Team Troglodyte

Strange Coordinate System

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Does anyone know what coordinate system is in use on this sign in a San Antonio park? I'm at least somewhat familiar with most coordinate systems, and I can't think of anything that matches this. So far no one in the SA caching community seems to have a clue either. For reference, here are the coordinates of the nearest cache: N 29° 29.906 W 098° 42.482 UTM: 14R E 528300 N 3263245. State plane doesn't seem to work either.

 

20160504_150945s.jpg

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I'm guessing it is a measured distance from a boundary line / point. We use a similar method to describe oil well locations within the lease section.

Josh / Team 150%

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Almost undoubtedly correct, but if the reference point is not given it's meaningless to someone trying to determine their position. And the reference to "GPS Coordinates" is odd since it seems it would have to be a system that is normally selectable in a typical GPS, and my Garmin 64 seems unable to digest it. I may have to try to find someone in the parks department that has some information (but I'm not optimistic about that happening). 

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This page mentions it.  I googled "northing and easting".

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A number of systems refer to northings, eastings, etc., including the relatively common UTM, but I can't find any that fit with the numbers on that post. 

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From what I read online, it seems Northings and Eastings are usually measured in meters.  Measuring in Google Earth, 13,731,996 meters south of the point is pretty close to the South pole.  Well, within 500 kilometers or so.  It could be slop in Google Earth measure and the roundness (or lack thereof) of the earth.  2,061,011 meters west of there is VERY close to the 120th line of longitude, off the coast of Baja.

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I think you're going in the right direction Larry. Looks like it may be Universal Polar Stereographic. When I try to convert, it comes very close to believable numbers and there are apparently some correction factors that need to dialed in to make things work just right. Not something the casual GPS or cell phone user is likely to be familiar with.

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Looks like my next puzzle cache will be in Universal Polar Stereographic coordinates! >:D

When I project from the south pole, 13,731,996 meters north along the 120th line of west longitude, THEN due east 2,061,011 meters, it comes out near Hamilton, about 250 kilometers (150 miles) north of San Antonio.

 

Edited by HoustonControl
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I emailed the San Antonio Parks Dept this morning and got this quick reply this afternoon.

This is state plane coordinats for the more expensive Survey grade GPS, not your less than hand helds.

The accuracy of the gps numbers are to the 1000 of an decimal inch, they geocachers would have to calculate it to what they use.

 

Coordinates for this spot for Geocaching is 29* 29’54.91” N

                                                                                       98* 42’30.71”W

                                                                                       872’ Elevation

 

This beta conversion tool gets you pretty close.

 

http://beta.ngs.noaa.gov/gtkweb/

 

Received another reply to say the conversion can be down via GoogleEarth.

 

I found another conversion tool but you have to enter the zone number which appears to be 4204. https://gis.tulaliptribes-nsn.gov/Home/FrequentlyAskedQuestions.aspx

 

More on the History of State Plane Coordinates. Used in the US. 

 

http://desktop.arcgis.com/en/arcmap/10.3/guide-books/map-projections/state-plane-coordinate-system.htm

Edited by SockPuppet
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Thanks for the research - lots of good info there. I particularly like the conversion tool link and that one gets bookmarked for possible future use.

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000 of a dec inch!  

That will make for a few geo emails to CO's of the future :D

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Food for thought:

After I saw the accuracy claim I called the surveyor I work with that surveys our deep water well locations (think surveying a spot 10,000' under water) subway tunnels, and surveys in the GPS systems on ships (ie he is one of the best surveyors in the world). He told me 2 things. The first is the most accurate survey possible is about 5 mm by waypoint averaging in 30 min increments over the course of the day to grab different satellite constellations and then performing post processing using tie in points for reference that have been surveyed multiple times over the years.  The second is that there really is no "survey grade" GPS. Without the post processing our handhelds pulling off GLONASS, GPS, WAZ, etc are just as accurate if left to waypoint average for the same length of time. Without post processing he says the best accuracy to expect is ~ 3 ft. I confirmed this as he surveyed our farm for us with me clearing survey lines. At the GPS points he waypoint averaged at for 30 minutes and then post processed I can match within 3 to 6 ft if I waypoint average for 3 minutes.

Team 150%

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I thought that claim by the parks department person sounded a little hard to believe. I had previously heard that the best accuracy was about one centimeter but it looks like it's a bit better than that. 

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Makes me appreciate the building achievements of the Ancient Civilizations that much more; Assuming the Ancients weren't helped by advanced intergalactic visitors, or future Us traveling back in time to mess with ourselves in the present. ;) 

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