[HOT] [Talk-ca] Flooding in Richelieu River, Quebec, Canada :Follow-up(Complement of information)

Daniel Begin jfd553 at hotmail.com
Fri May 27 20:17:50 BST 2011

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


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





From: Brent Fraser [mailto:bfraser at 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)



  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

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?





From: Pierre Béland [mailto:infosbelas-gps at 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

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