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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.

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    Try reprojecting a shapefile from 4326 (lat lon wgs84) to 32615 (UTM 15N WGS84). Then try to export to dxf. To do this experiment load a single file in a new project choose the layer and right click and choose save as to correctly reproject the data – Gerardo Jimenez Nov 30 '16 at 15:48
  • Gerardo, this worked. I feel like it was the same thing I was already doing but apparently not. My only problem now is that the resulting measurements in AutoCAD are in meters. How would I go about changing this to feet without moving the features? – H. Rigsby Nov 30 '16 at 18:54
  • The major difference in your process was only having one layer open in a new project. Will this same process not work with multiple layers at once (that was what I was trying before)? – H. Rigsby Nov 30 '16 at 19:05
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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.

  • Mappa, thanks for this. Gerardo's solution above worked (I presume I was using the wrong "15N" CRS but I'm not entirely sure. As you seem knowledgeable in the scaling process, how would I go about getting my measurements in feet once in AutoCAD as opposed to meters. At the moment, the lines are at the correct scale in CAD but the length line item in the properties panel is in meters. I'm about to test and make sure that it comes in at the right location in a georeferenced drawing. – H. Rigsby Nov 30 '16 at 19:03
  • Update: Once I convert the DXF (accurate in meters) to DWG and XRef it into an established drawing of the property, the features show up still in meters (our company standard is to draw in "unitless" where 1 unit = 1 foot). So if I multiply the scale by 3.28084 the units are correct, but the insertion point is still way northwest of the rest of the linework. – H. Rigsby Nov 30 '16 at 19:16
  • UTM Crs define the measuring units for the east and north as meters. I think you should try with a state plane coordinate system aprppriate for your region, I am not familiar but check this: spatialreference.org/ref/?search=missouri. Main thing you will have to reprooject the original file in 4326 to the state plane one – Gerardo Jimenez Nov 30 '16 at 19:20

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