I have a lot of DWG files like the base map, and water and wastewater network.
I am looking for the principal steps to import my files into my QGIS project.
You can convert the DWG files to DXF (which QGIS does support) using the Teigha® File Converter.
It’s a free (not open source, unfortunately) cross-platform application provided by the ODA to end users only for the conversion of .dwg and .dxf files to/from different versions.
It depends on what you mean with import. Import data to actually do something with it, or just to have a background layer for viewing.
Also, consider this: In GIS, basic building blocks are points, lines, and polygons (sometimes called basic topological types), and inside CAD, you are working with drawings which can be made of anything, including objects that can’t be converted into any of before mentioned types. These would include more ‘exotic’ types of geometries like curves, solids, etc, also blocks (or block references), external raster references,…
ArcGIS for example does a pretty good job of displaying (and even allows limited editing) of DWG/DXF files, while other GIS software packages attempt to simply import the data as best they can, because the contents of a dwg file can be too complex to have a tool that would simply translate CAD ->, GIS.
I often receive cad files but I don’t have AutoCAD, so I break them down with DoubleCAD XT which is a free download. I export each layer or set of data by selecting it then SAVE AS (toggle the selected option) type = DXF-2004-2006. These seem to import fine into QGIS, when you open it up as a vector layer. FME server might be worth a try as well, vectors – save as dxf, then resave in DoubleCAD to a dwg. You cannot keep the attributes so you have to work with one feature of data at a time. there is a free online tool for converting dxf and dwg to shapefile and kml here: , but I did not test it in lack of a dwg Open Source gvSIG is said to capable of opening DWGs. From there, it should be possible to export to shapefiles. Not tested here I’m afraid.
As many have said open source software can not support dwg. Dxf, however, is supported and Autodesk provides a cloud tool that you can use to convert dwg to dxf: autocad 360 (or the previous version AutoCAD ws). The advantage of this tool over many others is that it supports all versions of dwg, also the most recent ones. DWG is a proprietary, closed format. As many would be able to confirm is one of the less interoperable formats. Long story short: it is not possible to open a DWG file with an Open Source software/library.
There are/were attempts to create an OS library to read dwg but afaik they do not work very well. If there is software other than Autodesk that can open DWGs then it uses a non-open source library to do that, for this reason, you will not see DWG support in QGIS. As already suggested ask to have the DWGs saved as DXF (that is somehow more interoperable) or as shapefiles (Autocad map can do that).
Your easiest option is: http://www.guthcad.com.au/cad2shape.htm It is not free, but the company is specialized to convert cad dxf/dwg files to shape.