Hi all,
I've tried to "put my boots on the ground" without going there !-). I found a pretty clear satellite image of the river at its max level (30-31m) - which doesn't really changed since ... http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=50577 I made few geometric adjustments to the image and compare the result with 30m GeoBase and SRTM contours. Geobase contours gives better results between St-Jean and L'Île aux Noix but from there to the US boundary, neither GeoBase nor SRTM is right. I'm trying to produce a flooded area from DEM data while I'm looking at an image that contains what I'm looking for - the flooded area! Why not mapping from it? I understand the image can be used - http://earthobservatory.nasa.gov/ImageUse/ Any idea on how I can use this GeoTiff image in JOSM? Cheers, Daniel _____ From: Daniel Begin [mailto:jfd...@hotmail.com] Sent: May-27-11 15:18 To: 'Brent Fraser' Cc: 'HOT Openstreetmap'; 'talk-ca' Subject: Re: [Talk-ca] [HOT] Flooding in Richelieu River, Quebec,Canada :Follow-up(Complement of information) Bonjour Brent, Which one is better in this situation, SRTM or GeoBase? I would prefer SRTM for the following reasons... SRTM has 90m cell size but the data in each cell are "real elevation" - including roof tops and crop height !, Geobase has 30m cell size but the data in each cell is an interpolation between adjacent contour interval from 50K map. So, in flat/low hills areas, SRTM will give a much better idea of the height than Geobase. For example, a 8m hill, standing between elevation 31m and 39m won't be visible in Geobase data. Same reasoning for a steep cliff, and so on... Furthermore, I suspect that using the 30m contour from SRTM might be valid for St-Jean-Sur-Richelieu area but the 31m should probably be used near Lake Champlain. In this case I would quote James Ewen, You need to "Put your boots on the ground" to decide which one is valid !-) I'm also looking at converting this into .gpx format as proposed Richard Cheers, Daniel _____ From: Brent Fraser [mailto:bfra...@geoanalytic.com] Sent: May-27-11 14:19 To: Daniel Begin Cc: 'Pierre Béland'; 'HOT Openstreetmap'; 'talk-ca' Subject: Re: [Talk-ca] [HOT] Flooding in Richelieu River, Quebec, Canada :Follow-up(Complement of information) Daniel, The SRTM data has 90m cell size, while the CDED (from the Geobase site) has 30m cells (and 1m height resolution) which might rendered better contours. Best Regards, Brent Fraser On 5/27/2011 11:52 AM, Daniel Begin wrote: Bonjour tous le monde, I have generated a 30m and 31m contour lines for Richelieu river and lake Champlain (using SRTM data). It fits the 30m contour provided by Jean-Guilhem but doesn't seem to fit pretty well the flooded wetland area provided by Pierre. Any idea if this data can be used (usgs licence point of view)? And if it can be usefull? Daniel _____ From: Pierre Béland [mailto:infosbelas-...@yahoo.fr] Sent: May-27-11 12:40 To: HOT Openstreetmap Cc: talk-ca Subject: Re: [HOT] [Talk-ca] Flooding in Richelieu River, Quebec,Canada :Follow-up(Complement of information) Jean-Guilhem Cailton wrote on 2011-05-27 > According to the shapefile data, Lake Champlain, and hence Venise-en-Québec are above the 30 m elevation. > The shapefile contains punctual elevations of 31 m in this area (Plage Missisquoi, for example). > The next contour line would be the 40 m one, but it does not look like it would be very useful for this. This is exact. The 40 meter contour line is not usefull for us. Thanks Jean-Guilhem. Pierre Béland _______________________________________________ Talk-ca mailing list Talk-ca@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-ca
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