[Talk-ca] Simplifying CanVec imports

[Daniel Begin]

Hi Samuel,

 

It might be a good idea to simplify some features before importing.  It is
not necessary for all features, and the feature's node density usually
varies by provinces/theme.  In BC, hydro network is really dense as you
already figured out. In Quebec, the new road network often needs to by
simplified.

 

I would say just do it if it is required for the tile/theme you are
importing

 

Daniel

 

  _____  

From: Samuel Longiaru [mailto:longiaru at shaw.ca] 
Sent: February-11-11 10:38
To: talk-ca at openstreetmap.org
Subject: [Talk-ca] Simplifying CanVec imports

 

Good Morning Everyone,

For the past couple of weeks I have been importing CanVec data into an area
southwest of Kamloops.  There was very little (if any) existing OSM data in
the area.  I've gotten into a bit of a rhythm, merging and stitching all of
92I07 and about half of 92I10 but started becoming concerned about the high
data density, particularly associated with streams in the area.  Most import
files at the level of 92 I 07.0.0 for example, are runnning 10-15k nodes.
At that rate, that is somewhat near 200,000 nodes for an area at the level
of 92I07.  Yikes!  I guess the question in my mind is just how many data do
we want to import at this level and what are the practical implications for
server processing and overload.  I expect that this level would be fairly
consistent across most of Western Canada. Even now, I haven't been able to
call up a complete map in the openstreet.org view tab for the past 4 or 5
days... 25-50% of the map being covered with "... more OSM coming soon"
tiles.

I looked at the Simplify Way function in JOSM and applying it to just the
water data, have been able to eliminate 5-8k nodes from each file, thereby
cutting the data in nearly half.  I really don't see any significant
degradation in the map quality as a result.  Without simplifying, the data
nodes in some places are incredibly (and undeservedly ) dense.  The only
discussion I've been able to find on the simplify tool is some rather old
discussion that took place during development.  

So just wondering if simplifying these data is a reasonable approach.  Right
now, I am going back to the imported areas, calling them up from OSM,
simplifying the water, and re-uploading the simplified data.  In the future,
I will just simplify in JOSM before uploading the file in the first place.
Anyway, does anyone have any issues with my approach here?  Is it worth
simplifying  or am I being overly concerned about data density and its
longer term implications?

Thanks,

Sam Longiaru
Kamloops, BC 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstreetmap.org/pipermail/talk-ca/attachments/20110213/24caeb02/attachment.html>