[OpenDroneMap-users] "bowl" effect

[Stephen Mather]

Ah, ugly. Well, pretty really, but ugly from a data perspective. So
systematic bias in structure from motion is an issue with all systems, and
difficult to overcome with drone imagery in particular, if the drone is
flown in a single Z plane, particularly over relatively flat terrain.  This
is an indictment of the data, just stating a known difficulty. This is why
balloon and kite flights, aside from areal coverage, are so pleasant to
process -- plenty of x, y, and z movement, so less chance for systematic
bias. I've been wondering if once a dataset like Open Terrain (a global
highest-available) is available, if it might be helpful for compensating
for bias in datasets, and also help with data classification pipelines that
can have separate meshing mechanisms for ground, vegetation, and human
structures.

That said, let's get a little more context on the dataset and processing --
did you use ground control and if so, how was it distributed? It would be
interesting to know if you had ground control in the center of the scene,
if ODM is ignoring this extra info. Also, what kind of camera is it? It is
possible that the three parameter corrections that ODM is performing are
inadequate, and a 6-parameter model would be better.

Finally, if you have the time, try processing through the OpenSfM pipeline
https://github.com/OpenDroneMap/OpenDroneMap/pull/50 . It uses a
6-parameter model, and some alternate assumptions for SfM in general.

Cheers,
Best,
Steve




On Mon, Jun 22, 2015 at 10:26 AM, Anna Petrášová <kratochanna at gmail.com>
wrote:

> Hi,
>
> I was comparing a georeferenced DSM generated from ODM mesh with a DEM
> derived from lidar data. The results look great except for this big
> distortion - the picture shows the difference (lidar - odm). I know this
> happens also with DSMs created by Agisoft. Does anybody know where does
> this come from? Is there there any hope this could be fixed in the future?
>
>
> https://drive.google.com/file/d/0B7CQoT4YE2mMcU9PRDYzUFRMVlU/view?usp=sharing
>
> Thanks!
>
> Anna
>
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