Re: [OSM-talk] Imagery parallax error in high altitude areas
On 2012-04-10 13:45, Arun Ganesh wrote: Is there an accurate source for the coordinates of mountain peaks? We can check how bad the parallax errors are on the satellite imagery. Would it even be possible to identify mountain peaks on satellite imagery? I've been looking at Mont Blanc and Everest and I can not tell from the images where the peak should be. A source of coordinates is Wikipedia of course. No idea how definitive that data is though. Regards, Maarten ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk
Re: [OSM-talk] Imagery parallax error in high altitude areas
> > It's not as bad as it seems. Imagery is adjusted using an elevation dataset. Since this data doesn't (and shouldn't) include buildings and bridges, these appear distorted. You'll also see problems where recent heavy construction has caused changes in topography. Yes, but every pixel is not corrected. An imagery tile of 1km x 1km would possibly be corrected for the average elevation in the area, but in mountainous terrain, the variation in elevation above and below the average would mean that many parts of the tile that we see are actually slightly offset from the actual position. Is there an accurate source for the coordinates of mountain peaks? We can check how bad the parallax errors are on the satellite imagery. ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk
Re: [OSM-talk] Imagery parallax error in high altitude areas
Nathan Edgars II writes: > It's not as bad as it seems. Imagery is adjusted using an elevation > dataset. Since this data doesn't (and shouldn't) include buildings and > bridges, these appear distorted. You'll also see problems where recent > heavy construction has caused changes in topography. Or where the elevation dataset doesn't include a deep canyon, which causes a straight bridge to appear curved. If it's a railroad, you can be pretty sure it isn't. If it's a road bridge, you have to rely on what you saw when you were there. -- --my blog is athttp://blog.russnelson.com Crynwr supports open source software 521 Pleasant Valley Rd. | +1 315-600-8815 Potsdam, NY 13676-3213 | Sheepdog ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk
Re: [OSM-talk] Imagery parallax error in high altitude areas
On 4/1/2012 10:53 AM, Arun Ganesh wrote: It recently struck me while identifying mountain peaks in the himalayas that something may not be right. All of us have noticed that the top of skyscrapers is off from the base of the building owing to parallax error of the satellite capturing the image at an angle. The average seems to be around a 0.2m displacement for every 1m increase in height (based on calculations made in a couple of cities in India). For an imagery tile which has 1000m variation in elevation, various objects could be displaced by as much as 200m from its real position. It's not as bad as it seems. Imagery is adjusted using an elevation dataset. Since this data doesn't (and shouldn't) include buildings and bridges, these appear distorted. You'll also see problems where recent heavy construction has caused changes in topography. ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk
