Jump to content

Rakusan

+Premium Members
  • Posts

    30
  • Joined

  • Last visited

Everything posted by Rakusan

  1. See, I've been telling you guys geodesy was important!
  2. Log out, log in ... log out again, log in ...
  3. "Sure, it can keep your broccoli fresh, but how does it hold up to being bounced around on a tether, in a flooded ditch." The idea of the Tupperware lady fielding that one ... ROFL! OTOH, I'd like to see Tupperware come out with a Geocachers' line of camo pieces.
  4. All this "rant" confirms me in the practice of describing my containers as well as using the micro/small/regular/large categories. Unless specifying the container is going to "spoil" the cache ... I'd rather tell you exactly what you're seeking. Seems like a good way to do things around here.
  5. Finding a cache is fun ... hiding a cache is sharing the fun. Getting an idea for a cache and making it work -- then reading the comments as people log in their finds -- that's even more fun, even when it's hard work and you're getting frustrated, or you realize that a cool scheme isn't going to work and you have to re-invent the dratted thing almost on the fly. There's the challenge, too, of "How can I make this difficult - or fun - or share this neat experience, this neat site, with the world?" But when you get it all together -- do the work, find the perfect (or a darned good) hiding place, place your little treasure and get it logged in -- that's cool. It's gratifying. And then you start getting those logs from visitors to your cache, little "Thank You" notes from this community ... or the snarls of frustration that are applause for a really well-hidden hide.
  6. My first use of GPS was as a teaching tool -- using it to demonstrate the differences between different geodetic datums, as part of my course on aeronautical cartography. Even professional cartographers could be surprised to see a huge difference between the "numbers" on two different datums, and they understood that it could be a matter of life-or-death for an air chart to be produced on the WGS84 system. I also have used my portable GPSr on my mountain bike, which is a surprise to some people. This was before I started geocaching, of course. I don't have time for biking now.
  7. I used PC-7 epoxy to attach a snap-in bracket to the top of a telescoping hiking staff. The GPSr is always upright for best reception; I don't have to fumble with it; and I can stab it into the ground to get a stable reading.
  8. This is once too many unless it works.
  9. Let's see how my new avatar looks.
  10. I bought a Minolta Dimage X20 as a second camera - it's sturdy, tiny, and runs on two AA batteries (same as your E-Trex). Fits in my shirt pocket. 2-megapixel images. Good lens (check imaging-resource.com for more on that). Price under $200 ... what's not to like? Something that helps make it rugged: Instead of a lens that telescopes out of the front of this camera, they mounted it as a 'periscope' that's enclosed safe inside the body at all times. Upgraded this summer to the "Dimage X31" - same body, periscope lens and AA-battery power, but a 3.1-megapixel imaging element. Still less than $200.
  11. Cold start can be very time-consuming. I had my airplane's Garmin GPS 155 TSO shut down for a year during some major repairs. When I finally had it hooked up again, it took OVER AN HOUR to re-acquire the GPS constellation and start locking on satellites.
  12. Every GPS unit - Garmin, Magellan, Lowrance, whatever - uses a firmware base map that stores each road in its memory as a chain of connected points. The 'accuracy' of the base map is compromised by the need to economize on memory, so they can't portray every bend and wiggle as well as a product like Topo USA.
  13. OTOH, this from the Aircraft Owners and Pilots Association ... http://www.aopa.org/whatsnew/newsitems/2004/041216space.html
  14. Rakusan

