On Saturday, 26 October 2019 19.39.14 EDT John Steele wrote: > USGS has used meters since the early 1800s. They simply multiply by > 3937/1200 or 1250/381 to give Survey or International feet according to > each State's preference as documented in their surveying laws and State > Plane Coordinate System. A few States just use meters. 50 States = 50 Ways > (more or less, sometimes, its hard to come up with 50 unique choices). The > Congress picked some non-ideal conversion constants in the Metric Act of > 1866 and the 1893 Mendenhall Order simply used them to define Customary, > the foot being 1200/3937 m from 1893 to 1959, when it was renamed the > Survey foot. It you want to express the foot exactly as a fraction of a > meter, you have use that form, otherwise you get a repeating decimal, > whereas the International foot is defined in only 4 decimal digits. > Congress made a poor choice. Bronze Yard #11 (the former US standard > measured considerably closer to the modern value, 0.9144 m, than the value > in the Metric Act of 1866 and Mendenhall Order, 3600/3937, as documented in > NIST SP 447. Short live the Survey foot. (Most people don't even know it > exists)
I'm a surveyor, so I know about the US survey foot. I also know about the Indian survey foot, which was used for surveying in India. The Indian survey foot is 1.3 ppm shorter than the international foot; the US survey foot is 2 ppm longer. Bezitopo and another program I'm writing (which isn't public yet) can be set to I/O data in meters or any of the three feet; lengths are always held internally in meters. I've been asked to export a file as LandXML, which knows about the international foot and the US survey foot, but not the Indian survey foot. I'm tempted to export in meters regardless. On Saturday, 26 October 2019 20.11.19 EDT Peter Goodyear wrote: > Having 50 States each with their own surveying coordinate system must surely > make things difficult. Especially when three States meet, or four if > Arizona, Colorado, New Mexico and Utah actually meet at a single point. Some states have two coordinate systems. I live in North Carolina, which has one coordinate system, but Georgia has two, Florida has a Lambert conic and two transverse Mercators, and Alaska has ten, including three different types. North Carolina's projection would be seriously out of scale if used in Maine and tilted in Nevada; Florida's eastern projection would not be accurately self-inverse if used in Hawaii. It makes things difficult only for surveyors who work in more than one state plane zone, particularly if a tract to be surveyed straddles a zone boundary. Pierre -- ve ka'a ro klaji la .romas. se jmaji _______________________________________________ USMA mailing list [email protected] https://lists.colostate.edu/cgi-bin/mailman/listinfo/usma
