[Talk-us] Peaks
Hello, I was looking at peaks in Glacier National Park. There are quite a few that have been imported from GNIS. NPS has also a database of such peaks. My issue is that the databases are not consistent. If I take for instance Mt Cleveland: GNIS: 48.925 , -113.8480556 3175m (10417ft) NPS: 48.9227541, -113.8472346 3190m (10466ft) That's a little bit more than 1/8 mile off horizontal and 50 ft off vertical. Is there any other source of information to try and figure out what is the correct data? Thanks, N. ___ Talk-us mailing list Talk-us@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-us
Re: [Talk-us] Peaks
I can't speak in regards to the horizontal error, but in regards to the vertical error, GNIS elevation is taken from the National Elevation Dataset (NED). The NED is a gridded dataset (30 meter posting I believe), and does not contain spot heights, which is what you want. In other words, the NED contains the *average* elevation for each grid cell, not the peak elevation. Mike On Sat, Oct 23, 2010 at 6:52 AM, Nakor nakor@gmail.com wrote: Hello, I was looking at peaks in Glacier National Park. There are quite a few that have been imported from GNIS. NPS has also a database of such peaks. My issue is that the databases are not consistent. If I take for instance Mt Cleveland: GNIS: 48.925 , -113.8480556 3175m (10417ft) NPS: 48.9227541, -113.8472346 3190m (10466ft) That's a little bit more than 1/8 mile off horizontal and 50 ft off vertical. Is there any other source of information to try and figure out what is the correct data? Thanks, N. ___ Talk-us mailing list Talk-us@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-us ___ Talk-us mailing list Talk-us@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-us
Re: [Talk-us] Peaks
On 10/23/2010 10:46 AM, Mike Thompson wrote: I can't speak in regards to the horizontal error, but in regards to the vertical error, GNIS elevation is taken from the National Elevation Dataset (NED). The NED is a gridded dataset (30 meter posting I believe), and does not contain spot heights, which is what you want. In other words, the NED contains the *average* elevation for each grid cell, not the peak elevation. Mike So it looks like NPS would be more accurate for vertical. On the other hand I looked at NAIP imagery which is quite well aligned if I trust the road tracks I took. On that one GNIS seems to be closer to the ridge than NPS. ___ Talk-us mailing list Talk-us@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-us
Re: [Talk-us] Peaks
For a more authoritative answer took to the National Geodetic survey (NGS) http://www.ngs.noaa.gov/cgi-bin/ds_pid.prl The Benchmark at the summit of Mt Cleveland has a PID of TM1009 Do note that the latitude and longitude are in DMS.SSS format not Decimal Degrees This benchmark was originally established in 1901 so you will find heights and lat/longs from several different measurement systems. These could be NGVD1929, NAD 1927, NAVD1988, NAD83, HARN, ., You should record both the horizontal and vertical measurement systems in OSM for whatever you use. C. On Sat, Oct 23, 2010 at 8:52 AM, Nakor nakor@gmail.com wrote: Hello, I was looking at peaks in Glacier National Park. There are quite a few that have been imported from GNIS. NPS has also a database of such peaks. My issue is that the databases are not consistent. If I take for instance Mt Cleveland: GNIS: 48.925 , -113.8480556 3175m (10417ft) NPS: 48.9227541, -113.8472346 3190m (10466ft) That's a little bit more than 1/8 mile off horizontal and 50 ft off vertical. Is there any other source of information to try and figure out what is the correct data? Thanks, N. ___ Talk-us mailing list Talk-us@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-us -- Carl Anderson, GISP cander...@spatialfocus.com carl.ander...@vadose.org ___ Talk-us mailing list Talk-us@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-us
Re: [Talk-us] Peaks
I recommend USGS maps. GNIS is based on some automatic processing. It's much lower on steep peaks. I found even more difference than your example. On 23 Oct 2010, at 5:52 , Nakor wrote: Hello, I was looking at peaks in Glacier National Park. There are quite a few that have been imported from GNIS. NPS has also a database of such peaks. My issue is that the databases are not consistent. If I take for instance Mt Cleveland: GNIS: 48.925 , -113.8480556 3175m (10417ft) NPS: 48.9227541, -113.8472346 3190m (10466ft) That's a little bit more than 1/8 mile off horizontal and 50 ft off vertical. Is there any other source of information to try and figure out what is the correct data? Thanks, N. ___ Talk-us mailing list Talk-us@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-us ___ Talk-us mailing list Talk-us@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-us
