<div dir="ltr">Ross - If you haven't already, see the recent threads on "data alignment to satellite imagery" and "imagery alignment", in the archives for May:<div><a href="https://lists.openstreetmap.org/pipermail/hot/2015-May/thread.html">https://lists.openstreetmap.org/pipermail/hot/2015-May/thread.html</a> <br><br>Note some links pointed out there by althio:<br> <a href="http://wiki.openstreetmap.org/wiki/Using_Imagery">http://wiki.openstreetmap.org/wiki/Using_Imagery</a> <br> <a href="http://learnosm.org/en/editing/correcting-imagery-offset/">http://learnosm.org/en/editing/correcting-imagery-offset/</a> <br><br>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. <br><br>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.</div><div><br></div><div>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.</div><div><br></div><div>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).</div><div><br></div><div>Steve<br></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Wed, May 6, 2015 at 1:53 PM, Steve Bower <span dir="ltr"><<a href="mailto:sbower@gmavt.net" target="_blank">sbower@gmavt.net</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">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.</div><div class="gmail_extra"><br><div class="gmail_quote"><div><div class="h5">On Wed, May 6, 2015 at 4:35 AM, Heather Leson <span dir="ltr"><<a href="mailto:heather.leson@hotosm.org" target="_blank">heather.leson@hotosm.org</a>></span> wrote:<br></div></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div class="h5"><div dir="ltr"><div><div>HI Ross, sorry for my delayed response. It is best if you ask your questions on the main <a href="mailto:Hot@openstreetmap.org" target="_blank">Hot@openstreetmap.org</a> mailing list. <br><br></div>Chad provided this guidance document on IDPs <a href="http://hotosm.github.io/tracing-guides/guide/Nepal.html#IDP%20Collection%20Guidance" target="_blank">http://hotosm.github.io/tracing-guides/guide/Nepal.html#IDP%20Collection%20Guidance</a><br><br></div><div>Hope this helps<br><br></div>Heather <br><div class="gmail_extra"><br><div class="gmail_quote">On Tue, May 5, 2015 at 12:40 AM, Ross Taylor <span dir="ltr"><<a href="mailto:ross@byrdtechnology.com" target="_blank">ross@byrdtechnology.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">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!<br>
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Note: I tried to adjust alignment but it fixes one area and creates more offset in other areas.<br>
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-Ross<br>
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Sent from mobile</blockquote></div><br></div></div>
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