[Talk-ca] Canvec tile splitter 999x33 a to y 5x5 and/or put on adedicated API?

[Daniel Begin]

Hi Sam and all 

I'm wondering if the best tiling is a fixed number of tiles (5X5) or if it
should be defined as a maximum size of some type for a tile.  

Using JOSM/Canvec files, I worked in high density urban areas where a 4X8
tiling was almost insufficient.  For some rural areas, a 2X2 tiling was just
fine. A 5X5 tiling for Canvec is just an averaging of needed tiling value! 

Knowing an optimal size value for default JOSM configuration, we could tile
any type of data using a Quadtree algorithm

http://en.wikipedia.org/wiki/Quadtree

Let suppose the optimal tile size is 2M (the initial tile is the file)

For each tile:
  Is processed tile size < 2M?
  Yes: then there is no need for sub-tiling - stop processing the tile
  No : Split the processed tile 2X2 then repeat the process

You would end up with 1, 4, 12, 16 ... tiles having a file size < 2M with
some of the tiles covering 1/48, other 1/4 of the processed area!  Using
Canvec data, I would be surprised that tiling needs to go deeper than 8
levels (1/48) for some of the tile.

What would be this optimal size for JOSM? Kilobytes, nodes, feature? I don't
know!  Even the number of members in Relation seems to affect JOSM.

If we can find some hard facts to define it, this could be implemented as
the tiling algorithm.

Cheers,
 
Daniel


 (-Xmx256M) 
-----Original Message-----
From: talk-ca-bounces at openstreetmap.org
[mailto:talk-ca-bounces at openstreetmap.org] On Behalf Of Sam Vekemans
Sent: March 28, 2010 12:26
To: imports at openstreetmap.org; Talk-CA OpenStreetMap
Subject: [Talk-ca] Canvec tile splitter 999x33 a to y 5x5 and/or put on
adedicated API?

Hi all,
We are getting more progress on Vancouver Island, thanks to (haitelk)
who has just added in more wooded area. And the new CVRD data is in
the planning, discussing & sorting data phase. :-)

What we still need todo is make a tool that will automatically slice
the NTS tiles (canvec .osm files) into 25 pieces, so then a local area
mapper can easly take 1 square at a time & work with it, choosing the
data that they need to add in.


I think that OSmosis has this ability, has anyone varified this?
This will be of great help to everyone, as we are also using the
Toporama WMS layer to be tracing & using it for reference.

Otherwise, if we dont have the 1/25th tile area, its harder to ensure
that no 'bulk_implopping' happens where the user gets lazy and doesnt
bother to check the area 1st.

Since the 1/25th tile size is a standard JOSM working space, we would
(just about all of the time), have only 1 mapper is working at a time.
(even in the big cities, this size is managable).

Oh, this whole CanVec dataset would be great to host on a different
API, (like i talked about on my last message for OpenImportsMap does
anyone know if perhaps the devAPI would be a good place for it? Or
should we make a new one that is dedicated to wholesale imports?

Thanks,
Sam
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