrong one for their GIS...

Loyal, post: 363062, member: 228 wrote: Just because a "state" has adopted one unit or the other, doesn't mean that you can ASSUME that everybody got the memo, or paid any attention to it if they did.

Loyal,
That would make a good slogan:
BEERLEG...GET THE MEMO!

DDSM:beer:

Tom Adams, post: 363058, member: 7285 wrote: Colorado is another State that used International Feet until around 1991(?) changed over to US Survey feet by statute. (thinking from memory, so I am only narrowing it down to the early '90s

Tom - my recollection is that Colorado was US survey foot and some legislator changed it to International with some rider. He probably thought it was bringing Colorado into the world community. It took a year or two to get it changed back.
I am also working from memory - so...we could both be wrong!

KScott, post: 363075, member: 1455 wrote: Tom - my recollection is that Colorado was US survey foot and some legislator changed it to International with some rider. He probably thought it was bringing Colorado into the world community. It took a year or two to get it changed back.
I am also working from memory - so...we could both be wrong!

I would bet you're right. I just remember us getting some projects done with State Plane Coordinates done in International Feet, in the early part of the 90's. I didn't know the background when I first saw it changed to US-Survey.

The error from using the wrong one is 10.160 parts per million or 1.016 parts per hundred thousand. Roughly speaking, that's about 1 foot in 19 miles or about a tenth per 10,000 feet.

MathTeacher, post: 363098, member: 7674 wrote: The error from using the wrong one

12 inches/ft * 2.54 cm/inch = 30.48 cm/ft = 3048/10000 meter/ft exactly
versus
12 inches/ft * 1 meter/39.37 inches = 1200/3937 exactly
~ 0.30480061... meter/ft
The ratio is exactly 0.999998 as can be shown by working the integer factors.
=

Which is 2 parts per million or about 1 foot in 95 miles. I messed up the calculation; thanks for correcting me.

MathTeacher, post: 363116, member: 7674 wrote: Which is 2 parts per million or about 1 foot in 95 miles. I messed up the calculation; thanks for correcting me.

But the problem isn't just local to the size of your survey if you are working with state plane it is the distance from the state plane origin. I have seen some goofy stuff due to having this wrong.

Drilldo, post: 363130, member: 8604 wrote: But the problem isn't just local to the size of your survey if you are working with state plane it is the distance from the state plane origin. I have seen some goofy stuff due to having this wrong.

Yes sir you are correct. I did some earlier gps spc using international feet 10 or 12 years ago. Went back close to a few of those small surveys using us survey feet and spc and cors. 3 to 4 feet coordinate differences blew my mind. My surveys were fine. They just weren't where I thought they were. It's the distance from the state plane origin that shows the difference. The origin could be several hundred miles away. After some heavy drinking I figured that out. The good is I keep all my raw gps data, so re-calculating coordinates were not a problem. All the projects were small boundary surveys. North, distances from section corner ties, and bearing and distances between corners were good. It was the location in the world that was wrong.

Beware civil 3d defaults to international, and not every firm has figured this out yet. I still get plans in ift. ND is survey for for nad27, but ift for nad83. Obviously nad27 is obsolete. SD is usft, montana is ift. These 3 I know.

My first run in was in RI. 3 firms performing layout work and one used I.Ft. We were the last and the building did not match the driveway by 1.1 feet. Nice and small RI...
What is the biggest difference in SPCS conversion from meters? I get about seven feet here.

Sent from my SM-G900V using Tapatalk

It's interesting how avoiding a potential problem in applied mathematics can create a different problem somewhere else. State plane coordinates are huge in order to keep everything in the first coordinate quadrant and, as a result, keep all the numbers positive. But, with a coordinate value of 1,000,000 and an error of 2 parts per million, using the wrong definition for a foot creates an error of 2 feet in the coordinate of the point.

Here's a good article on the problem: http://www.pobonline.com/articles/91189-from-the-ground-up-the-international-versus-u-s-survey-foot

In North Carolina, the origin is at (609,601.2199; 166,589.9922) meters, (E; N) format. In US survey feet, the origin is at (2,000,000.002; 546,553.999). In International Feet, the coordinates of the origin are (2,000,004.002; 546,555.093). Moving east or north from the origin creates larger coordinate errors while moving west or south results in smaller ones.