Tuesday, July 27, 2010

DWG to SHP - Data Interoperability / FME Workbench

In my previous post I discussed about the issues faced in CAD to GIS conversion when using basic utilities of ArcGIS. In this post I will discuss the route taken by me to convert a set of DWG files to SHP format.

If you are working with a data pertaining to a large area or data with a large number of layers Data Interoperability extension for ArcGIS becomes very essential. While Data Interoperability can handle nearly 100 data formats, FME Desktop on which Data Interoperability is based on can handle 300+ formats. Whatever conversion you need these software have an answer - cad to gis (shp, geodatabase, kml, 3d pdf etc.)

I was involved in a project containing CAD drawings spread across several files. This technically is known as data in tiled format. Though FME has facilities to work on tiled data I decided to take up another route. That is, I used AutoCAD to stitch together all the files. This enabled me to do a reality check on the data quality - arrangement of layer components. It came to light that layers were mixed up, which often is the case with CAD drawings. Working with AutoCAD enabled me to correct such anomalies and also reduce the number of layers. 

While the direct read feature of ArcGIS collectively depicts all the layers in the form of points, lines, polygons etc. an FME Workspace depicts all the layers as they are in AutoCAD as shown in figure below. Buildin.. and Compo.. seen in left are the two layers in AutoCAD which are known as reader feature types in FME terminology. Same feature types seen at right are the writer feature types, that are the output layers in shapefile format(in my case). The readers and writers are seen in a workspace as soon as our requirements are defined. 
Fig. FME Workspace
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