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jayhawk999

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Everything posted by jayhawk999

  1. travis: This monument you were looking for is most likely a PACS or SACS, a primary or secondary airport control station, and most of the PACS are very close to mostly active runways. You need very specific official reasons to get next to one obviously. This are used for precise surveys to generate navigation data for landing. We recently tried to get to DX3328 in Fullerton, California but were told rather pointedly "not on my aerodrome" and we had some semi-official reason.
  2. The accuracy of a conversion is not the same thing as the offset or shift between lat/long values in NAD 27 vs. NAD 83. The differences can be as much as 100 meters or so. For example here in California, Fullerton Airport Primary Airport Control Station DX3328 has about 83 meters offset from NAD 27 to NAD 83. This value may be accurate to 10 or so cm which is a different number.
  3. Slower Pace, I was trying to imply just what you have observed -- there is no practical difference between NAD 83 and WGS 84. NAD 27, however, is different. There can be a considerable difference in coordinate values in this older datum. GPS receivers allow for NAD 27 use as some detailed maps use this datum and no other maps are yet available in NAD 83 or WGS 84. If you want to explore in more detail issues and descriptions of various datums, both the NGS and NIMA web sites provide access to various documents. WWW.NGS.NOAA.GOV and WWW.NIMA.MIL The NIMA site has tr80-003 "Geodesy for the Layman" which helped me a lot.
  4. Slower Pace, I was trying to imply just what you have observed -- there is no practical difference between NAD 83 and WGS 84. NAD 27, however, is different. There can be a considerable difference in coordinate values in this older datum. GPS receivers allow for NAD 27 use as some detailed maps use this datum and no other maps are yet available in NAD 83 or WGS 84. If you want to explore in more detail issues and descriptions of various datums, both the NGS and NIMA web sites provide access to various documents. WWW.NGS.NOAA.GOV and WWW.NIMA.MIL The NIMA site has tr80-003 "Geodesy for the Layman" which helped me a lot.
  5. While in high school some 50 years ago, I worked one summer on a surveying crew (two boys and a man) laying out a new county farm-to-market road in central Kansas. To do this, it was and is necesary to tie the survey points to existing "monuments" or other markers. We used section (mile) stones buried during the Public Land Surveys of the 1880s or so. One of these stones was some 4 feet underground with a broken bottle on it. Apparently the original which had never been disturbed. The surveyor in charge, said it took about a full day to locate and bury each stone marker. To close out the day, the crew would down a pint of whiskey and break the bottle over the stone before finishing the burial. I wish I had had the presence of mind to save that bottle.
  6. See my comments on NAD 83 vs WGS 84 above. One milli-arc minute corresponds to about 1.9 meters in latitude over the US, so that is about the lower limit you could even hope for in a hand held receiver. That is why these units don't display any more digits. Translation to other formats is simple arithmetic: divide arc seconds by 60 to get fractional minutes, divide arc minutes by 60 to get fractional degrees etc.
  7. See my comments on NAD 83 vs WGS 84 above. One milli-arc minute corresponds to about 1.9 meters in latitude over the US, so that is about the lower limit you could even hope for in a hand held receiver. That is why these units don't display any more digits. Translation to other formats is simple arithmetic: divide arc seconds by 60 to get fractional minutes, divide arc minutes by 60 to get fractional degrees etc.
  8. As a practica matter, there is no difference between these two coordinate systems at the present time in North America. The difference amounts to about 1.5 meters at this time but the specifics depend on the exact location on the North American tectonic plate. The resolution of most receivers is about 1.8 meters so, you won't see any difference in any datum used. If you are pathologically curious, you can go to a NGS web site and calculate the exact differences. See www.ngs.noaa.gov/cgi-bin/htdp/htdp_pl.prl and enter the data as described. Have fun!!
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