Orthomosaïques ne se traitant pas correctement

McKenzieBredemeyer

J'ai complété un plan de vol dans ArcGIS Flight hors ligne dans la forêt et je l'ai soumis à SiteScan pour traitement, et bien que les images aient été prises correctement sur toute la zone de la mission, l'orthomosaïque présente de grandes zones vides et il y a beaucoup de distorsion à l'intérieur de l'orthomosaïque, pas seulement autour des bords où une certaine distorsion pourrait être attendue. J'ai essayé de retraiter les images plusieurs fois, y compris en les téléchargeant dans un tout nouveau projet, mais rien n'a changé. C'est seulement mon quatrième vol avec ArcGIS Flight/SiteScan, mais mes trois autres vols étaient des missions plus grandes et plus compliquées et pourtant ils ont été traités correctement. Quelqu'un aurait-il des idées et/ou des moyens pour éviter les re-vols à l'avenir ? Version SiteScan 4.210.2, version ArcGIS Flight 5.1, drone DJI Mavic 2 Pro, le plan de vol avait la prise en compte du terrain activée et était complètement hors ligne et rien d'anormal ne s'est produit pendant le vol. Bien que ce soit seulement ma quatrième mission, j'utilise ce drone depuis un an pour prendre des images et il a rarement eu des problèmes pour traiter les images en orthomosaïques dans d'autres logiciels comme DroneDeploy.<\/P>

<\/span><\/P><\/span><\/P> <\/P> <\/P>

NicoBonnafoux

Hi @McKenzieBredemeyer, 

Thanks for raising this, great question and two different yet common scenarios that both pose challenges: 

1 - Mapping forested areas resulting in holes and distortion in the orthomosaic

Dense vegetation (like forest canopy) is one of the most challenging environments for photogrammetry. Even when image coverage looks good, the core challenge is feature matching:

• Forests contain highly repetitive textures (leaves, branches, shadows), which makes it difficult for the software to identify stable, unique tie points between images.
• When confidence in image matching drops, this can result in:
  • Gaps where surfaces can’t be reconstructed reliably
  • Local distortion, not just around the edges

One important nuance, especially given the comparison to other software, is how gaps are handled:

Some photogrammetry engines will aggressively interpolate or “fill in” areas where matching confidence is low. This can make an orthomosaic appear more complete, but those filled areas are often estimated rather than directly supported by strong image evidence, which can reduce accuracy.

With the Reality Engine used in Site Scan, our approach has historically been more conservative. When the software cannot establish sufficient confidence (common in dense or repetitive vegetation) we prefer to leave gaps rather than fabricate detail. From an engineering standpoint, we generally favor exposing uncertainty over hiding it.

That said, we also recognize that large canopy gaps aren’t always desirable for end users. Based on customer feedback, we’re beginning to apply limited, targeted interpolation in heavily vegetated areas, while still prioritizing accuracy and transparency. This is an area of active improvement that has started to be introduced and you will see further enhancements in the two months or so. 

A few practical considerations for future flights in forested environments:

• Increase overlap, which is the single most effective way to improve reconstruction reliability
• Maintain consistent lighting where possible
• If you’re considering a future drone purchase, a platform with a mechanical shutter can also help. Mechanical shutters reduce motion‑related distortion compared to rolling‑shutter sensors (like the one on the Mavic 2 Pro), which can be beneficial in complex, high‑texture scenes such as vegetation
  
  
  

2- Mapping around tall structure/buildings

Flight planning applications, including ArcGIS Flight, calculate overlap assuming the mapped surface is at ground level, based on sensor field of view and planned flight height. When you fly near tall buildings, the effective camera‑to‑surface distance is reduced, which means:

• Each image covers less area on the building surfaces
• Your effective overlap is lower than the planned 70/70, even if photo positions look dense. See the attached illustration: the image capture rate is consistent and desired overlap is achieved at ground level, but the top of building only appears in a single image. 
• This is why holes often appear around rooftops and facades

While crosshatch flights improve viewing geometry, they do not replace overlap when mapping vertical structures.

To compensate, especially when you can’t increase altitude due to airspace restrictions, you should:

• Increase frontlap and sidelap, even for crosshatch missions. You could perhaps fly a separate mission over the building itself with higher overlap, keeping the other area that is near ground level unchanged, then merge the images for processing. 
• Plan overlap based on the tallest features, not just ground level
• When possible, capture both nadir and oblique images. 

Hope this helps, and thanks for sharing the detailed context, it’s a great discussion.

Nico