giovanni.mac

Defining projection of Shapefile and CAD

Discussion created by giovanni.mac on Sep 9, 2011
Latest reply on Sep 13, 2011 by giovanni.mac
Hi everyone,

I have a Shapefile that has been created from CAD file (using Surfer) with a local coordinate system.
Basically this local coordinate system has the same characteristics of the OSGB 1936 but it is defined in meters and the coordinates are shifted as follow:
the x coordinates are shifted by -500000
the y coordinates are shifted by -200000

For example:
In the local coordinate system I have:
x=124600 m
y=107400 m
whereas in the OSGB 1936 the same point will be:
x=624600 m
y=307400 m

When I import the shapefile into ArcGis of course it results that it doesn´t have a coordinate system.

Now what I want to do is:

1) shifting the shapefile so that it will result aligned with the OSGB 1936 System. I would like to perform this task with ArcGis (although I know how to do it with other software). Is it possible?

2) Attributing the OSGB 1936 projection to the Shapefile.
Now what I tried to do is shifting the original cad map in surfer so that it was perfectly aligned (as I said I would like to learn how to do this operation with ArcGis), then I exported the cad map as shapefile. The units were meters.
In ArcGis I then defined the projection of the Shapefile with the Define Projection tool but when I reopened the file I got this error message:
http://support.esri.com/en/knowledgebase/techarticles/detail/37732

Probably because my original CAD file was in meters while the OSGB 1936 System works in feet (is it right?).
How can I work around this problem? I found the help quite a bit confusing. I can see that my shapefile has unknown units but I don't know how to transform them such that they will result in feet, as the OSGB 1936 System.


I would really appreciate any help since I am really struggling with this urgent problem.

Thank you very much.

Giovanni

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