Mapping Failure

Failure to Resolve Shrubs and Trees

Three-Dimensional (3D) mapping with an aerial drone is exciting technology, but certain types of terrain will limit’s its usefulness. We’ll explain why some map jobs turn out good, others not so well.

Terrain Features that are Difficult to Resolve

In addition to our mapping service’s recommendation for photo set collection, we’ve found that terrain can be a significant limiting factor in the success of a mapping mission. Namely, shrubs and trees.

Many of our clients prefer terrain maps in the winter when the leaves are down so we can get ground-level elevation information. However, when the ground is covered with shrubs and trees the map doesn’t resolve very well. This is because the vegetation is too complex for the 3D processor. Remember, it’s trying to triangulate each pixel to assign its point in space. We’ve seen this even with overlaps as high as 90%/90%.

Notice the forested areas that don’t resolve well in this photo. You can see the trees have unfocused swirl artifacts. In more challenging areas, the map processor gives up and leaves the area blank. Although this picture came from our mapping service (which uses high-powered image processing), our panorama software PT Gui Pro also failed to resolve.

Other terrains such as developed properties have enough order to their colors, shades, and textures, that the map processor can triangulate the pixels. We’ve had excellent results mapping buildings, developed land, and roads.

What does our Mapping Service Recommend?

Our service includes these requirements for the photo set:

• Minimize areas with surface water

• Use an overlap of 75%/75% or better (we use 85 to 90%)

• Minimize windy conditions and long shadows

• Fly mapping missions at least 1.5 hours off solar noon

• The drone’s altitude should be at least 4 times the height of the tallest feature

However, they don’t have a specification for forested areas. We’ve talked about this, and they only go so far as to admit that these areas can be “challenging.”

Conclusion

We guarantee our map results and will not charge for results that our clients can’t use. However, mapping forested areas is risky for us so we may decline jobs like this. We’ll view your proposed map site with Google Maps and advise if it’s worthwhile to fly a mapping mission.



Leave a reply