Effects of grid and ground coordinates on site
This might sound amateurish but I am a surveyor new to the field and new to this site and i’m hoping someone can clear something up for me…
I work in the uk and I cant quite wrap my head around the grid v ground debate. I understand the differences between the two and why they are both required for map projections etc. but i’m struggling to understand which is the best to use.
I know it depends on the size of the site but we often require our surveys to be based on OSTN15 coordinates (the UK coord system), so I tend to use a GPS rover in a lot of surveys and find doing everything on grid (with a scale factor) is much simpler, when using GPS. unless it is a small site and use only a total station where i will use a SF1. We also state that its been provided as grid coordinates and the scale factor so there is no confusion.
However (for example), if a house was drawn to be 10m long on plan (based on my grid survey) and then it was built on site to measure 10m long with a tape, if I was to resurvey the house, would it be exactly the correct size? (hypothetically, minus building tolerances and without setting it out, etc etc)
Or if everything was based on a grid with a SF, and then structures were to be set out by a surveyor on grid and then measured with a tape, would the distances/locations be different? If so, surely some sites surveyed and provided on grid are actually bigger or smaller than what they appear to be?
We have a large survey for a proposed pipe route coming up about 10k long, now i know we need to take in to consideration the curvature of the earth for this, but how would this affect the amount of pipe required? if that makes sense? will a survey in grid taking into account the curvature of the earth provide the correct amount of pipe or will it be more/less than if i were to use a SF1?
Also, when scaling factors are automatically applied when using GPS, where is the origin of the scale? i’m assuming its the zone origin? i.e N49 W2 as it is in the UK?
Apologies for the ignorance and the what some people may find, stupid questions, but I can’t find much online that puts it in layman’s terms or relates it specifically to topographical surveying/on site construction.
Thanks in advance!
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