[HOT] [info-hotosm] Reference Project #1030 Nepal Earthquake

Thu May 7 09:14:00 UTC 2015

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 <stellargps at 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.htmlÂ
>
> Note some links pointed out there by althio:
> Â http://wiki.openstreetmap.org/wiki/Using_ImageryÂ
> Â http://learnosm.org/en/editing/correcting-imagery-offset/Â
>
> 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.Â
>
> 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 <sbower at gmavt.net> wrote:
>  I don't thinkÂ Chad's IDPÂ 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.leson at hotosm.org >
> wrote:
>  HI Ross, sorry for my delayed response. It is best if you ask your
> questions on the main Hot at openstreetmap.org mailing list.
>
> Chad provided this guidance document on IDPsÂ
> 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 <ross at 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.Â
> 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
>
>
>
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-- 
 [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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