ArtMan Posted October 2, 2010 Posted October 2, 2010 I had a brief look today at The National Map, a digital project of the USGS. Among its many other features, it will return coordinates to three decimal places of seconds (e.g. 40 39 11.345) for a selected point. I checked a handful of locations in the Mid-Atlantic and Midwest, and it seems to be highly accurate, but I can't find any information on the nationalmap.gov site about the accuracy of coordinates. It seems that coordinates derived from this source might be more desirable than HH2 coordinates from our consumer-grade GPS receivers in logging on geocaching.com, and possibly also in reporting to NGS. Of course, the source should be indicated. Thoughts? ArtMan Quote
Papa-Bear-NYC Posted October 2, 2010 Posted October 2, 2010 I had a brief look today at The National Map, a digital project of the USGS. Among its many other features, it will return coordinates to three decimal places of seconds (e.g. 40 39 11.345) for a selected point. I checked a handful of locations in the Mid-Atlantic and Midwest, and it seems to be highly accurate, but I can't find any information on the nationalmap.gov site about the accuracy of coordinates. It seems that coordinates derived from this source might be more desirable than HH2 coordinates from our consumer-grade GPS receivers in logging on geocaching.com, and possibly also in reporting to NGS. Of course, the source should be indicated. Thoughts? ArtMan Isn't that built on data from volunteers in the National Map Corps (now defunct ??)? If so, it's based on HH GPS readings sent it by folks like you and me. Unless they also pulled some data from ortho-photos (like Google, Bing, etc.) which can be surprisingly accurate. There's only so many places the data could come for, and they certainly didn't have a professional surveyors with survey grade equipment on every street corner. Rg Quote
ArtMan Posted October 2, 2010 Author Posted October 2, 2010 I don't think the maps (aerial images) are georeferenced with volunteers' HH2 contributions. Please help me with some ground truth: pick out a couple of datasheets with adjusted coordinates where you have visited the location, and see if the National Map coordinates don't agree with the datasheets to a pretty high (better than HH2) degree of accuracy. Quote
+billwallace Posted October 3, 2010 Posted October 3, 2010 Hard to say.... can't really see where the disks are in the imagery. In one instance the triangle on the topo overlay was 7.6 feet off and in another it was 31 feet off. Quote
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