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To make topography from drone photos, fly the site and take overlapping pictures, process them into a 3D terrain with photogrammetry software like Autodesk ReCap Photo, export the terrain, slice it into contour lines (here in 3ds Max), and export the contours to DWG for AutoCAD or Revit.
What do you need for drone topography?
| What | Used for |
|---|---|
| A small camera drone | Taking the overlapping photos |
| Photogrammetry software (ReCap Photo here) | Turning photos into a 3D terrain |
| 3ds Max | Slicing the terrain into contour lines |
| AutoCAD or Revit | Using the topography in your drawings |
I use a drone to make topography for my projects quite often: for site studies, rough earthwork volume estimates and so on. The DJI Spark and DJI Mini 2 were the small-drone examples in the original version of this guide.
If you are comparing equipment now, the Potensic ATOM 2 Standard Kit is a newer option to consider. This gray kit includes the RC PTD 1 display controller and one battery. The camera supports timed still photos and can point straight down. Check the exact package and your flight-planning requirements before buying; this is not a claim of tested ReCap compatibility or survey-grade accuracy.
Besides the drone, you need Autodesk ReCap Photo, Autodesk 3ds Max, and either AutoCAD or Revit. If you need several of them, buying them as a suite can save some money.
Steps
- Taking the pictures
- Processing the pictures in ReCap Photo
- Turning the terrain into contour lines in 3ds Max
How do you take drone pictures for mapping?
If you’re new to flying, practice with the drone before you take it to a job site. Set the camera to its best picture quality.
Make the pictures overlap by about 30% on each side (see picture #1).
For more terrain detail, don’t fly too high. But when you fly low, watch out for trees and utility poles, and fly over them, not around them. Trust me, I learned this one the hard way.
How do you turn drone photos into a 3D terrain?
Next, upload the pictures to ReCap Photo, Autodesk’s photogrammetry service (it started out a few years ago under the name Memento).
Once the pictures are in the Autodesk cloud, delete any you don’t need before you submit them for processing. Processing can be quick, but the servers are often busy, and it can take a few hours depending on how many people are in line.
When it’s done, the terrain shows up on your desktop and looks something like this:
Orbit with the view cube in the top right corner and you’ll see the actual 3D shape of the ground and everything on it. This is a beach site of mine in Panama:
The model comes out at real-world scale automatically because ReCap uses the GPS locations the drone saves in each photo. You don’t have to scale anything.
If there are trees on the site, cut them out with the ReCap Photo tools and patch the holes with the automatic Fill Holes tool. If you leave the trees in, they’ll mess up the contour lines later. (And no, you don’t need a city permit to remove trees in ReCap Photo.)
When the terrain looks good, export it to your drive as an .fbx file. During export you can reduce the triangulation of the surface. I usually reduce it by 30% to 50%, and through trial and error I’ve found that even a 70% to 80% reduction works fine in most cases. You don’t need maximum detail, and a lighter mesh is much faster to work with. Try a few settings to see what your computer handles without losing contour quality.
Click Export and the file should be ready in a few minutes.
How do you make contour lines from the terrain?
You now have a 3D shell of the terrain saved as an .fbx file. Open 3ds Max and drag the .fbx into the Perspective viewport:
That’s it, the terrain is in 3ds Max. Since both programs come from Autodesk, there are no compatibility problems. I like to center the model on the axes and move it just above zero.
Make the first section
Find the Section tool in the panel on the right and click it.
In the Perspective view, click in the middle of the terrain and drag outward past its edge, then let go. Your first section is in place:
Make sure the section covers the whole terrain.
Tip: press Alt+W with the mouse over a viewport to maximize it. Press Alt+W again to go back to all four.
Move the section
Use Select and Move (shortcut W):
Drag the yellow XY square to move it freely, or drag the X or Y arrow to move it in one direction only.
Resize the section
If the section isn’t big enough, use Select and Uniform Scale the same way: drag the arrows or the yellow triangle in the middle.
Draw a rectangle for the section
Now draw a rectangle on the section. It will cut through the terrain where we want the contour.
- Set snap to 2.5:
- Right-click the 2.5 snap icon to open Grid and Snap Settings and make sure Vertex is checked:
- In the panel on the right, pick Rectangle:
- Click an outside corner of the terrain and drag to draw the rectangle:
- Set snap to 3:
- Snap the rectangle to the lowest point of the terrain:
- Move the rectangle so it covers the whole terrain:
- Before going further, check your units in Customize > Units Setup. If the units are wrong here, your contour spacing will be wrong too.
Array the sections to make contour layers
- Select both the section and the rectangle, then go to Tools > Array:
- In the Array dialog, turn on Preview and set the distance between layers (your contour interval) and the number of layers:
Click OK. Switch to Wireframe and you’ll see the contour layers in yellow on the terrain:
- Select the bottom section, go to the Modify tab and click Create Shape. Then press Delete to remove that section. Repeat for each section.
The contour lines are done:
Export to DWG
- Hide or delete the rectangles (magenta above). Select all the contour lines and go to File > Export. Choose .dwg as the file type:
In the export options:
- Pick your CAD version.
- Check Selected Objects.
- Check Skip Hidden Objects.
Click OK.
Open the DWG in AutoCAD, or import it into Revit, and you have real topography from your own site.
How accurate is drone topography?
Good enough for site studies, concept design and rough earthwork volumes, which is what this method is for. It’s not a survey. Consumer drones locate photos with regular GPS, which can be off by several feet, and photogrammetry also picks up grass, cars and anything else on the ground. For accurate elevations, surveyors use ground control points measured with survey equipment, or a licensed surveyor does the topo. If the topography will be used for construction, grading or property lines, get a survey.
Do you need a license to fly a drone for work?
In the US, flying a drone for work falls under the FAA’s Part 107 rules (14 CFR Part 107). The main points from the FAA’s Part 107 page:
- Remote Pilot Certificate (§107.12). You pass the FAA knowledge test to get it. You must be at least 16.
- Register the drone. It costs $5 and lasts 3 years, and most registered drones must broadcast Remote ID.
- Stay at or below 400 feet above ground (§107.51), unless you’re within 400 feet of a structure.
- Keep it in sight (§107.31). You need to see the drone with your own eyes the whole flight.
- Airspace (§107.41). Near many airports you need an authorization first.
- Flying over people (§107.39) is only allowed under specific conditions.
Rules change, so check the FAA site before you fly. Outside the US, local rules apply (my Panama example is outside the US).
What to do when it doesn’t work
- ReCap can’t stitch the photos. Not enough overlap, or blurry photos. Fly again with more overlap and steady, sharp pictures.
- The terrain has spikes or holes. Trees, poles and water confuse photogrammetry. Cut them out and use Fill Holes.
- The contours are at the wrong spacing. Check the units in 3ds Max (step 8) and the array distance.
- The DWG is empty or has extra lines. Make sure only the contour shapes are selected and hidden objects are skipped on export.
- The file is too heavy. Reduce the triangulation more when exporting from ReCap.
Once you have contours in DWG, you can use them in Revit for a site model. For textures on the finished site, see my free seamless textures.
The drone I used is on my My Toolbox page, along with the other gear I take on site surveys. If you turn the survey into a model, start with creating grid lines in Revit.
