I agree.In JOSM, it helps sometimes to switch to the Opencyclemap layer to see
elevations when we have not a clear image, shadow or other obstacle.
Shadow will be a problem in narrow valleys. I have seen this looking at the
Langtang valley surrounded by high summits.
Pierre
De : Pat Tressel <ptres...@myuw.net>
À : john o'l <ol.john...@gmail.com>
Cc : hot <hot@openstreetmap.org>
Envoyé le : Lundi 4 mai 2015 9h36
Objet : Re: [HOT] What's water?
John --
Having mapped a number of streams over the past years, I guess the first thing
to say is that it is surprisingly difficult. Mapping the same watercourse at
different scales can have very different results and the stream channel itself
can change considerably with any given flood event. Aerial, satellite, and
topographic maps each have their own strengths and weaknesses as the basis for
stream/river delineation. As a mapping consolation, since they move around so
much and vary so much over time, approximations at the scales we are using
should be good enough.
One of the things to keep in mind is the reason we are mapping watercourses. In
our current context, when I map one, or even study one in high resolution
photos, I usually think of them as a potential source of water for nearby
inhabitants, as travel obstacles potentially restricting crossings to
particular locations or structures, and as a pathway along which very
destructive events can occur - from floods to mudflows to debris torrents.
I've yet to successfully load the hiu layer anywhere - ongoing JOSM struggles
Imagery -> Image Preferences
Click the TMS button on the lower right. In the popup:
Enter the above URL in box 1., but ==> take off the "tms:" <==, because it will
add that for you.
Enter a name for the imagery in box 4 -- this is what will appear in the menu.
Click OK.
but after a quick check of the coordinates you gave in Google Earth I can say
unequivocally that it is stream or for OSM purposes a river.
There's definitely a river -- I'm trying to pin down whether the water is in
the narrow channel at the west side of the dark region in the above image, or
if there is actually water flooding out over a large area.
I suspect what you are seeing is mostly a result of shadow, which often makes
aerial and satellite imagery challenging - streams are often shadowed given
they occupy the lowest areas in a landscape and mountains/steep valley walls
cast great shadows.
True, the shadow could be from the angle of the land, not just the trees. That
would hint that there should be less shadow where the river is flowing toward
the southeast, as the sun is shining from south-southeast. If the above
procedure works, have a peek.
btw, for a cool feature, about 1 km to the SSW is an alluvial fan!
Ah!
-- Pat
_______________________________________________
HOT mailing list
HOT@openstreetmap.org
https://lists.openstreetmap.org/listinfo/hot
_______________________________________________
HOT mailing list
HOT@openstreetmap.org
https://lists.openstreetmap.org/listinfo/hot
