Changing coordinates of grid system

[Lrees]

Hi, hope the title explains roughly what I want to get done.

 

I work in construction and often have to look at the drawings in CAD so that I can pull dimenssion and information from it.

 

Out on site, we have a grid system to which everything is set out. But with some drawings, the grid does not match (scale is ok, but the X & Y values are diffirent).

 

How would i go about correctly orientating the drawing and saving changing it so the correct XY values show for each point?

 

I am using AutoCad 2009. Any help would be great.

 

Thanks

[chelsea1307]

How is the grid created in Autocad, are you talking about the grid that you can turn on and off that is a bunch of evenly spaced dots? Or is it a grid created using lines?

[Lrees]

its a grid using lines.

[chelsea1307]

So the information excluding the lines of the grid is correct right? And your only problem is the lines of the grid in autocad dont match the lines of the grid on the construction site

[Lrees]

let me try to explain better. I have a drwaing of a building. the scale of it is correct, but when i id say the corner of the building on CAD it gives me the coordinates in national grid (ordnance survey). But out on site, I am working in Local grid.

 

What I would like to do is manipulate the cad drawing so that when I id a point on CAD it gives me the coordinates in the local grid that I am using on site.

 

Bit awkward for me to explaing, but hope that explains it a bit.

[chelsea1307]

In that case I am unable to help, but im sure someone with experience in what your trying to do will come along shortly and explain how to do it

[Lrees]

Ok, thanks for you time though.

[eldon]

the coordinates in national grid (ordnance survey)

 

I hope that you are using a local scale factor to get back to actual distances

 

But if you are using the flat earth system, either set up a User Coordinate System (UCS) or move and rotate the whole drawing until it is on the site grid coordinates. (Always keep a copy of the original drawing to refer back to)

[ScribbleJ]

Are you trying to go from an assumed coordinate system (and I think you are b/c architects and structural engineers don't use state plane coordinates) to a state plane projection coordinate system? If so then you will need to have a known point for both to move the drawing to the system you want to use. If you don't have a know point it will be nearly impossible to get the file drawing you want to the coordinate system your using.

[Lrees]

Are you trying to go from an assumed coordinate system (and I think you are b/c architects and structural engineers don't use state plane coordinates) to a state plane projection coordinate system? If so then you will need to have a known point for both to move the drawing to the system you want to use. If you don't have a know point it will be nearly impossible to get the file drawing you want to the coordinate system your using.

 

 

yes, that pretty much sums it up. And yes I have many points on the drawing that I know the coordinates for (or know what I want them to be)

[eldon]

The trouble with a lot of large projects is that the designers put national grid coordinates on it without realizing that 100metres on the drawing is not that distance on the ground.

 

It is easy to find out what the Local Scale Factor is for the site, then you should scale the design drawing so that you get true ground distances. Then you can move and rotate the whole site to suit your local grid. Then you can take off coordinates.

[Lrees]

The trouble with a lot of large projects is that the designers put national grid coordinates on it without realizing that 100metres on the drawing is not that distance on the ground.

 

It is easy to find out what the Local Scale Factor is for the site, then you should scale the design drawing so that you get true ground distances. Then you can move and rotate the whole site to suit your local grid. Then you can take off coordinates.

 

 

That is not my problem, I use a total station (EDM) for setting out, which relies on me putting coordinates in to set everything out. Everything on the drwaing usually has a dimmension of grid lines (say 1m off grid line A, where i know that grid line A has a value of 900, so i then use 901.

 

What I want to do is match the drawing on CAD xy coordinates with what I am using on site.

[eldon]

Pick a point where two grid lines intersect, and you know the coordinates in local grid. Then move the whole drawing so that intersection is at the correct coordinate. Then rotate everything about that point, so that the grid lines are properly aligned.

[Lrees]

yes thats what I would like to do, but don't know how.

[eldon]

But I told you how. Just use the commands MOVE and ROTATE, coupled with Osnaps for pin-point precision.

 

If the drawing units are millimetres, and your total station prefers metre units, then you must scale by 0.001.

[Lrees]

great thanks, didn't knwo the commands.

 

Will try now!

[Lrees]

Thanks for that. managed to get it moved. i just id a point and then worked out this diffirence from current xy coordinates on the drawing to where i wanted it to be, and moved it by that ammount.

 

Thanks for your reply.

[eldon]

You very rarely have to work out the relative difference in AutoCAD. There are ways to show it what you want. In this instance you could have entered MOVE, then choose ALL, then for the base point you pick the intersection, and for the second point of displacement you could have typed the required coordinates x,y.

 

When you have had a bit more practice, you could explore the ALIGN command.