poor_PDOP

You would use a knife or chisel edge in the horizontal cut and measure from that point. Perhaps one of the surveyors has a picture showing the knife in use. This thread shows one way: Vertically Placed Disk Question I get it now. It is a vertically mounted plaque. Seems to be a laborious way to start/close a level flight, however I can understand the reason for the vertical mounting, i.e. longevity.

Hello DazDnFamily I'm also in the "geospatial industry" Interesting place for a Survey Mark and an interesting Survey Mark to boot, i.e. lots of information on the plaque and the fine is greater too. What I don't understand is how do you level from it, i.e. there is no nipple. The building looks very Gothic, you could almost think it was somewhere in Russia or Germany.

Well we have moved from Trigs to flowers, well heres my two bobs worth. Here is a georeferenced photo from my Garmin Oregon 550 while chasing down a geocache. The flower is from a Eucalypt. One of many in the park that are flowing in the hot weather this time of year.

Apologies, I need to correct myself. My quote "I also thought NAD27 was a transformation of WGS84" is not correct. NAD27 is a model to best fit for the North American Continent post 1927. When a world datum was required due to the role of GPS around the world, a new model NAD83, was adopted to fit as close to WGS84 (GPS Datum) as possible. source:-North American Datum Apologies again, I may have jumped onto this thread prematurely and may have missed a point or two. GPS is a multi headed animal bound to give the operator a false sense of security, i.e. clock errors, multipath, datum variables, SV geometry, etc

Front Range area, up north of Denver. Our N/S on NAD27 produces tiny errors (0.001 ~ 0.002). It clobbers us the other way. As an example of one of my caches over here - which are in the same general area as the caches I was mentioning in the earlier posts: GC1B035 NAD27 N 40°12.198 W 105°04.030 WGS84 N 40° 12.197 (almost no diff) W 105° 04.065 (whopping big diff!) Interesting that you compare NAD27 with WGS84! Remember that these datums are a snap shot of time, i.e. the 27 in NAD27 is a mathimatical model taken for 1927 and I think you'll find it is superceded. WGS84 is 1984. I also thought NAD27 was a transformation of WGS84, i.e a 2D mathimatical model transformed from a 3D model. If you input Northings & Eastings (NAD27) and the setting of your GPS displayed as Lats & Longs (WGS84) there may be a transformation difference, however I doubt it. The error should be within HHGPS accuracy. Anyway, food for thought.

I've been trawling this tread and find it hard to believe people would have two GPS units to tell them to go from A to B. Unless the person is a Taxi driver, Courier or a tradie I can't see the point in having two models. The Oregons are multi purpose, thus sacrificing some functionality to be all-rounders, i.e replacing nagging for beeps. Anyway, each to there own.

mmmmm. At first it seemed like a difference between decimal minutes and decimal degrees to me. You are dealing with Lats & Longs. Geodetic co-ordinates native to GPS datum. The Lats & Longs represent the imaginary lines of the mathematical model of the Earth, and are curved lines on a 2d map. In your case you have mixed up the the decimal point. Decemal Degrees are in the form n33.36662 whereas decimal minutes are n33.36.664. This is the cause of your difference. GC deals with decimal minutes. If my maths is correct, DecDeg=Deg+Min/60+Sec/3600 (I will stand corrected) I personally don't use Lats & Longs and just deal with 2D projections, but that is another story. HOWEVER, having said that, and reviewing you post before I reply; It may seem that your are entering what you require. (I can't remeber what 0.00001 decimal minute of arc is in metres). Your have to take into account that GPS is a dynamic system and this form of GPSr has accuracies of +/-3m (10ft) at the best of GPS sites. Don't expect absolute positioning here, there are two many variables to deal with. Answers to your questions 1. because the system is always moving. 2. Not if the values are small differences. Hope this is of some help.

Loved the pic of Survey Mark of Mason-Dixon Line. Mason-Dixon = history of surveying in the USA. I thought I'd add my 2 bobs worth. Here a pic of Little Dick Trig and Fire Tower. (Taken quite a few years ago.) Bruthen, Victoria. Australia

All I want is the ellipsoidal elevation derived from the GPS observations. I can apply the corrections myself. Is a GPSr able to show that ellipsoidal elevation value on the screen? People who fly may require altimeters to determine height above ground. You have to be carefull when talking about Geoids & Ellipsiods. The seperations can be quite large on some continents. And there is the added difference that some geoids models will differ from the Reduced levelling adjustment models (usually within a hand held GPSr accuracy), i.e. values shown on Govt survey mark databases.

Hello DF I have just purchased an O550, which is a O300 with more bells and whistles. You may have to calibrate the 2 axis compass (which means you have to treat it like a conventonal compass). The compass bearings can be set to three diferent modes, True, Magnetic and Grid. I personally set mine to grid because I have my unit set to UTM and not Geodetic co-ords, i.e Lats & Longs. Be carefull using Magnetic. An issue called Magnetic Declanation can be upto 11° (in my neck of the woods). Best stick to using True if you are using Lats & Longs. As for GPS accuracy; You have to remember that you are dealing with a dinamic system, i.e. you are moving, the SVs (Space vehicles) are moving , The earth is moving. If you are in a poor GPS location, i.e. poor veiw of the sky or it is a time of the day for poor SV geometry, then expect poor accuracy for your position. There is a function on the Oregons whererby you can view the "GPS Accuracy". I always refer to this when I am pinning down a cache, for it gives me a cynicism for the reading I'm getting. Hope this is of some help.