Springfield, You raise important points, and are not "raining on a parade". The resulting data will not be suitable for all purposes, but it can be very useful for this crisis response.
I do think there is significant risk that some mappers will map directly from un-rectified imagery, and introduce problematic location errors. That needs to be minimized, e.g., through clear instructions and good validation. I think there's room for improvement on the instructions, e.g., it would be good to have a wiki page on mapping from un-rectified imagery in combination with rectified imagery, for crisis response. Thanks On Thu, May 7, 2015 at 5:14 AM, Milo van der Linden <m...@dogodigi.net> wrote: > Hello Springfield Harrison, > > As a 20 year GIS veteran I understand what you say. I do agree that in > communication with first responders it is important to have them clearly > understand that the accuracy of features can be off ~100m. But for them > having maps that give a good indication is way better then having no maps > at all. In the end, and that is what I hope for, it can save lives. > > I have a long running discussion with y'olde GIS community on "how can a > map created by amateurs be better then what we professionals do?". It is my > opinion that it can be. I believe that "the many are smarter than the few" > (quote by James Surowiecki). And the HOT tasks have all the ingredients to > succeed: > > 1. There is diversity of opinion > 2. People involved in the mapping process have opinions not influenced by > those around them > 3. People operate decentralized > > The only thing that might need more attention (and this is where > geospatial experts can take their role) is that HOT and openstreetmap as a > whole could use more mechanisms to turn all these little "private > judgements" into collective quality. This process could involve analysing > quantity and different representations of the same feature through time. In > that way, you could see the mapping activity (in dense area's) as GPS. > There are faults, influenced by methodology, opinion and conditions. And as > a GPS professional, you know that it is _knowing the error_ that > automagically creates accuracy. I would love the GIS/GPS community to think > about how to know the error in community mapping. > > I love this new way of mapping. It creates new opportunities. It involves > new ways of thinking. It is not influenced by what GIS people say GIS > should be like. > > Kind regards, with respect, > > Milo > > > https://en.wikipedia.org/wiki/The_Wisdom_of_Crowds > > 2015-05-07 10:21 GMT+02:00 Springfield Harrison <stellar...@gmail.com>: > >> Hello Steve, >> >> Sorry to rain on the parade yet again but I find this matter of >> image alignment to be puzzling and concerning. >> >> One of the first things I learned when embarking upon GIS/GPS >> mapping was that accurate georeferencing of all layers, but especially the >> base layers (imagery in this case) was sacrosanct. If things are not in >> their correct point in space, what use is that to the end user? Especially >> in rugged terrain, with difficult access and rapidly changing stream flows, >> it is important to know where a trail or road really is. Why try to cross >> a raging torrent when you don't need to? >> >> Having untrained users realign the imagery willy-nilly is >> amazing to me. What faith can anyone have in the new tracings if the earth >> is literally moving every time a new user opens up the file? Accurate map >> datums and projections were created for a reason. >> >> How is it that, "...the DigitalGlobe 2015-05-03 (DG) images have >> had minimal georectification.." This is bizarre, this is not GIS, this is >> merely sketching. Why is such imagery being offered and accepted? I know >> that this is a major emergency but then all the more need for quality data. >> >> However, I am newly arrived, and it seems that most people are >> content with a world that can be up to 200 m out of whack. I'm not sure if >> I can contribute much under the circumstances other than this gloomy >> criticism. Sorry, will try not to dampen the enthusiasm further. >> >> Thanks for your patience, Cheers . . . . . . . . Spring >> >> >> >> At 06-05-2015 11:59 Wednesday, Steve Bower wrote: >> >> Ross - If you haven't already, see the recent threads on "data alignment >> to satellite imagery" and "imagery alignment", in the archives for May: >> https://lists.openstreetmap.org/pipermail/hot/2015-May/thread.html >> >> Note some links pointed out there by althio: >>  http://wiki.openstreetmap.org/wiki/Using_Imagery >>  http://learnosm.org/en/editing/correcting-imagery-offset/ >> >> Because the DigitalGlobe 2015-05-03 (DG) images have had minimal >> georectification (needed mainly for elevation distortion), they may be >> offset by 100m or more. On one tile (5.5km wide) I saw offsets relative to >> Bing of 125m to the west and, elsewhere, 85m to the east. The offsets may >> vary considerable even in nearby areas, especially in steep terrain. >> >> You should align your work with Bing imagery. Thus to digitize from the >> DG imagery you should first adjust the DG imagery to the Bing imagery, and >> re-adjust it as you move from place to place. As you noted, adjusting in >> one area makes it worse in others, so you have to keep re-adjusting as you >> go. You should be able to compare the Bing and DG imagery to confirm where >> a feature visible on DG is located on the Bing imagery (if Bing is clear >> enough). I try to adjust based on buildings, or road intersections/curves >> (keeping in mind that roads are sometimes relocated), or even less >> permanent features (rivers generally are not good, they move around to >> much). It's a time-consuming process, but needed to correctly locate >> features. >> >> It's not essential that everything be within a few meters of its true >> location, but features should be mapped correctly relative to one-another. >> >> The links above provide guidance on how to align imagery to correct >> locations. It's easy in JOSM with the Imagery Offset tool (on the toolbar). >> >> Steve >> >> On Wed, May 6, 2015 at 1:53 PM, Steve Bower <sbo...@gmavt.net> wrote: >> I don't think Chad's IDP guidance document (though very helpful) >> addresses the issue of spatial accuracy of the DG imagery, raised by Ross. >> I'm going to post that as a separate issue with more detail. >> >> On Wed, May 6, 2015 at 4:35 AM, Heather Leson <heather.le...@hotosm.org >> > wrote: >> HI Ross, sorry for my delayed response. It is best if you ask your >> questions on the main Hot@openstreetmap.org mailing list. >> >> Chad provided this guidance document on IDPs >> http://hotosm.github.io/tracing-guides/guide/Nepal.html#IDP%20Collection%20Guidance >> >> Hope this helps >> >> Heather >> >> On Tue, May 5, 2015 at 12:40 AM, Ross Taylor <r...@byrdtechnology.com > >> wrote: >> Hi, I am seeing many more IDP sites using DigitlaGlobe imagery vs Bing. >> I can toggle between the two image sets, but they are significantly >> nonaligned. I created a landuse=brownfield tagged area which aligns with >> Bing, but if I mark and tag the individual IDP sites showing up in >> DigitalGlobe imagery, the brownfield and idp are not going to be aligned. >> I want to help out as much as possible and would like the data to be >> correct. Please advise, thanks! >> >> Note: I tried to adjust alignment but it fixes one area and creates more >> offset in other areas. >> >> -Ross >> >> Sent from mobile >> >> >> >> _______________________________________________ >> HOT mailing list >> HOT@openstreetmap.org >> https://lists.openstreetmap.org/listinfo/hot >> >> >> >> _______________________________________________ HOT mailing list >> HOT@openstreetmap.org https://lists.openstreetmap.org/listinfo/hot >> >> >> _______________________________________________ >> HOT mailing list >> HOT@openstreetmap.org >> https://lists.openstreetmap.org/listinfo/hot >> >> > > > -- > [image: http://www.dogodigi.net] <http://www.dogodigi.net> > *Milo van der Linden* > web: dogodigi <http://www.dogodigi.net> > tel: +31-6-16598808 >
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