Surveying elongated features

[Edu]

Hi everyone,

this is just a simple question about the setting up the flight path when you are surveying elongated fetaures like roads or breakwater for example. Normally I tend to set up the flight path perpendicular to the axis of the featured, something like that:

but sometimes it is faster to do it this other way, running the drone along the structure:

I have never created a 3D model using the second set up. Is there any difference in doing that one way or the other when it comes to results in the 3D model output and accuracy?

thanks very much!

 

[Bigriver]

If you are shooting nadir, or straight down, and as long as you are getting similar side/frontal overlap, I do not think that there would be a difference in your model output or accuracy.

I fly missions both ways, but which method I chose depends on what I am mapping. If mapping a linear project that has no traffic, like your rock dike, a crossing pattern may be useful. Especially if it requires multiple batteries. You can walk along the route, land and change batteries when necessary, and re-launch to continue your mapping. I also think this method helps with lighting, as shadows do not have a chance to move much as you complete each section.

However for roadways, I try not to cross the roadway often. In that case, it is best to fly linear missions. On a long project, I will break it up into shorter missions, which helps me map an area in a shorter timeframe and reduce shadow changes. You can still walk along the long routes and swap batteries as necessary. Usually in 1/4 or 1/2 mile segments. (Of course you should also plan these missions to not fly over traffic linearly, and cross only when there is no traffic.)

If your mission requires a slightly oblique camera angle, you have other things to consider. On roadway projects, I often want to pick up and be able to read sign faces in the images. The linear mission is good for this. However on roadways with overhanging trees, having a camera angle that is angled under the trees provides more information. It is more difficult with linear missions, but you can program it to fly sideways to get the desired coverage.

As for speed, linear missions are usually much faster because of less turns.

 

[Edu]

Thanks very much Bigriver for your answer.

I normally do breakwaters and features along the coastline taking nadir pictures; some of those breakwaters are quite long and, in order to minimise the flight time, it is better to plan the mission witht he paths "along the structure" main axis. So you don´t have to use many batteries. It is good that, with a crossing pattern you can walk along as the mission goes by, but sometimes those structures are not full walkable.

I will have to survey more than 50 dikes like that one and I will give a try to both patterns.

thanks again for your help.