Monday, December 1, 2008

AutoCAD Map 3D: Rubber Sheeting a Drawing with No Coordinate System

What happens when you get a drawing file with no coordinate system and you need to align it to your existing map? This is where the Rubber Sheet command comes in handy.

Rubber sheeting is a nonuniform adjustment of a data set based on the movement of known control points to new locations. For example, data collected by aerial survey may be inaccurate because of flight alignment and camera inaccuracies. By comparing this data with accurate ground survey data, the aerial data can be stretched or rubber sheeted over the accurate data using control points and monuments common to both data sets.

Use rubber sheeting when you want two or more different data sets from different sources to align geographically: for example, when stretching a new subdivision map into a preexisting parcel map.

The reference map is correct, but the map with new details is severely distorted. By running the Rubber Sheeting command and selecting common control points, the two maps can be correctly aligned.

Objects that have a given shape, such as circles, arcs, and ellipses, retain their original shape.

Warning: Use rubber sheeting only when absolutely necessary because it can severely compromise the accuracy of your data.

Because rubber sheeting is not a linear transformation, it is difficult to reverse the effects of the transformation and return a drawing to its original state. You should save your drawing before you perform a rubber sheeting operation.