Transferring .DXF files to a GIS program

[Kat]

I am just learning QCAD professional. I am trying to draw precisely measured carparking spaces as polygons in QCAD and then overlay them on a street map that is created in GIS (using the QGIS software). I can't work out how to give the .DXF files a geolocation before I open them up in QGIS, so that they come into my street map at the right location. When I try to import the .dxf files from QCAD into QGIS their location and scale is way off my map and has no relation to it. The world coordinate system I am using in QGIS is EPSG:28355, as that suits my location in Australia. Can someone give me some step by step instructions please?

[andrew]

In what coordinate system (CRS) are you drawing the parking spaces in QCAD?

[Kat]

Hi and thanks for responding. I am not sure what coordinate system i am using. I am relying on the QCAD introduction book. I guess by looking at p.74 of the book that I have used absolute Cartesian coordinates. Attached is a screenshot of the different size carparking spaces (2.1m x 5.4m, 2.1 x 6m and 2.1m x 6.3m) I have drawn, if that helps.

[andrew]

I'd recommend to draw those parking spaces in a known CRS in QCAD. You can then specify that CRS when importing into QGIS. The CRS to use is the first thing you need to define.

Somehow, the software needs to know where in the world these features are located. The way to do this is usually by deciding what CRS is used and drawing the features in that CRS.

As DXF and DWG are CAD formats and unaware of the CRS in use, you might want to indicate the CRS in the file name for your own reference (e.g. mydrawing_EPSG_3857.dxf).