I have some data that was recorded by our team in the field in Trimble TerraFlex. I've been able to export that data to Shapefiles and imported them in QGIS (2.18.0) in WGS 84 (4326) and are spatially correct when I pull in a Google Satellite Image through Openlayers WGS 84/Pseudo Mercator (3857).
What I'm trying to twofold:
A) Convert this data to a properly scaled DXF.
B) Get areas of the polygon layers and lengths of the line layers.
If I just export the data as is, it comes into AutoCAD at a really small scale (like any sort of area or length measurement starts with 0.000xxx). My understanding after doing a fair amount of research is that this is due to the data being in a GCS rather than a PCS. QGIS is trying to export using DMS instead of meters and is giving me really tiny numbers.
So, I need to reproject to a PCS, correct? The area in question is just south of Branson, Missouri and thus is in UTM 15N. If I change the layer CRS to this, the data moves on screen even if I have "On the Fly Transformation" selected and I can no longer use the Google Satellite imagery to spot check my locations. This is okay.
Unfortunately, when I export these layers to DXF with this UTM 15N PCS, the scale is still really, really tiny. Does anyone see any glaring issues with my process or know how to troubleshoot this? It's frustrating because I've done a good deal of work trying to understand how projections work but I still can't solve what seems like a relatively simple problem.
I can upload my project to a host and let someone work with it if that would help.
Best Answer
You are correct. AutoCAD expects metric units (though if you give it meters when it is expecting mm or vice versa you can get strangely large of strangely small measurements - see here). Giving it a dataset that is in a GCS (WGS84 in your case) just compounds the confusion as you rightly surmise (decimal degrees do not readily convert to metric units as it depends where on the globe you are).
If you are still getting really small measurements check two things: Firstly, have you exported the data with the correct projection? Don't change its CRS in QGIS on opening the layer but specify the CRS you want when you
Save As. Secondly check (using the link above for more information) that AutoCAD is set correctly to meters and not mm.