Changing from National Grid coordinates to local coords

Hi all,

I'll try to describe my question as best I can but please bear in mind:

My father in law is a civil engineer but works everything out on paper. I'm convinced there is a better way (using autocad). I'm competent with computers but never used autocad in my life and I'm not a civil engineer.

Before starting setting out on site, he is given the proposed layout, based on 'National Grid Co-ordinates' (in the UK).

Currently he's working on a carpark which is a nice grid but on a different axis to the national grid coords. To make things easier, he picks a coordinate and labels it Easting 100.000 & Northing 100.000. From there he converts the coordinates given to values relative to this 100,100 coordinate. He does this on paper.

Could this be done using AutoCad (2011)?

Any help is greatly appreciated. If anything is unclear I'll try to elaborate.

Cheers!

Hi,

I'm not entirely sure what your question is.... do you want to use the real National Grid co-ordinates or find a simpler way for him to place a grid on his car park drawing?

My father in law is a civil engineer but works everything out on paper.

I've worked with older guys like this before.

Before starting setting out on site, he is given the proposed layout, based on 'National Grid Co-ordinates' (in the UK).

 

Currently he's working on a carpark which is a nice grid but on a different axis to the national grid coords. To make things easier, he picks a coordinate and labels it Easting 100.000 & Northing 100.000. From there he converts the coordinates given to values relative to this 100,100 coordinate. He does this on paper.

 

Could this be done using AutoCad (2011)?

It could be done in AutoCad provided he has the proposed carpark layout and setout data in CAD format (e.g. an AutoCad .dwg file or something similar) and knows how to transform the data (which if he can do it on paper then he does).

It might just be easier for him to ask the surveyor or civil design engineer to send the setout coordinates for the car park on local site grid coordinates to him. It is even easier to do this in civil engineering and surveying software packages (and not just basic AutoCad).

This is extremely simple in AutoCAD, but even easier if you have a digital drawing.

First thing to do is find out the Local Scale Factor. based on the National Grid Easting.

Then remember the formula, Ground distance times Scale Factor equals map distance.

Then apply that scale factor to the supplied drawing. Move the whole drawing bodily to the chosen coordinates for the base point, rotate it all so that one line of the car park is nicely North, and there you are.

Of course, it may turn out to be more simple. If the new construction has been drawn using actual or "flat earth" lengths, then you will not have to take into account the Local Scale Factor.

Since using AutoCAD for these sort of projects, my calculator is gathering dust.

If a drawing is not available, then draw out the points using the National Grid coordinates and then rotate and translate to suit. Pick off the new coordinates.