I’ve been struggling with being able to overlay PDFs from our drawing sets within Emlid Flow, but recently had a break through and wanted to share incase it would benefit anyone else. I’m still very green with all of this, so please let me know if there are any glaring issues or bad practices here.
As a GC, having our Orthophotos overlaid with the site plan and structural details has been a huge help in just double checking and looking for busts. Not sure this would help the surveyors out there, but for any GCs…
Prerequisites:
- Vector based PDF.
- Adobe Illustrator - I’m using 2025 in this example.
- QGIS - Again, I’m using version 3.34.
- A base CAD file that references a known CRS.
- Import PDF to Illustrator.
- “Print as PDF” or export the single page in question. Don’t try to do multiple pages as once. In Illustrator, open the PDF directly.
- It may ask you “To preserve appearance, some text has been outlined.”, click yes. It will then ask if you want to keep it as a RGB, say yes again.
- Once loaded, you can delete some of the layers that may have information you don’t need overlayed. In this example, I don’t want the footing tables in Flow, so I will remove the layers. You can also clean up anything else that you do not want included.
- Once it is cleaned up to your liking, it is time to export it.
- File > Export > Export As > Then change the file type to “Autodesk RealDWG.DXF”
- There are two “Autodesk RealDWG” types, do not select the .DWG one.
- Next, open QGIS. For this example, I am using version 3.34.
- I am also using the “DXF Import/Convert” plugin that you will need to download.
- You’ll need to import your base CAD file that is setup on the CRS of your liking. Ensure that QGIS is using the CRS that matches your CAD File. When “georeferencing” my PDF file, I set control points based on the CAD file, not known coordinates. If you know the actual coordinates of your PDF, this might not be required, but it will be a check that everything is aligned correctly as well.
- Go to Project > Import/Export > Import Layers from DWG/DXF
- If you are importing a DXF, be sure to change the file type in the bottom right corner.
- The import window will then open, double check the CRS is correct and then click “Import” in the top right. This process could take a few minutes. Once completed, click “Ok”.
- Add a background map.
- I also like to add a background map as well, if you would like to do the same:
- Web > Quickmap Services > OSM > OSM Standard
- You can then right-click on your layer in the bottom left and click “Zoom to Group”
- You should now see your base CAD file on top of the base map.
- Georeferencing your PDF.
- Now the fun begins. Make sure you have the “DXF Import/Convert” plugin installed. Go to Vector > DXF Import/Convert > Import or Convert
- Click “Browse” in the top right and select the DXF file that we exported from Illustrator forever ago.
-
Georeferencing your PDF continued…
- Once loaded, click “Import” in the bottom left, no need to make any other changes.
- You will need to rearrange your new layer, as it is likely “under” your base map.
- Click on your base layer and drag it below the layer you just imported. If you right click on the new layer and “Zoom to Group” it is likely out in the ocean or in a mountain, depending on where you are.
- Georeferencing your PDF continued…
- You will now need to expand your (L) layer, and right-click.
- Export > Save Features As
- You will now need to expand your (L) layer, and right-click.
- Georeferencing your PDF continued…
- Change the Format to “GeoPackage”, you may need to scroll up.
- Set the output filename that whatever you wish.
- Under “Field to Export” select “Deselect All”
- Reselect the following:
- Layer
- Line Type
- Size
- Size_U
- Color
- You can click “OK”.
- Reselect the following:
- Next, right-click on the top level group of the layer your just exported and remove it. This should leave just your base map and base CAD file.
- The go to Layer > Georeferencer.
- When the new window pops up, click “Open Vector” and select the file you just exported. You should now see your cleaned up PDF in the Georeferencer window.
- Georeferencing your PDF continued…
- Next, zoom in and select a point of your PDF that you can translate to your base CAD file. Look for a defined building corner, center of column, benchmark, etc etc.
- Select “From Map Canvas” and then select the same point from your base CAD file. Zoom in as far as possible to help with the accuracy.
- After you select a point on the Map Canvas, it will take you back to the “Enter Map Coordinates” pop-up. Select OK.
-
Georeferencing your PDF continued…
- Repeat this at MINIMUM three times.
- Once done, you should have at least three ground control points shown.
- Georeferencing your PDF continued…
- Once done setting GCP’s, click the green arrow or “play button” in the toolbar. It will prompt you to set the output filename and open another window.
- Click Ok, the window will close, and you can click the green button again. Your new layer will now be created.
- Your PDF will now be overlaid with your base CAD file and base map. Double check the alignment and that everything looks correct.
- Georeferencing your PDF continued…
- Now, find the new layer you just added (you can toggle visibility to help find it if needed) and then once again, right click it, and go to Export > Save Features As.
- Change the Format to “Autocad DXF” and set whatever filename you would like. Click Ok.
- Import to Emlid Flow
- You can now import the file you just saved as “DXF as CAD Drawing” in Flow.
You should now have your PDF file correctly displayed on top of your Flow project.
Next on the list is to figure out how to host a WMS/WMTS server locally and get out of being on a paid MapBox plan for the map layers (Orthophoto background).