    Datums

    Sorry, Harry, but cartographers and geodesists DO use the word "datums". "Data" are raw material for generating information. "Datums" is the multiple of "datum" when we're referring to the "geodetic datum" - a mathematical model of the exact, or best-approximated, size and shape of the Earth.
  15. Pretty close ... The geodetic datum is not a "guess," but a mathematical approximation, based on a web of highly-accurate measurements of the relative positions of chosen points across a region, continent, or the entire world. These measurements are fitted together by painstaking computation, to determine the exact curvature that will be a best fit to the measured positions. Most of these datums (incidentally, "data" means raw material for computation whereas "datums" specifically means more than one of these mathematical models) were created for individual nations, and due to the way they're devised they don't fit together very well - it requires some fancy computation to "shift" a position determined on one datum to the coordinate system of another datum. After WWII, many international coalitions worked to tie together their geodetic networks and to devise a datum that covered continents ... for instance, the NATO nations, or South America. Part of the work of the International Geophysical Year (1957) was to find a way to tie the whole world into one geodetic whole. Then came the satellite ... and astronomers, geodesists, earth and space scientists learned to use their orbits to determine the actual mass center of the Earth. From that, they were able to fit the whole puzzle of these differing datums into a workable "average fit" that could be used worldwide ... first the World Geodetic System of 1966, then a refinement in 1972, and the present WGS of 1984. WGS 84 is the geodetic basis of the GPS system, because it is a good average fit ... but many older maps and charts have been made to fit the old local datum (such as the NAD 27, or North American Datum of 1927) and must be "datum-shifted" to fit the WGS 84. An extra headache for the cartographic sciences. Sorry to get pedantic on you ... geodesy is part of my profession.
  16. Rusty, are you doing it for the sake of the goal ... or doing it for the sake of the fun? Go power-caching for the numbers if the goal is important. Or not, if it ain't. But if we're out there for the fun, I say, go visit the fun ones and to heck with the numbers.
  17. Best reason is that WGS84 is the world standard ... and the basis of GPS. The British grids are available on Garmin units ... so are many other local datums. (Insert geodesy lesson here... ) WGS has the advantage of being a geocentric system - and the GPS system (the birds, not our little bugs) are calibrated for it and by it.
  18. I have two Garmins that have firmware for aviation ... but neither has WAAS. And I'm getting hungry for a WAAS unit. Only trouble, I'd rather not spend a whole lot of $$$. Magellan's Explorist 100 is listed as being a WAAS unit for a VERY reasonable price -- $99 at REI. The 200 is $149 ... and for $199, at Costco, I can get the Magellan SportTrak Color. These prices are tempting me to cross the G-M line. gpsinformation.net has some very persuasive things to say about the SportTrak Color ... but nothing, yet, about the Explorist series. Has anyone here had any experience with the Explorist series, out in the woods?
  19. I have two Garmins - GPS III Pilot (like III+ but with aviation database and functions) that I use for geocaching GPS 155 TSO (look it up) that I use for flying - full IFR installation in my Tri-Pacer Neither has WAAS ... I may trade in the III Pilot for a Garmin GPSMap 96.
  20. If you want to really nail down the coordinates of your cache, the Trimble units will get you down to the centimeter. That's what they are for. Do you really need that level of accuracy? GPSinformation.net tested the accuracy of a Magellan Sportrak Color and found that it was giving them 1.6 meters accuracy (that's 0.001 minute of lat/lon) in an area of moderate tree cover. AOPA Pilot (December 2004) alleged accuracy of 4 feet in tree cover for Garmin's GPSMap 96c - with WAAS turned off! That's enough for me, unless I am surveying - and I leave that to the professionals.
  21. This is from GEODESY FOR THE LAYMAN, Defense Mapping Agency Technical Report 80-003, December 1983: "A datum is defined as any numerical or geometrical quantity or set of such quantities which serve as a reference or base for other quantities. In geodesy two types of datums must be considered: a horizontal datum which forms the basis for the computations of horizontal control surveys in which the curvature of the earth is considered, and a vertical datum to which elevations are referred. In other words, the coordinates for points in specific geodetic surveys and triangulation networks are computed from certain initial quantities (datums)." Yeah, it's government-speak. But this usage goes back to the origins of geodesy.
  22. Aviation-grade GPS units do have that, or at least the top-of-the-line units do. It's called RAIM (Receiver Autonomous Integrity Monitoring); it's built into the box, and it determines whether there will be enough birds in the sky to navigate safely in bad weather. If you're flying in the slop, you need it.
×
×
  • Create New...