[Openstreetmap] Free air photo thread

Michael Hallett mistyhill at blueyonder.co.uk
Thu Feb 24 11:06:33 GMT 2005


Dear all

I have used private pilot air photo, and incorporated into GIS.

Private pilot taking air photo out of side window of archaeology sites in 
Ireland and Isle of Man.
Some were very oblique. (She wanted shadows to highlight ridge and furrows)

Did not need GPS in the air.
Used GPS to gather ground control points on the ground, and read coords from 
maps.
Officially I only used GPS!

Mainly used relatively cheap IDRISI (Kilimanjaro now?) to orthorectify, 
(manual typed corespondence files) although have used ESRI and ERDAS, they 
call it georeferencing, but I don't like the wizards (or the licence terms). 
Prefer the control of variables you get with Idrisi, even though it takes a 
while longer.

However you choose to rig up the airplane equipment you still have to post 
process.

I always wanted to use a home made hotair ballon mounted camera, for small 
sites, but never did it.

Multimap is good source of free air photo at around 3.3 m res'
The main problem is the x and y axissss are different scales (to make it 
unuseable) and they change occasionally.
I used PSP to patch them together, and spread sheet to calculate axis 
scales, and enter the axis scales into Arcview.
It works , it's free, but again time consuming.
It's getmapping data and they know I used to do it and my ex colleages still 
do.

Also used GPS and EDM combination to gather high res' 3D to drape the air 
photo over.
It's free, it's ours (no royalties), it's time consuming!

Most free data is GPS based. Car roof mount. Trains someone mentioned this 
month. Poke it out of window to get both sides of a road. Used a submetre 
trimble to get both sides of Wyre forest tracks in Landy, was fun.

I now use Getmapping and Nextmap combo, as I have licence agreements on 
excellent terms to use high res data.

If you don't already use this site; Look at VTP in U.S. for souces of free 
data and lot's of usefull info.

Regards

Michael.






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