[OpenDroneMap-users] "bowl" effect

[Anna Petrášová]

On Mon, Jun 22, 2015 at 6:00 PM, Stephen Mather <stephen at smathermather.com>
wrote:

> 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.
>

I was thinking about compensating for the bias based on the lidar data I
have, but I haven't tried it yet.

>
> 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.
>

There isn't really any gcp in the middle of it:
https://drive.google.com/file/d/0B7CQoT4YE2mMNzJSbEZsaGtrZ3hnRUdPQ3VDbF9DS0o2SS1j/view?usp=sharing

but how could the GCPs help? Georeferencing won't really change the shape,
isn't it just rotation and translation?

All I know about the camera is in a log file I got (I kept just the
relevant part):

https://drive.google.com/file/d/0B7CQoT4YE2mMOHREZ0VMaWliRE0/view?usp=sharing
There was not much information in the exif.

>
> 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.
>
>
I know this alternative exists, but has anyone here used it successfully? I
mean, there is probably some reason why it's not merged yet?

> Cheers,
> Best,
> Steve
>
>
Thanks!

Anna

>
>
>
> 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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>>
>
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