surgent wrote:Re: sea level... since that can change hourly with the tides, there is no "surveyor's origin" for sea level that I know of.

Of course there is, it's called the National Geodetic Vertical Datum of 1929. Over a period of 18.6 years (which is a complete cycle of tides), 26 tidal gauges situated around the country established sea level. It was imperfect, but more than good enough for local control. The main problem was that sea level in New York is different from sea level in LA, for instance. It has been replaced by the North American Vertical Datum of 1988, which is used by gps units.

One of the gauges, Tidal 8, is located in San Pedro. I started a level run there, once. It was orgasmic.

What sealevel gauge is used to determine Himalaya altitudes ? How does it differ from the North America Vertical Datum asuming they are not the same ?

All elevations relate to whatever datum they are based upon. In the age of GPS all elevations are based on whatever the latest geoid happens to be. Wikipedia ha a good article on the geoid if you are really interested.

mattyj wrote:As someone who's worked with the National Elevation Dataset recently, I want to explain this a bit more. For most parts of the country, the NED comes in 1/3 arc-second resolution, approx. 30 ft.

Thanks for that explanation, I didn't know that the US NED data were that accurate.


I've spent a lot of time using Google Earth and Google maps terrain view, both for European and South American mountain ranges. One of my reasons would be to find the location and elevation of a particular summit.

In the beginning, I took the data provided at face value, but after a while, I started noticing discrepancies, both with printed maps and with what I saw with my own eyes, out in the field. I found mountains that showed only one summit, while I knew there were several. And I saw elevations in Google Earth or Terrain view that were much lower than the maps or guidebooks said they were, especially for sharp peaks.

When I started to look for background information, I read about the inaccuracies resulting from sampling grid problems, but until recently, wasn´t quite sure what the grid size was. A friend helped me along the way, and I learned that the elevation data in South America is based on SRTM data, which, according to the SRTM site itself, has a sampling of 1 arc seconds, but outstide the US and Australia, the officially released data is only 3 arc seconds. I´m going out on a limb here and guess that the reason is something military. Anyway, 3 arc seconds implies a lattice of 90 m (270 ft) - at the equator that is, I won´t go into different latitudes. That's roughly one point per football field. Many summits are smaller than that, so it's very likely that the nearest SRTM sampling point is not quite on the summit itself. And the further away, the lower it probably is.

Having sampling points, the next step is to calculate elevations and contour lines. Enter interpolation algorithms. Although I don´t know the algorithm used by Google, looking at Google Earth, it seems to me that the elevation of any one particular point is based on more than only the four closest points.
However, no matter how good the algorithm, I can't see how anything but smoothly curved mountains with big summits could ever be interpolated even reasonably well. For jagged mountains and sharp spikes, there simply isn´t enough data. Only if the raw SRTM data is corrected before Google uses it, better results can be expected. I do not know to what extent such corrections are applied, but from what I saw, especially in South America, there is room for improvement, to put it mildly. A room the size of a football field.

Knowing all this, what does that mean for using Google Earth and Maps? If I don't have a good map, I still use it for summit elevations, but tend to take the value given by Google as a good starting point, a lower bound for the actual value. If I know that the summit is big, I tend to trust the value more. As for the location, if I have photos, I use them to help me pinpoint it. Sometimes, especially for a rocky summit on a glaciated peak, the satellite image is helpful too.


Links:
Shuttle Radar Topography Mission
Background on Google Earth (and SRTM)

The real question here is DO I HAVE TO GO UP LANGLEY BEFORE I RETIRE FROM MOUNTAINEERING?!

no

mrchad9 wrote:Thunderbolt is a point on the ridge. Of course, that says nothing about whether it is worth climbing or not, but IMHO it is not a summit.

