[HOT] Introduction

Alexander W. Janssen alexander.janssen at gmail.com
Mon Jul 7 11:09:34 UTC 2014


On Mon, Jul 7, 2014 at 10:43 AM, Dan S <danstowell+osm at gmail.com> wrote:
> Hi Alex,

Hi Dan!

> 1) Yes, sometimes it's frustratingly difficult with low-res imagery to
> know what you can contribute. I would say DEFINITELY carry on mapping
> those big waterways you mention. In my experience, when we're trying
> to map an unmapped area, having those landmarks in OSM's database
> (waterways, major roads, residential areas) really helps future
> mappers to have points of reference, even if they are approximate and
> need refining later.

OK, will continue with that.

> 2) Re farmlands and forests: I sometimes draw these in, but not often.
> I agree with you that it seems helpful to give a rough picture of the
> landscape to expect, BUT on the other hand, I think having these
> polygons all over can sometimes make the more important jobs harder:
> jobs such as checking that every single building has been captured.
> And since these landuse polygons are pretty much never requested in
> the tasks (apart from landuse=residential which is often a crucial
> first step), it seems the locals and the aid organisations don't
> particularly need them. So I would suggest don't spend much time on
> those.

Ah, allright. Well, I prioritize anyway; if I'm in the mood I'll just
draw it anyway :-)

>                   If you see tasks which seem fairly complete, it
> might be a better use of your time to get yourself to a point where
> you feel confident enough to *validate* other people's completed
> squares. It takes a little while to feel confident about being a
> validator but we always need more validation effort than we get.

Good point; however, when it comes to the validating part, I know how
hard that is in my area - especially when it comes to correct road
relations and the such. There are still many grey areas, as soon as we
run out of unaddressed areas, I'll look other the validation part. So
that more skilled people can concentrate on that first. Also, Is there
a feedback process in case I'm doing something wrong? I guess if I
make a mistake, I'll do the same over and over again. Got the wiki in
another tab open for reference at all times, but well, you know how it
is.

> 3) Firstly, you should indeed tag the changeset with the actual
> imagery you used.

I thought so.

> But secondly, if you're not careful about which
> imagery you use, there's a risk that you might end up tracing from
> imagery that is a couple of years old or something like that.

Luckily Bing shows a date in JOSM and all of it shows 2014 up until now.

> My personal approach would be to try and use the recommended imagery,
> since someone has usually put effort in to working out which imagery
> is most appropriate. Also, there's usually a conversation on the
> mailing list which always gives some clues about what to use.

I paid attention to this, however other people seem to have the same
problem - MapBox/Digital Globe is not exactly high-res. In one
occasion I could use Spot data, but that seems to be rare.

I wonder if it'd be useful to use Sentinel 1-A data? It's free to use
and available at ESA's Sentinel Data Hub. However, the 1-A satellite
was just recently comissioned and the webinterface is a nightmare.
Also, the data products aren't really curated yet, only level-1
products are really useful now and we're speaking about TIFF-blobs
hundreds of Megabytes large. I think these would've to be split to
tiles and zoom-levels first before they're really useful to JOSM.

Information about ESA's Sentinel project:
https://sentinel.esa.int/web/sentinel/home
Sentinel Data hub: https://senthub.esa.int/

Regristration and usage is free.

> Dan

Alex.


-- 
The best thing about procrastinating is you can do it NOW and ANYTIME.



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