A world file (WLD3) is a text file containing four points that describe a coordinate transformation. The points are used to calculate two vectors that define the offset, scale, and rotation of coordinates within the assigned spatial reference. The transformation information is only valid with the matching spatial reference file (PRJ) for which it was created. The best CAD, BIM, and GIS workflows attempt to avoid the need for a world file by using geospatial coordinates within the CAD and BIM files themselves.
The information in a world file is comprised of two sets of points. The first row defines a displacement vector with a set of from and to points using the following syntax: <from-pt1x,from-pt1y,from-pt1z> <space> <to-pt1x,to-pt1y,to-pt1z>. The second row defines a second displacement vector and another set of from and to points with the following syntax: <from-pt2x,from-pt2y,from-pt2z> <space> <to-pt2x,to-pt2y,to-pt2z>. The resulting two vectors define how two points within the CAD or BIM model's coordinate space should be offset, scaled, and rotated within the map. The two sets of points may be directly related to the model and map coordinates as in the case of adding control points when georeferencing, or the coordinates may be simplified to mathematically define the necessary transformation. The resulting transformation is a 2D affine transformation with a z-coordinate offset that is applied to the entire dataset.
The data looks similar to the following:
25933.063000,9032.704720,1702332.110159, 309622.102491,-8987.532001,1300.050854 32047.556994,13057.483520,1706354.400361 303697.073028,-9091.566340,1337.519601
It is not uncommon for BIM or CAD design files to use a relative or local coordinate system rather than a geospatial coordinate system within a model. In such cases, ArcGIS Pro requires an offset file (WLD3) to properly position your BIM data or CAD data. Because a world file is based on a specific coordinate system definition (PRJ file), you first must define a spatial reference for the CAD or BIM data; either select one from the CAD or BIM File Properties dialog box, or use the Define Projection geoprocessing tool. Spatial offset information defines the offset from a known geospatial coordinate system defined in an existing PRJ file and the coordinates of your BIM data. A WLD3 file needs a matching PRJ file. The spatial offset information created by ArcGIS Pro georeferencing tools is stored in a WLD3 file with the same name as the BIM file. If the coordinates of the BIM model are based on the coordinates of an included PRJ file, there is no need to define a spatial offset using a WLD3 file and the georeferencing tools in ArcGIS Pro. In such cases, specifying the correct PRJ file that matches the coordinates of the geometry is sufficient to define the data's correct geospatial position.
Standard Esri world files for CAD and BIM data are saved with the file extension .wld3. Once defined, the world file will properly adjust the CAD or BIM data in any map or scene as long as the corresponding PRJ and WLD3 files are present in the same file folder as the source data.
For ArcGIS Pro to recognize a world file for a CAD dataset or BIM file, the following criteria must be met:
- The world file and the BIM or CAD design file must have the same name (prefix), for example, MyDrawing.RVT and MyDrawing.wld3.
- The world file must exist in the same file folder as the matching BIM or CAD design file.
Universal world file (ESRI_CAD.wld3)
The universal world file is a means for defining a single spatial transformation offset for a folder of CAD and BIM files that have the correct positioning relative to one another and a single Esri spatial reference definition (PRJ), but need to be repositioned. The universal world file defines the offset parameters for all BIM or CAD files that are stored in the same file folder and that do not already have a WLD3 file name that matches the BIM or CAD file name.
For ArcGIS Pro to recognize a universal world file, the following criteria must be met:
- An Esri coordinate system upon which the world file is based must exist for the CAD or BIM data.
- The world file must be named ESRI_CAD.wld3.
- The world file must exist in the same folder as the CAD or BIM design files.
- No specifically named WLD or WLD3 file exists in the same file folder as the data.
Legacy CAD 2D world files
ArcGIS Pro also supports 2D world files valid for 2D CAD drawings. The format of the 2D world file is the same as the 3D world files except the two sets of coordinates are 2D points and the file has a .wld file extension. When there are both a WLD and WLD3 file present the WLD3 file will be used in ArcGIS Pro. ArcMap will only use a WLD file.