[Openstreetmap] Areal photos for free?

Petter Reinholdtsen pere at hungry.com
Fri Feb 18 16:19:52 GMT 2005


Yesterday, I talked to a friend about the Openstreetmap project.  He
happened to pilot in his spare time (cesna), and he liked the idea of
taking aerial photos while he was flying.  All we need is a way to
clamp the camera to the plane, make sure a GPS is included, and
collect photos.  Perhaps there are friendly pilots in the London area
as well?

I've started taking some notes on what is needed.


Aerial photos for free
======================

We can get aerial photos for free by contacting friendly small plane
pilot, and get them to bring photo equipment on their trips.

What should the equipment look like?

 - gps
 - camera (still/video?)
 - laptop for storage
 - correct clock (why?)
 - the shape need to be aerodynamic
 - simple mounting and dismounting on wing or wheel (norsk: stag)
 - barometric height
 - what resolution do we need for the camera

Start with a fairly large (1.5 liter) bottle, to get some fairly
aerodynamic shape.  Cut it open, remove one part of the side (for the
view window).  Place the camera and the gps inside this bottle
(fastened on a plane, showed into the bottle?), close to each other.

The camera and the gps should be close to each other to make sure the
position error of camera matches that of the position error of the
gps.  (Is this really necessary, if the relative position of the GPS
and the camera is know?)

Need to find a way to fill the window area.  Plexiglass?

Use a USB or firewire (DV) camera and a USB GPS, connect them to a
laptop.  Write some software to collect pictures and GPS position as
often as possible.  What resolution and frame rate is interesting?
Depends on the plane speed, I guess.

How do we find the height?  GPS height are very inaccurate, and
barometric height are not directly related to the geoid or ellipsoid
height.

Sketch:

          +------------------+
         /
   +----+        GPS
   |       -----------------
   +----+       Camera
         \        ||
          +---+ window + ----+

Error factors
 - position error
 - camera angle
 - ray bending through window
 - lens distortion
 - camera pixel size / skew




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