16th February 2006, 02:21 PM
The biggest problems with both offsetting and triangulation are:
Topography - if you site is not flat, you get all sorts of distortion on the slope;
Calibration - tapes do stretch, so you have to keep them well calibrated and replace them when knackered; often not done in archaeological units (at least in the old days when I worked there);
Sagging - if the tape has to be held in the air, unsupported by the ground, you get more inaccuracy from sagging. You need to keep them stretched tight, but that can make it hard to hold the 0 end steady and also knackers the calibration.
Human error - extremely easy to get your right-angles wrong, plus a whole host of other easy mistakes to make in what is basically a simple process.
So, the basic lessons are:
- only use hand-measurement as your principal method over short distances, or to cross-check digital surveying for errors;
- make sure your equipment is in good condition;
- don't rush, and make sure the results are checked by the supervisor.
1man1desk
to let, fully furnished
Topography - if you site is not flat, you get all sorts of distortion on the slope;
Calibration - tapes do stretch, so you have to keep them well calibrated and replace them when knackered; often not done in archaeological units (at least in the old days when I worked there);
Sagging - if the tape has to be held in the air, unsupported by the ground, you get more inaccuracy from sagging. You need to keep them stretched tight, but that can make it hard to hold the 0 end steady and also knackers the calibration.
Human error - extremely easy to get your right-angles wrong, plus a whole host of other easy mistakes to make in what is basically a simple process.
So, the basic lessons are:
- only use hand-measurement as your principal method over short distances, or to cross-check digital surveying for errors;
- make sure your equipment is in good condition;
- don't rush, and make sure the results are checked by the supervisor.
1man1desk
to let, fully furnished