Welcome, Guest. Please login or register.

Login with username, password and session length
Forums Search:  


Author Topic: Summit POI's  (Read 4781 times)

magellan

  • Jr. Member
  • **
  • Posts: 41
  • Karma: 0
    • View Profile
Summit POI's
« on: April 06, 2009, 09:32:45 AM »
Is there a place that I could find summit point of interests that I could load with the POI loader. It would be nice to get summit POI's for the entire US, but Idaho and Utah could do.

magellan

  • Jr. Member
  • **
  • Posts: 41
  • Karma: 0
    • View Profile
Re: Summit POI's
« Reply #1 on: April 06, 2009, 12:17:58 PM »
i looked on that site, and I am somewhat confused. On the topo maps (and even on the USGS website) it shows Borah Peak in Idaho at a 12510ft summit, but then it also says the highest point is 12662ft. Is there a reason that the summit is a different elevation from the highest points on some mountains? (Ex. -  http://geonames.usgs.gov/pls/gnispublic/f?p=116:3:1059039279243257::NO::P3_FID,P3_TITLE:378037%2CBorah%20Peak)

maps4gps

  • Expert Advisor
  • *****
  • Posts: 1524
  • Karma: 17
    • View Profile
Re: Summit POI's
« Reply #2 on: April 06, 2009, 01:10:50 PM »
A few posts about a year ago mentioned the lower elevations for many summits in the GNIS. 
I think the situation is:
A few years ago USGS went to creating elevations for all the features in the GNIS by obtaining an elevation for each location from the NED elevation data.  I find some of the GNIS locations are right on, many are off by hundreds of feet (or even hundreds of miles and in the ocean where it is obvious a school, church, fire station, etc. would not exist).  Most/all summits are higher than what is around them in all directions, therefore, any error in spatial location would result in a lower elevation being obtained from the NED/DEM database.

A quick check of about 20 GNIS summits with the DRGs of the 24ks, showed most were right on  or within 1 or 2 contour lines; 2 were 3-4 contour lines down from the summit; 1 was 7 down; and 1, for a 14,000+ ft peak, was 1200 feet off horizontally and 11 contours down from the summit.
 
Maybe a nice idea (for some reason), but unless the locations and NED are absolutely accurate, the results for some types of features are not as usefull as having elevations for a lesser number of features.

magellan

  • Jr. Member
  • **
  • Posts: 41
  • Karma: 0
    • View Profile
Re: Summit POI's
« Reply #3 on: April 06, 2009, 01:53:49 PM »
Now, when you say they were off, was the elevation off as well, or did it say (example) "12,000ft" at 9,000ft?

maps4gps

  • Expert Advisor
  • *****
  • Posts: 1524
  • Karma: 17
    • View Profile
Re: Summit POI's
« Reply #4 on: April 06, 2009, 03:06:07 PM »
The horizontal (lat/long) position is off (has different coords in the GNIS file than the location on the published paper map, or its DRG image).  Therefore, an elevation for a location that is not actually at the location (summit) is being obtained from the NED (elevation grid file) and that elevation is being assigned to the feature(summit) in the GNIS.  I would say some of this is expected and due to using non-dimensionally stable paper maps, the equipment/techniques that were available 20-30 years ago and what looks to be some transcribing errors (2 for a 7, etc).  I suppose the obvious errors still exist because funding is easier to come by for new projects and adding additional data than it is for correcting errors which would require many times more time to correct than it did to do the original 'in mass' input.
Also the GNIS was created as a reference to names and their (approximate) locations and not as a source of positions to make accurate maps.  What else is available for us to use? ??

magellan

  • Jr. Member
  • **
  • Posts: 41
  • Karma: 0
    • View Profile
Re: Summit POI's
« Reply #5 on: April 06, 2009, 10:08:00 PM »
I went to the site, but could not find and .GPX files t download into POI loader. Am I not looking in the right place?

magellan

  • Jr. Member
  • **
  • Posts: 41
  • Karma: 0
    • View Profile
Re: Summit POI's
« Reply #6 on: April 07, 2009, 07:01:17 PM »
Seems to work. Thanks much. Makes things a lot easier.

magellan

  • Jr. Member
  • **
  • Posts: 41
  • Karma: 0
    • View Profile
Re: Summit POI's
« Reply #7 on: April 09, 2009, 08:18:30 AM »
I loaded the summit POI's into mapsource (opened it) after using the .GPX converter. Works great, but the elevation is off. I set it to show elevation on the title. The elevation on the title is correct (eg - Borah Peak - 12,510ft), but when I go to the properties, it says a different elevation (eg - Borah peak says around 41,000ft). I looked in the .CSV file to see if it was grabbing the number from elsewhere, but could not find any. Any reason why this may be happening?

maps4gps

  • Expert Advisor
  • *****
  • Posts: 1524
  • Karma: 17
    • View Profile
Re: Summit POI's
« Reply #8 on: April 09, 2009, 08:43:20 AM »
Another meter to feet conversion is being done.  Did USGS return to using feet in the GNIS files rather than meters?

magellan

  • Jr. Member
  • **
  • Posts: 41
  • Karma: 0
    • View Profile
Re: Summit POI's
« Reply #9 on: April 09, 2009, 09:14:53 PM »
I did select feet when it gave me the option - and it shows feet in the title (eg - Borah peak - 12,510ft) but in the properties of the POI it had over 41,000 ft in the elevation space. That is what is confusing.

 

anything