Summit racist

As a person who has climbed most of the 'points' greater than 14,000 ft in California and who is also a licensed surveyor in this State I can tell you that the exact, or even approximate, elevation of a peak is not something anyone is going to put a lot of effort into determining to the inch. Consider Thunderboldt Peak, as an example. The summit block is what? 20 feet tall. Who is going to go to the trouble of exactly determining the top of that block? Its official elevation is approximated because no one cares enough to measure it precisely. Same with other peaks, 14,000 feet or 11,000 feet. With regard to the sea level question. The US Army Corps of Engineers did an exhaustive study around 1900 down in Galveston Texas (of all places) and came up with a standardized mean sea level baseline for the whole country. Needless to say, comparing US elevations to elevations in other parts of the world is problematic.

The National Elevation Data set that they are using is a raster dataset with a resolution of either 10m or 30m in most places throughout the USA. That is, one elevation for a box that is 10m x 10m or one elevation for a box that is 30m x 30m. It is not an accurate way to determine the elevation of a mountain, although it can be close if the mountain has a summit like Mt. Whitney or Longs Peak.

I do however enjoy how such minor data problems can become a big deal for people who care about arbitrary summit elevations. If we started measuring mountains based on the distance from the center of mass of the earth it would ruin everyone's peak bagging list, and make ecuador really popular.

Again, check the PID for Langley and other surveyed points. PIDs were revised a few years back with for the NED improvements and NAD88. Even with the satellite DEMs, they still depend on pegging relative measurements to surveyed points.

Unfkingbelievable already.... Who gives a flying ass fuck how accurate the elevation of these "points" sticking up into the higher reaches of the atmosphere are?

STFU, go climb em and enjoy the experience for what they have to offer. Not the cocktail party ego boosting notoriety that you may think it will bring of being a "14er".

You want to toot your horn now that these "peaks", "summits" or what the fk ever they are, are not 14ers? Then go and choose the most direct and difficult line any of these aspects has to offer. Hell, go FA one if the case may be. Believe me, each one has such a line that many which are posting here, would shit their pants upon looking up at and thinking about getting on. Do so, then you can talk some seriuos ass shit on Friday night at your weekly social cocktail gathering.



Over and Out,

The Chief wrote:Unfkingbelievable already.... Who gives a flying ass fuck how accurate the elevation of these "points" sticking up into the higher reaches of the atmosphere are?

STFU, go climb em and enjoy the experience for what they have to offer. Not the cocktail party ego boosting notoriety that you may think it will bring of being a "14er".

You want to toot your horn now that these "peaks", "summits" or what the fk ever they are, are not 14ers? Then go and choose the most direct and difficult line any of these aspects has to offer. Hell, go FA one if the case may be. Believe me, each one has such a line that many which are posting here, would shit their pants upon looking up at and thinking about getting on. Do so, then you can talk some seriuos ass shit on Friday night at your weekly social cocktail gathering.

Over and Out,

Rick, why do you feel the need to inject your trademark insults, chest-beating, and obscenities into a civil discussion related to climbing? If you're not interested, you're the one who should STFU. You're an embarrassment to the climbing community and to SMI.

Over and out.

C'mon Chief, thats what we do during the winter: argue over how many angels can dance on the summit block of Thunderboldt Peak

I tend to leave my pursuit of 14er lists to my rare visits to Colorado (easier there, no matter how many we have in CA). Here's my progress thus far:

1.



Check.


2.



Check.


3.



Check.


4.



Check.


5.



Check. Thanks, Chief!

Oh contrar Master Emblem pursuing Bobpiceckering, I am very interested in this thread and how some perceive/d these 14ers. Or should I say, what many thought were 14ers. The discussions here in are rather, should I say, humorous. Appears that the new data and fact that some of them are no longer 14ers, really pissed you off.

I also know for a fact that upon first reading my post above, you actually spit the entire mouthful of your mornings coffee all over your monitor screen in laughter. And, that deep down inside them crotchety 14er bagging and snow angle protractor tool bowels of yours, you really do respect my in depth, true, very relative, interesting & colorful consistent comments and opinions here on SP.



BTW, fishing was grand today over at the river.





Over and Out