How to make a true orthophoto?

[depeurvince]

Hi, could someone tell me what are the right parameters to make a true orthophoto, it is better from the DEM or from the mesh? And which blending mode? Thanks

[Michel]

Hello depeurvince,

From my experience, I don't think that Metashape is currently able to create true orthophotos. Indeed, it is necessary to know, in addition to the ground, the contours of the buildings, the contours of the roofs with the heights, etc.
While waiting for Metashape to develop this approach, you can create true semi-orthophotos, by having a good DTM, aerial images as vertical as possible, with a very important overlap between images (>80%, even if I prefer 90%) and a perfect exposure allowing to have the least shadow possible. Moreover, the Enable ghosting filter option allows to select the images closest to the nadir, which can help to improve the rendering of the true semi-orthophoto.

[Alexey Pasumansky]

Hello Michel,

From my experience, I don't think that Metashape is currently able to create true orthophotos.

Why do you think so?

True orthomosaic can be generated, if DSM is generated or mesh. If DEM or mesh are being built from the dense cloud, then all the point classes should be used to reconstruct a "true surface" which will be used later for orthomosaic generation.

[Michel]

Hello Alexey,

Indeed, mea culpa, from this point of view Metashape is able to make true orthophotos using the mesh representing the DSM.

In my answer, I was talking about the point of view where we would only have vertical and possibly oblique aerial photos of an area, as part of an aerotriangulation campaign for example, and where the mesh we would obtain would not be precise enough to use it as a DSM and we would only have an accurate DTM at our disposal. This is why I suggested using the most vertical photos possible to avoid distortions.