[HOT] Suggestions for Helicopter-based Imagery

[Jeffrey Warren]

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.
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstreetmap.org/pipermail/hot/attachments/20110210/188aa826/attachment.html>