[HOT] Suggestions for Helicopter-based Imagery

Jeffrey Warren jeff at unterbahn.com
Thu Feb 10 15:01:54 GMT 2011


- I'd say that Photoshop+GDAL yields the best results, with full warping
ability in Photoshop resulting in much better warps than the affine-based
tools in other packages. It is time consuming, however.

- Autopano Giga can help with under 100 photos, but more than that and you
need a supercomputer. It's about $300, but results in pretty good automated
stitches: http://www.gigapan.org/gigapans/c768bab4245a5671a0b1db569e9668c7/

- Cartagen Knitter is free, but lacks anything besides 4-point projective
distortion, and doesn't do edge blending. It does however export a TMS or
GeoTiff, and works for relatively large sets. Here's one of a 5.5km swath
which we've then imported into JOSM:


That last one was with a balloon rig.


On Thu, Feb 10, 2011 at 9:55 AM, Jeffrey Warren <jeff at unterbahn.com> wrote:

> Not to contradict, but you can certainly get centimeter precision. Accuracy
> of course depends on the accuracy of your reference data, whether GCPs or
> reference imagery. We regularly get up to 2-3cm precision in the Gulf of
> Mexico.
> Here is a section from our draft Grassroots Mapping curriculum -- near the
> bottom there are some good tables describing field of view for a few camera
> types, and the kinds of things you'll want to think about:
> http://publiclaboratory.org/wiki/mapping-curriculum-introduction
> Hugin's rectilinear features are available only in the most recent version
> and the interface is rather obscure. It also depends on known GCPs, which
> for a large flight is impractical. It is much more effective and efficient
> to simply use reference map imagery, especially since it is difficult to get
> good precision on GPS readings for your GCPs.
> Therefore, hugin is only useful for *very* large image sets, and then GCP
> collection becomes impractical. The alternatives are:
> - Manual stitching in Photoshop using a spher. mercator reference map, with
> GDAL post-processing
> - Auto Pano Giga (vouched for by kite mapper Nathan Craig)
> - Cartagen Knitter (http://cartagen.org/maps) for crowdsourced online
> manual stitching, with GeoTiff & TMS output
> Stewart is out of town right now, unfortunately, but I'd be more than
> willing to help you get started on image processing.
> Jeff
> On Thu, Feb 10, 2011 at 9:32 AM, Milo van der Linden <milo at dogodigi.net>wrote:
>> Use hugin, it will give you the best orthorectification for "free". If you
>> want to use professional software; 10.000 euro per license is not enough....
>> You have to decide what quality you need at what price. Centimeter accuracy
>> is nonsense, with the way you propose gathering photo's you should be happy
>> with a meter accuracy which will perfectly fit the purpose in my opinion.
>> Another GIS tool tailored for image processing is ILWIS
>> http://www.itc.nl/news_events/archive/research/0011.asp it has become
>> open source, windows only. Visit the page for more info.
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