Trouble aligning, ower water

[Peter]

I have done a survey with UAS over an area covering 2 square kilometers and the area is both water and land. Over some of the water areas photoscan has trouble aligning the images, i guess that it has to to with to little textures in the images. I guess they all look the same......

Is there a workaround or some setting i can do to improve the result. The images are all geotagged.
I have tried medium and high align setting with same result.

Maybe make two separate projects and align them with different settings and merge the later in globalmapper, or do chunks.

Here is a link to a printscreen showing the exported orto and the missing water in the top and bottom part of the orto, in the middle part there was moore movement in the water so i guess that helped.

Dropbox link
https://www.dropbox.com/s/eb7318cytert44d/River.bmp

[Peter]

Anyone?

What is photoscans limit when it consider the images to be "not valid for matching"

could this value be changed?

I could edit images adding interest points but that is big work

[George]

Tjenare Peter,
If you aim aerial photo only then employ "smooth" instead of "sharp" and "fill holes" as well.
Well ... Water is always a challenge.
H?lsningar, GR

[George]

Ah! Forgot ... Forget about aligning the images it is almost impossible water doesn't contain no points to hook on

[photogrammetrix]

Hi,

the basic principle behind classical stereophotogrammetry as well as for  the 3D scene reconstruction from multiple (aerial) images as Photoscan does, is, to have homologous points - identical object points viewed from different camera positions. In classical photogrammetry this is done by an Operator, who identifies and measures the positions of these points (control-points with known world coordinates as well tiepoints between images). Photoscan manages this by automaticallly extracting potential point canditates by feature extraction algorithms (maybe SIFT, SURF or EPFL DAISY). Their charackteristics are stored in so called feature descriptores which are analysed by statistical means during matching to find matching points.

To conclude: If it is impossible for PS to find enough matching points it cannot do a proper scene reconstruvtion. And for  the following surfaces / Objects this is hard to do or nearly impossible:

- Water, because it is mostly  a moving  surfaces, when it is  not moving, it is textureless and reflects incoming light specular.
- Man made structures without any texture, specular reflective charackeristics  e.g. Metal roofs, glass surfaces, uniform concrete surfaces etc.
- Moving objects like cars on a motoway etc, ships , trains etc

As George suggested, you can use smooth and fill holes, so that the areas where there is no 3D reconstruction possible will be filled. But be aware that ther will possibly be mountains and valleys in your water area.

 We handle it the following way:

During point detection, matching and mesh generation water is masked out. when we have the mesh the masks are taken from the images and Orthofoto is calculated with  the complete images (use fillholes Option) . For your DSM you can fill up the water levels in your GIS software.

Cheers

[Peter]

Tjena George

Yes my problem is that the water look allt the same, no tiepoints. I think i need to manually add markers to images and the realign them. Wishgranter pointed this out to me, it is also in the ps manual.

I will try out the masking aswell and, another idea i have is to go back and fly at an higher alitude so land is visible on the photos. The area is an river so maybe flying at 300m would help, need to do some math.