[HOT] How bad is mapping from offset imagery?
florian.niel at gmail.com
Tue Apr 4 16:07:02 UTC 2017
I often see that other mappers don't align the background imagery. I am
wondering how a big deal this is.
Aligning the imagery in tasks like the malaria elimination projects is
difficult, if the square does not contain any data (and no gps traces).
I do it (in JOSM) by clicking some points of a road or path or something
other visible in both Bing and the recommended imagery, and check if
there is an offset and then align it to Bing. Then I delete the path I
just mapped and start mapping the buildings.
With this method I need more time for the alignment than for mapping the
two or three buildings to finish the task.
So I have questions:
1) Is there a faster way to align the imagery on empty squares?
2) Is it really necessary to align it for just a few buildings and a lot
of nothing (mapped) around? As I dont know what the data is used for so
I cannot tell. The size and the shape of buildings are correct anyways
and my intention would say it is no big deal if it is a bit offset.
3) Is it possible to align the imagery in advance before opening the
task for HOT so mappers do not have to care about it?
4) Is Bing really always better aligned or are we doing just a shift
from one unknown offset to another?
Another comment on alignment: I just looked at the video from Blake
(https://www.youtube.com/watch?v=1Pcj_wFTHeE) about how to align imagery
in iD. I think we need a better one. One thing is that it is not
comparable to empty squares (like in many malaria-project squares) and
the other thing is that he comes to the conclusion that he should not
align the imagery at all (because it is a messed up square with objects
mapped from different imageries).
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