2013/5/18 Christoph Hormann <chris_horm...@gmx.de> > - imagine mapping something based on satellite images and you > need to use different images for various parts due to clouds or even > the common case of supplementing survey data with Bing images. >
yes, this is very common, at least in regions with alternative high resolution imagery, but it is similar for object and for changeset source tags. For instance "bing" alone doesn't tell you which zoom level you used, but different (high) zoom levels in Bing are based on different aerial imagery (in my area there are years if not a decade in between z20 and z21 and they also have different offsets). I almost always use at least 2 aerial imagery providers (pcn and bing), drawing in one and positioning in the other, in the comment I simply write "...and tracing from PCN2008 and bing". Usually with aerial imagery from webmaps you also don't see from when they are, at least almost nobody stores this information in the source tag, but it is much more relevant (IMHO) to know "traced from aerial imagery from 2007" than "traced from bing aerials" In the end it is almost pointless to compare different aerial imagery layers with each other, what matters is reality and the best way to find out is leave your desk and go out mapping ;-) > - many large objects are included in a lot of changesets without > actually being substantially modified (like moving a single node in a > 500 node way etc.) This means finding the actual changeset a certain > geometry originates from to get the metadata information is not so > easy. > you will see from the changeset that only one node was moved (added or deleted) and this will supposedly be based on your specified "source", generally moving a node will not create a new way version, but I get what you intended (e.g. add or delete a node). IMHO this is a point for associating the source to the changeset, as modifying it on the object after adding this one node will tell the wrong story but not modifying the source tag is neither desirable. The solution in my opinion would be to have separate metadata tags which > are reset everytime a substantial change is made to the data they refer > to unless the user explicitly sets them (either individually or for the > whole changeset). Geometry metadata tags for example would be reset > if: > Your mention of geometry metadata reminds me of another point: a simple "source" is not enough, you'd need a distinct source tag for all properties not one source for the whole object. cheers, Martin
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