Ah. That made sense. A little rusty on the maths. Thanks. :) On Fri, Apr 10, 2009 at 12:34 PM, D Tucny <d...@tucny.com> wrote:
> I didn't actually calculate the field of view in degrees, because that > would be harder at this time in the morning ;) working out how much area > they would cover is pretty simple though if you are happy to guess what > resolution camera they used... I went with a 10MP camera, such as a Canon > EOS 1000D, which has an output resolution of 3888 x 2592px... If the > resolution is quoted as 12.5cm per pixel, 3888 of them would be 486m :) > Then, knowing that the picture has been taken from 1676.4m up, making some > more assumptions about the camera being aimed directly at the ground you can > work out all the angles involved as you are dealing with a right-angled > triange with a height of 1676.4m and a base of 243m (half of the 486m worked > out previously), all the information you need :) > > d > > > 2009/4/10 Keith Ng <khensth...@gmail.com> > > How does one go about calculating the field of view from the elevation and >> resolution? Would you mind explaining that? Thank you very much. >> >> On Fri, Apr 10, 2009 at 11:30 AM, D Tucny <d...@tucny.com> wrote: >> >>> 2009/4/10 Ed Avis <e...@waniasset.com> >>> >>>> Pieren <pieren3 <at> gmail.com> writes: >>>> >>>> >>http://wiki.openstreetmap.org/wiki/Aerial_photography_funding_appeals >>>> > >>>> >The wiki says about this supplier: >>>> >About $17 per sq km for basic 2 meter resolution photography. >>>> >>>> Does that mean that each pixel covers an area roughly 2m by 2m? If so >>>> this is >>>> not any better than the Yahoo aerial imagery that OSM can already use >>>> for many >>>> countries. (It could still be worth buying for places not covered by >>>> Yahoo.) >>>> >>>> The aerial photographs used by People's Map are from getmapping.com (in >>>> fact, it >>>> seems to be run by the same people somehow) and those have a resolution >>>> of >>>> either 25cm or 12.5cm. That's the kind of detail that would really help >>>> with >>>> mapping those council estates and car parks. >>>> >>>> < >>>> http://www2.getmapping.com/Support/Aerial-Photography-Coverage-%281999-to-2003%29 >>>> > >>>> >>>> At this detail level they will sell a 10km * 10km area for 1850 GBP. At >>>> least >>>> nine such areas would be required to cover inner London (the area of a >>>> 'Mini >>>> A-Z'). However, this price is for '1 to 10 hard copies' - I don't know >>>> how much >>>> they would want in exchange for providing photos that can be used in >>>> OSM. Since >>>> OSM is a competitor to People's Map, they might ask a lot. >>>> >>>> >>> The reason getmapping has such a high resolution is that they are not >>> using satellites... they capture images from 5500 feet (1676m) according to >>> their site... If they were using a 10 mega-pixel camera, getting a 12.5cm >>> resolution would give them a field of view covering 486m x 324m, or double >>> that for 25cm resolution, they'd have to do a lot of flying just to cover >>> the UK, let alone the rest of the world... In comparison, satellite imagery, >>> which for commercial use currently has a best resolution of 41cm (apparently >>> downgraded to 50cm due to US Government controls) in monochrome, 2.4m in >>> full colour, takes shots that can be 15km wide and hundreds of km long... >>> They do cost a bit to build, launch and manage though... >>> >>> How much does a small plane with camera mount cost to hire for a day? :) >>> >>> d >>> >>> _______________________________________________ >>> talk mailing list >>> talk@openstreetmap.org >>> http://lists.openstreetmap.org/listinfo/talk >>> >>> >> >> _______________________________________________ >> talk mailing list >> talk@openstreetmap.org >> http://lists.openstreetmap.org/listinfo/talk >> >> >
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