[OpenDroneMap-users] "bowl" effect

[Alex Mandel]

On 06/22/2015 06:24 PM, Anna Petrášová wrote:
> 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?
>

The ODM format for a GCP file is X,Y,Z so yes there is height data if
you are providing GCPs. Of course if the Z is provided from a standard
GPS unit that might not be super useful.

-Alex