Georeferencing is the process of spatially adjusting a CAD drawing without actually changing the original source data. In ArcGIS Pro, this is performed by linking points in the CAD drawing to known geographic coordinates. Once you have georeferenced a CAD dataset, it will be transformed on the fly in memory while the source data remains unchanged on disk.
Limitations of CAD datasets
DGN and DWG formats do not natively support the ArcGIS georeferencing system. To get around this limitation, ArcGIS Pro extends the properties of a CAD dataset to include georeferencing control points as ancillary information. This information is defined as from-to coordinates and is stored in an auxiliary world (.wld) file.
Georeferencing a CAD dataset is limited to a two-point transformation using the similarity transformation method. This adjustment method maintains the aspect ratio of the CAD drawing and prevents skewing to the x- and y- axes. The purpose for georeferencing a CAD dataset is to accurately overlay the CAD drawing with existing spatial data without skewing its geometry. If a more complex transformation is needed, you can load the data into a geodatabase and use the Modify Features pane.
Control points
Control points define the displacement paths known as links and form the basis of georeferencing. A maximum of two links are possible with CAD datasets. A one-point transformation comprises one link and moves the dataset. A two-point transformation comprises two links and moves, rotates, and scales the dataset uniformly.
You can create control points manually with the pointer by clicking in a from-to direction, load them from a world file, or add their coordinate information to the Control Point Table.
World files
World files are saved with the file extension .wld. Using a world file to store control points is the best practice for sharing and reusing links in other projects and map documents. ArcGIS Pro uses the file name and its location to link the world file to a particular CAD dataset.
To associate a world file with a CAD dataset, the following criteria must be met:
- The world file and the CAD drawing must have the same name (prefix). For example MyDrawing.dwg and MyDrawing.wld.
- The world file must exist in the same folder as the CAD drawing.
When these two conditions are met, the world file becomes hidden from the Catalog pane. ArcGIS Pro loads the control points into memory and repositions the CAD dataset automatically when that dataset is added to a map.
Universal world files
A universal world file defines control points for all CAD datasets that are stored in the same folder and have not been georeferenced.
To define a universal world file, the following criteria must be met:
- The world file must be named esri_cad.wld.
- The world file must exist in the same folder as the CAD drawing.