[HOT] Suggestions for Helicopter-based Imagery

Milo van der Linden milo at dogodigi.net
Thu Feb 10 07:00:27 GMT 2011


One thing I noticed from Jeffreys pictures of the simple rig is the tape to
keep the lens in fixed position: there are lenses available with "fixed
focal length", these would be best to be used for aerial photography! And
the lenses are only a tiny bit more expensive then regular SLR lenses.

hugin is indeed a good tool for this kind of work, but hugin results depend
largely on the "known variables", the more known variables you have, the
better it is.

I was once the secretary of the dutch opengeo stichting (blog.opengeo.nl) we
had a RC helicopter project running. The fact that the project leader failed
to publish why aerial photography with rc helicopters was (not) possible but
simply said: they cannot be used, we will move to building a RC plane was
amongst one of the reasons for me to quit opengeo.nl

If you take this thing serious and want to set up something general, not
just for one area; I would gladly introduce you to a couple of contacts of
mine at ITC Enschede http://www.itc.nl/ a university specialized in
GeoScience for developing countries.


General ideas:

1. Use a camera with fixed focal length lens (or prime lens)
2. Create as much ground control points as possible. Don't forget to take
height into account.
3. Calibrate the camera. Make sure you get the REAL focal length plus all
other parameters as correct as possible as opposed to what the manufacturer
gave as focal length
4. Try to do as much as possible with hugin, their tool is excelent and
their community is eager to help out when you can clearly state requirements
regarding ortho photography

[1] http://en.wikipedia.org/wiki/Prime_lens
[2] http://www.geo.u-szeged.hu/~joe/fotogrammetria/gcp_specs.htm
[3] http://hugin.sourceforge.net/tutorials/calibration/en.shtml
[4] http://hugin.sourceforge.net/



2011/2/10 Jeffrey Warren <jeff at unterbahn.com>

> What's interesting about that technique is that it uses Hugin to
> orthorectify imagery but he mentions that he is manually correcting ground
> control points (GCPs). This almost invalidates the use of hugin, but makes
> sense since what you really want to do is rectify against a reference map,
> so that the data doesn't drift.
>
> Manual stitching has for the most part proved to be much more accurate,
> even for large areas, and especially for relatively oblique imagery. (and in
> fact because in the osm.totor.ph example, he is actually manually moving
> GCPs, he might be better off using a program which allows a reference layer)
>
> Jeff
>
>
> On Thu, Feb 10, 2011 at 12:55 AM, maning sambale <
> emmanuel.sambale at gmail.com> wrote:
>
>> An osmer used this approach in the Philippines:
>> http://osm.totor.ph/
>>
>> On Thu, Feb 10, 2011 at 1:31 PM, george chamales <george at konpagroup.com>
>> wrote:
>> > Hello everyone,
>> > I'm looking for tips / recommendations / suggestions for the ideal way
>> to
>> > collect and process photos taken from a helicopter (full-size, not RC)
>> for
>> > use in OSM.
>> > At the very least we'll have a decent point-and-shoot, a gps, and a
>> > helicopter.  Still waiting to hear what our ceiling is and am trying to
>> hunt
>> > down a bubble level.
>> > Would be great to get some information back soon - there's a possibility
>> > that we could be in the air as soon as Friday.
>> > george
>> > George Chamales
>> > Konpa Group
>> > Mobile: +1 718.288.7718
>> > Fax:  +1 857.488.4002
>> > Skype:  notgeorge
>> > http://konpagroup.com
>> >
>> > _______________________________________________
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>> >
>>
>>
>>
>> --
>> cheers,
>> maning
>> ------------------------------------------------------
>> "Freedom is still the most radical idea of all" -N.Branden
>> wiki: http://esambale.wikispaces.com/
>> blog: http://epsg4253.wordpress.com/
>> ------------------------------------------------------
>>
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