California Surveyors Forums

Change is coming.


https://www.sandiegouniontribune.com/ne ... easurement

the press is embarrassingly supportive of poor choices ...

I am curious as to why is it a poor choice Peter?

Moving forward, do you fellows think we should add statement that our work is using the International Foot on future surveys? I am wondering what the actual impacts will be to day to day surveying. I haven't contemplated geodetic surveying.

Thoughts?

8810. The plane coordinates of a point on the earth's surface, to
be used in expressing the position or location of the point in the
appropriate zone of CCS27 or CCS83, shall consist of two distances,
expressed in feet and decimals of a foot or meters and decimals of a
meter. When the values are expressed in feet, the "U.S. Survey
foot," (one foot = 1200/3937 meters) shall be used as the standard
foot for CCS27 and CCS83. One of these distances, to be known as the
"East x-coordinate," shall give the distance east of the Y axis; the
other, to be known as the "North y-coordinate," shall give the
distance north of the X axis. The Y axis of any zone shall be
parallel with the central meridian of that zone. The X axis of any
zone shall be at right angles to the central meridian of that zone.

And this:

Key excerpts:

The State Plane Coordinate System of 1927 was published in a unit of measure identified as the "U.S. Survey Foot." By 1959, except for surveying and mapping applications, the United States had switched to the unit of measure identified as the "International Foot."
(In 1983) the U.S. Survey Foot was specified in 11 states and the International Foot was specified in 6 states. In all other states the meter is the only referenced unit of measure in the SPCS 83 legislation. The remaining 19 states do not yet have any legislation concerning SPCS 83.
Because SPCS 83 is presently published by NGS only in meters, many surveyors, mappers, engineers, and LIS users are converting these metric values to feet. [..] there have been instances where the conversions were done using the wrong conversion factor or the computation was otherwise done incorrectly.

It would be nice if CLSA put out a technical paper or a white paper on this topic.

wonder what i do with my 100 foot lufkin tape. will all this make a difference?

Good question. Probably not, of course. it would be nice to consider all the issues.

PS, Happy holidays!

The article quoted Michael Dennis, a project manager for NOAA’s National Geodetic Survey: "Dennis also relayed a horror story one surveyor sent him: A contractor from a state that uses the U.S. foot planned a building in the glide path of a major airport in a state that uses the international foot. The confusion over the two different feet caused delays, extra cost and redesign of the building to be one floor shorter. (Dennis wouldn’t identify the airport.)"

Do you really think that's true? Wouldn't the discrepancy be at most 0.001' for a 1700' tall building, which is a super tall building?

It's the difference in the large state plane coordinates that cause the problems.

If they scaled their coordinates from 0,0 there is approximately 13' difference between the 1200/3937 vs. .3048 definition of a foot. This would have a large impact, if the building was designed to be just outside one of the many 3D protection zones surrounding an airport.

Moving forward, I don't believe we'd have to put "international foot" on our surveys, because if someone is using the new state plane projection, it should be stated within the new projection definition in our Public Resource Code. If we are tying into old geodetic surveys, we should note the definition of foot used.

Approximately, in 3 miles there is 0.02' difference from the definition. I will be the first to admit I do not believe any of my 3 mile measurements are accurate +/- 0.02'. I'd love to get a 1:800,000 closure on a traverse.

1500.000 m = 4921.26 Intl. ft. = 4921.25 US ft

At a local level, it doesn't make much difference. Within the area of a section, or a few sections, the differences would probably be less than the sizes of your error ellipses resulting from very careful field work.

It makes a difference when converting SPCs where the differences are several feet. (500,000.000 m = 1,640,419.95 Intl. ft = 1,640,416.67 US ft)
For most projects, using the "wrong" foot won't make a difference as it relates to other points of the project, but will create an apparent shift of the project coordinates by several feet as a conversion error.

Several years ago, we were locating microwave transmission, reception, and reflector sites for a major communications company. The tower & antenna locations had to be reported in SPCs. One of our techs converted several stations using the international foot rather than the US Survey foot and it created positional reporting errors of 8' to 14' for a group of scattered sites. In that context, it was a problem.

I am not supportive of this, anymore than converting to the metric system adopted by the government (and then reversed). Some things, just simply need to be left alone (like daylight savings time).

Angels dancing on the head of a pin.

On a webinar recently, Michael Dennis had a slide that showed 40 states (and territories?) that mandate in one way, shape or form the use of the U.S. Survey Foot while 6 mandate the International foot and the rest allow for both or are silent.

He is interested in NGS being consistent with other standards for other industries that mandate the international foot.

The problem is those other industries typically don't work with distances in the millions where the difference is significant.

Where does this come into play for surveyors in states that currently mandate the U.S. Survey Foot for SPCs? Any project already started on the U.S. Survey Foot, Any GIS based on the Survey Foot, and Legacy Record Maps.

IMO, This means that NGS will only publish in 2022 SPCs coordinates in the International Foot and organizations can either use those or convert to the U.S. Survey Foot as they see fit.

I prefer that they publish both and any utility they have work in both. Also, if The Public Resources Code is changed to reflect the international Foot and you don't want to use that then simply do not describe your coordinates as SPCs.

BTW, I also think we should pick one time standard and stick with it. Either/or for me, but pick one and stick with it.

Well said; well said!