Bonsoir Pierre,
Thank you for your interesting observations. Indeed, you can find many
problems with the waterways, when you take a detailed view, and
unfortunately now it is often difficult to fix them because the high res
imagery does not seem to be available any more.
I did not know about Yan's list of rivers.
The page suivi-affluents reflects a work a progress (and everyone is
welcome to join in). As explained in my message quoted below, it shows
only waterways that are represented by relations.
Jocelyn has just produced maps showing what is covered in this respect,
and what remains to be done.
http://osm3.crans.org/haiti/images/
http://osm3.crans.org/haiti/images/rivers.png contains waterways (except
streams) with the following color code:
blue = water-way
red = waterway relation without tributary relation
pink = waterway relation with tributary relations, together
light green = (water-) ways that are direct tributaries of waterway
relations
We are discussing it in #osm-fr IRC channel (on irc.oftc.net), and you
are of course welcome to join the discussion.
I guess analysing the main river basins should be the priority.
The DMA maps haiti-tlm-50 (still available as WMS), and Landsat, can
also be useful to map rivers that are missing (likely because they were
not covered by high res sat imagery), and for some fixes.
Opencyclemap can be shown in JOSM with the slippymap plugin, and is
indeed useful for contour lines.
http://www.healthmap.org/haiti/index.php can also be useful to
prioritize attention on cholera affected areas.
Best wishes,
Jean-Guilhem
Le 25/10/2010 19:48, Pierre Beland a écrit :
Jean-Guilhem
The cholera epidemy and water contamination shows the importance of
well identifying the Drainage Bassins in Haiti. These like a tree
leaf, have complex ramifications not easy to analyze. I am not a GIS
specialist and dont know if specialized tools exist to analyse such
ramifications.
Here are some observations following the validation work I did
manually last spring on Haiti Rivers, streams and canals.
The affluents of a river are complex ramifications. See, for example,
http://www.openstreetmap.org/?lat=18.4057&lon=-72.0741&zoom=14&layers=M <http://www.openstreetmap.org/?lat=18.4057&lon=-72.0741&zoom=14&layers=M> .
In such a ramification, its long and tedious to check each
ramification, to validate if directions are appropriate.
To this regard, the Report
http://osm3.crans.org/haiti/suivi-affluents.php shows only small part
of Drainage bassins.
To analyse and build good cartography of Drainage bassins, we have to
consider all the waterways and all ways and nodes connected to. I have
identified waterways with the following tags : river, stream, canal
and drain.
I have often seen ways with the wrong direction (going upward). Yan
report on rivers also shows many small waterway segments not connected
to a Drainage Bassin.
We have to consider the possibility that ways are connected to a River
ramification with wrong tags or are wrongly connected to rivers.
Ideally, we would have to analyse more deeply the river ramifications
and identify different incoherencies, check if all river names are
present.
If useful to identify steep slopes, it could also be possible to add
elevation to each node.
To do efficiently the validation work, it would be necessary to
extract all the nodes and ways connected to river ways and relations.
And badly, that, I dont know how to do with Openstreetmap database. If
it was possible to easily export all the information related to rivers
in a MySQL database, I think that we could do a lot of
validations from that database.
In Yan List of Rivers
(http://www.tappenbeck.net/osm/data4wiki/haiti/haiti-river_wiki.html
), there are still many unnamed segments. Many of them might be
unconnected to other rivers. This list have to be manually updated and
might have not been updated recently.
Opencyclemap contour lines could be usefull to identify river
directions. But rivers are not showed on that map. I dont know if
there are ways to add simultaneously contour layers and river layers
to Openstreetmap.
Exemples of problems
Canal Desdunes (waterway=canal) not connected page
http://www.openstreetmap.org/?lat=19.2867&lon=-72.5855&zoom=14&layers=M <http://www.openstreetmap.org/?lat=19.2867&lon=-72.5855&zoom=14&layers=M>
Many River ramifications not connected
http://www.openstreetmap.org/?lat=18.4397&lon=-71.9705&zoom=14&layers=M <http://www.openstreetmap.org/?lat=18.4397&lon=-71.9705&zoom=14&layers=M>
A stream connected to a road
http://www.openstreetmap.org/?lat=18.4579&lon=-71.8602&zoom=14&layers=M <http://www.openstreetmap.org/?lat=18.4579&lon=-71.8602&zoom=14&layers=M>
Rivers ending nowhere (or in canals ?) in suburb of Port-au-Prince
http://www.openstreetmap.org/?lat=18.5218&lon=-72.125&zoom=13&layers=M
<http://www.openstreetmap.org/?lat=18.5218&lon=-72.125&zoom=13&layers=M>
When looking at zoom level 13,14, you will see well the ramifications
and see a lot of problems with orphan rivers.
------------------------------------------------------------------------
/Pierre Beland /
------------------------------------------------------------------------
*De :* Jean-Guilhem Cailton
*Date/heure :* 2010-10-23 19:34:56
*A :* HOT; Talk-ht
*Cc :* OSM-talk; Jocelyn Jaubert
*Sujet :* Re: [Talk-ht] River system analysis tool for Haiti
Hi,
Jocelyn has setup a page showing the tributaries network for Haiti,
updated from hourly updates if all works well:
http://osm3.crans.org/haiti/suivi-affluents.php
For waterways to appear in it, they have to be represented by relations,
and tagged according to the scheme described in:
http://wiki.openstreetmap.org/wiki/User:Frodrigo/Relation:Waterway
i.e. with tributaries appearing as members of the destination relation,
with role=tributary, and being themselves relations if they have their
own tributaries.
(I have just learned how to add a relation as member of another relation
in JOSM:
- double click the tributary relation in the relations panel, it should
appear in pink in the main editing area;
- single click the destination relation;
- click on the "Modify relation" button).
It is also considered to maybe adapt the page
http://osm3.crans.org/haiti/pyramide-cours-eau.php?osm_id=48998245
(originally authored by Sly, and currently using ways only, not relations)
to build the network from topology information and display it in a table.
Many thanks to Jocelyn (and Frodrigo for discussion).
Jean-Guilhem
News from biosurveillance do not sound good, with
"Confirmation of Cholera at Multiple Sites in Port au Prince"
(http://biosurveillance.typepad.com/haiti_operational_biosurv/)
An extract from yesterday IFRC Information bulletin:
"A team of epidemiologists from the Department of Public Health and
Population (MSPP) was mobilized to
Artibonite to analyze samples taken from several patients to identify
the causative agent of the acute
diarrhoea outbreak. As a result of these analyses, the Ministry
confirmed that Vibrio cholerae is causing the
outbreak and that the source of the contamination is the river."
(http://www.reliefweb.int/rw/rwb.nsf/db900sid/MUMA-8AH3J5/$File/full_report.pdf)
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