Re: [Talk-ca] Canada building import - Simplification discussion

[James]

Original(1.4GB file size):
9.263 Average points per feature
Points:20346517
Features:2196329

Simplified (20cm) (1.2GB file size):
8.425 Average points per feature
Points:18504036
Features:2196329

Simplified (40cm) (1.1GB file size):
8.07
Points:17741477
Features:2196329

For better statistics on how it affects file size for ontario (which is the
biggest dataset by the way)
The previous link I provided was for the 20cm simplification, I can provide
a link to the 40cm simplification file if needed.
I don't think simplifying about 50cm would be safe/smart as that would be
getting into satellite imagery quality vs what the cities use (plane
overhead gathering high-res imagery)

On Sun, Jan 20, 2019 at 12:44 AM Nate Wessel  wrote:

> I'm changing the subject line to try and retain some clarity for the
> mailing list.
>
> James, thanks for the stats! I'm surprised this didn't remove more points.
>
> Steve, I mentioned earlier that 20cm is where I happened to draw the line
> for the data we imported in Hamilton County, Ohio and I'm not totally sure
> even that was ideal. A bit more than half of the buildings we've been
> importing there have one (damned) extra node which I've been trying to
> remove manually. I may have been a bit too conservative there, as I didn't
> want to lose any part of the geometry. Sometimes there are tiny bay windows
> and the like.
>
> I'm wondering if the scope of this data warrants some analysis of how
> simplification (and perhaps data quality generally) varies geographically.
> It seems quite likely that every municipality would have it's own quirks,
> and we might want to treat some places differently.
>
> Best,
> Nate Wessel
> Jack of all trades, Master of Geography, PhD candidate in Urban Planning
> NateWessel.com 
>
> On 1/19/19 7:24 PM, OSM Volunteer stevea wrote:
>
> On Jan 19, 2019, at 3:47 PM, James  
>  wrote:
> Resending because these emails are getting over 40KB in size and talk list is 
> spazzing out:
> Original:
> 9.263 Average points per feature
> Points:20346517
> Features:2196329
>
> Simplified (20cm): 8.425 Average points per feature
> Points:18504036
> Features:2196329
>
> Choosing 20cm or higher or lower is where the "improvement?" line gets drawn.
>
> In round numbers of nodes, call this a "10% reduction."  The question is, are 
> the results "improvement?"  If so, it seems worth doing.  (Only one person's 
> opinion, of course).
>
> Steve
>
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[Talk-ca] Canada building import - Simplification discussion

[Nate Wessel]

I'm changing the subject line to try and retain some clarity for the 
mailing list.


James, thanks for the stats! I'm surprised this didn't remove more points.

Steve, I mentioned earlier that 20cm is where I happened to draw the 
line for the data we imported in Hamilton County, Ohio and I'm not 
totally sure even that was ideal. A bit more than half of the buildings 
we've been importing there have one (damned) extra node which I've been 
trying to remove manually. I may have been a bit too conservative there, 
as I didn't want to lose any part of the geometry. Sometimes there are 
tiny bay windows and the like.


I'm wondering if the scope of this data warrants some analysis of how 
simplification (and perhaps data quality generally) varies 
geographically. It seems quite likely that every municipality would have 
it's own quirks, and we might want to treat some places differently.


Best,

Nate Wessel
Jack of all trades, Master of Geography, PhD candidate in Urban Planning
NateWessel.com 

On 1/19/19 7:24 PM, OSM Volunteer stevea wrote:

On Jan 19, 2019, at 3:47 PM, James  wrote:
Resending because these emails are getting over 40KB in size and talk list is 
spazzing out:
Original:
9.263 Average points per feature
Points:20346517
Features:2196329

Simplified (20cm): 8.425 Average points per feature
Points:18504036
Features:2196329

Choosing 20cm or higher or lower is where the "improvement?" line gets drawn.

In round numbers of nodes, call this a "10% reduction."  The question is, are the results 
"improvement?"  If so, it seems worth doing.  (Only one person's opinion, of course).

Steve
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