jef

Yeah but what about azimuth marks? Enquiring minds etc.

We can always add benchmarks that aren't in the d.b. by just making them virtual caches. However those just aren't as much fun as regular caches. Well, here's a way to make virtual caches in general much more interesting, so that they become a good alternative for the non-NGS benchmarks. First, add a new optional attribute for caches: a codeword lock. In order to log a cache as found, the seeker has to supply the correct codeword. Some caches already do this informally, via email to the hider; this would just make it enforcable. Two: any individual log entry or photo on a codeword-locked cache could be marked as locked, by either the seeker or the hider. These locked items would only be viewable by those who had found the cache. This would let people post photos of the find that include the codeword, without being spoilers or having to photoshop the word away. The way I'd implement the codeward checking is: elide all non-alphanumeric characters, pound to lower case, then test whether the seeker-supplied codeword is a *substring* of the hider-specified codeword. This lets the hider allow multiple different codewords by just putting them all in the string. Some examples of how I'd use this: What is the name of the bronze statue at N 37 52.304 W 122 15.408? What is on the benchmark at N 37 56.855 W 122 18.305? What was founded at N 37 52.387 W 122 15.379?

Could some of the extra disks have been reference marks and azimuth marks? These are placed near the main station mark to help find it, or reset it if it gets destroyed. The text should describe all of these auxiliary disks, where they are in relation to the station, and their last known condition. I'm not clear on the difference between a reference mark and an azimuth mark, maybe someone else can explain that.

Yesterday evening I looked through the local marks and picked out the ones which were "surveyed by classical geodetic methods", as opposed to the ones taken off a topo map and subject to the theorized +- 6 seconds roundoff error. I looked for five of the classical marks, and found three. In each case the GPS coordinates were dead on, within ten feet or less. I think this establishes that the roundoff theory is correct and the bad datum theory is not correct.

There aren't that many plane wreck sites, though. I was thinking about putting geocaches at or around the three near me. I like the highpointing idea, unfortunately most GPS receivers aren't very accurate in the vertical direction.

So, how hard would it be to implement a way for seekers to add new benchmarks not in the NGS DB? I suppose one problem with doing this is what happens if the official USGS DB does eventually get added? We would have duplicate entries, which would need to be merged or something.

That Mt. Whitney replica pin is pretty nice. I've never been up Whitney, else I'd certainly get one. The abovementioned Air Force marker (item 2102387984) might be a never-used blank. Note that there are no i.d. numbers engraved on it.

That's very interesting about the horizontal control stations! I'll have to check out the one nearest my house.

I rechecked HT0968, the one near my house, using NAD-27 CONUS. This time my GPS was indicating a spot 150 feet to the west, instead of 120 feet to the SE. So, I don't think it's a datum issue.

Ah, ok. I didn't realize there was a whole nother set of markers not in the db.

Right, that's the one I meant, Elias not Jeremy.

How do I figure out the PID for a benchmark I find? Is it supposed to appear on the disk? Here's a photo of one near the geocache PLAIN SIGHT at N 37° 47.632 W 122° 16.609: http://www.acme.com/jef/geocaching/plain_sight_1.JPG Is the PID for this "SEAFOOD"?

I know of at least three near my house that are not in the DB. Is there some procedure for adding them to our DB, or even to the official NGS DB?

There are at least three real official brass-disk benchmarks near my house that don't show up in the database. I'm interested in this question too.

You can restrict the search results to a ten mile radius by adding &dist=10 to the end of the search URL. I keep a link with that URL on my personal geocaching page.

I checked the one nearest my house in Berkeley using both the indicated NAD-83 datum and the usual WGS-84. Both times I was off by about 120 feet, in the same direction. I don't think it's a datum issue. The rounding problem that Jeremy posted about sounds more likely.