On Thu, Apr 9, 2009 at 7:31 PM, D Tucny <d...@tucny.com> wrote: > 2009/4/9 Mike Collinson <m...@ayeltd.biz> > > At 11:26 AM 9/04/2009, Eugene Alvin Villar wrote: >> >Hi all, >> > >> >I was doing some cleaning up and some building mapping in the Makati CBD >> area and I noticed that the satellite imagery in Yahoo! (provided by GeoEye) >> has some really bad stitching (multiple satellite imagery were stitched into >> one "seamless" mosaic). One particularly bad example is that Rufino St. >> (Herrera) is broken along Ayala Avenue. The stitching of the imagery seems >> to be along Ayala Avenue and Buendia. If you'll check out the parts of >> Buendia near the RCBC Plaza, you'll notice that there are two shadow images >> of Buendia there. >> > >> >I think this means that the data in the Makati CBD area might be quite >> off in some parts. I think that we need to supplement this with some really >> good GPS traces (the existing uploaded GPS traces are quite noisy) but the >> problem is the urban canyon effect that makes GPS a bit ineffective in this >> area. >> > >> >What do you guys think? >> >> I tried GPS mapping in Makati CBD before the imagery was available and >> found the GPS quality just awful, you are very polite :-) . I had a similar >> problem in Sydney CBD coupled with very oblique aerial imagery that obscures >> many of the roads. The best solution I came up with was to wander about and >> take lots of digital photographs down streets and then iteratively edit the >> map to get relative position looking right against the photos with the few >> spots of good imagery and GPS as a control for absolute position. >> >> Mike >> > > If it's possible to get onto the roof of some of the buildings, you could > get some longish term averaged GPS fixes, and, if you can get ontop of some > of the tall buildings, some aerial photos :) > > The urban canyon effect is going to pretty much rule out getting 'really > good GPS traces' as you'll notice that doing everything you can to get good > signal, the trace will still be all over the place... Maybe in a few years > when GPSrs are better and you can use Gallileo and the US GPS together then > you'll be able to get something half decent, but, for now, creative thinking > and as Mike says, plenty of photos are probably the only way to get a > reasonable level of accuracy... > > d >
I actually thought about going to the rooftops of selected buildings to get absolute fixes for these points. Then lay out everything else relatively. But knowing about paranoid security, it'll be hard to access the rooftops of the right buildings. :-P I'll do some research on which buildings are generally access=permissive to the rooftop. :-) Eugene / seav
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