28th June 2012, 08:53 PM
Wax Wrote:I repeat architects are not surveyors their remit is to design, someone else has to fit it together hence the problems that arise if they are asked to draw an existing structure. Much OS data is now captured using differential GPS with aerial photography. Some poor sod then ground checks it with a pad linked to GPS and plots in real time. Met an OS surveyor a month or so back and he was complaining that the programme was written so the surveyor on the ground could not use all the little ruses that they developed when plotting with a pencil and measuring with a tape. He said all the skill had been taken out of the job. He also showed me how using the GPS was high lighting all the little positional errors inherent in 1:2500 mapping.
What a lot of people do not think about is that a map is not a drawing of a flat surface it is a depiction of the curved surface of the earth plotted in two dimensions Grids such as the OS national grid were developed to factor this in and there are a variety in use. If you are mapping over distances you need to factor in the mathematical corrections to bring the curved surface to the grid you are using. This can be around 10cm in 300 m. Corrections may also be needed if you are levelling over any distance. GPS usually asks you what grid you are using and does the corrections for you. it is these little details that archaeologist are often not aware of that make me suggest that archaeologists need to understand some basic principals. Transverse Mercator any one?
Hang on a minute 'curved surface of the earth', you mean it's not flat!! That's where I've been going wrong all these years! Seriously though, I would consider the level of surveying knowledge you've been explaining way above the requirements of most archaeologists. And certainly above most architects. If you understand all that, good for you. Can you now perhaps think of a few other things that archaeologists might use everyday that you don't understand in such detail and let me know so I don't feel quite so useless! Cheers.