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The 3 most common mistakes when planning the flight of a photogrammetric drone.

The use of drones in the field of cartography/topography has a number of advantages over traditional data capture systems.  In this article we are going to tell you about the 3 most common mistakes made when planning the flight of a drone. If you want to get a quality final result, keep reading to avoid them.

1. No overlap

This type of work requires both longitudinal and transverse overlap. Normally these values are around 60% – 80% on both axes. With these values you will obtain good results in works of flat orographies. However, if our drone does not have the capacity to maintain a progressive distance from the ground, you will have problems in more pronounced orographies, with the highest levels of overlap loss.  If you do not take this into account, you will be making one of the most common mistakes when planning the flight of a drone.

errores comunes al planificar el vuelo de un dron fotogramétrico

In this graph you can see represented the projection of the images (blue) with its corresponding overlap (yellow). As you can see, if you do not take into account the orography of the terrain and it is changing, our longitudinal overlap will be diminished or even null (in red).

These types of problems are often not detectable in the field due to the fact that the processes are usually carried out later in the office. In this image you can see the result of the lack of overlap once the images are processed. The resulting orthoimage has lack of information in the central part because that zone was the highest zone and had a lack of overlap. In order to solve this, the flight will probably have to be re-flighted, with all the costs that this entails.

Ortoimagen con falta de solape

2. Poor image quality

Another of the most common errors when planning the flight of a drone is the capture of images. You must consider that the camera/sensor has a series of parameters. So, if any of them is not properly configured for the type of images we intend to take, they will ruin our work and force us to have to repeat it.

We show you some of the parameters that can normally be configured in our cameras:

  • Diaphragm opening
  • Shutter speed
  • ISO
  • Focus
  • White balance

There is no exact setting for correct images in all situations. This is because there are other parameters such as flight speed, flight height or daylight. However, there are configurations that make images successful in 80% of flight situations.

Below we show you some examples of lack of quality in the images.

Blurred images

Imagen desenfocada de un vuelo fotogramétrico realizado con dron

There’s not much to talk about here. With a defocused image it will be impossible to have a high quality product. Something that is expected in a photogrammetric flight made with dron.

Imagen desenfocada de un vuelo fotogramétrico realizado con dron por problema de punto de control

The problem here is a detail of a control point. If…, even if it doesn’t seem to be there, you can sense a red X in the center of the image. But due to the blur you can hardly perceive it. So imagine the precision that can be expected from these images.

Vignetted photo

Problemas de viñeteado en un vuelo fotogramétrico realizado con dron

In this other case, the image is perfectly focused. However, due to a bad adjustment of the diaphragm (at its maximum aperture it is easier to have vignetting problems) and when flying with the sun in the vertical, the image is with one of its edges apparently more illuminated than the rest, producing this result once processed.

Problemas de viñeteado en ortofoto

In this resulting orthophoto you can see the problems that this type of images produce. You can see a series of stripes along the map, coinciding in parallel with the flight lines that were made.

3. Standby failures/control points

From Helixnorth we always recommend the use of topographic ground support by means of gnss technology. In this way our results will always be perfectly georeferenced under the established reference system. Another common error when planning the flight of a drone is that the GCP is not easily recognizable from the images. Many times field technicians use marking tools that are normally used in other tasks, although for this type of work are not the most appropriate.

marcaje con spray de GCP en topografía

The use of spray marks means that when selecting the pixels to which the GCP corresponds, they are not easily recognizable, causing the project to lose precision.

GCP utilizable pero no óptimo en fotogrametría con dron

In this other case a target has been used that helps when selecting those pixels, but in this case appears a problem also mentioned before, the image problems, causing that the GCP is usable, but not in its most optimal conditions.

Now we show you a good example of how a GCP or control point should be.

Buen GCP o punto de control en fotogrametría con dron

In this case the target is perfectly recognizable in its central part, making this way that the precision of our project is in its best conditions.

We hope with this article we have been able to solve some of your doubts when planning the flight of a drone. If you still have doubts about planning a drone flight or image processing, leave us your comment. Ah! And if you want to know the benefits of using drones in topography, we encourage you to read this article.

5 benefits of using drones in topography