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<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=552411914-18112009>A great proposition!</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=552411914-18112009></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=552411914-18112009>- About NTS tiling: Just take into account in
your algorythm that the width of NTS tiling double at latitude 68 and 80 (don't
use fixed longitude values because you will end up with 400 tiles for an
NTS up north !)</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=552411914-18112009></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=552411914-18112009></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=552411914-18112009>- About naming convention, I would propose to use a
number as suffix instead of a letter. It would be easier (for me) to find
neighbour tiles.</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=552411914-18112009></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=552411914-18112009>Example: <SPAN class=552411914-18112009>021E05-18 (with
a 5X5 window)</SPAN></SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=552411914-18112009>Neighbours are 12,13,14,17,19,
22,23,24
([18-6,-5,-4],18-1,18+1,[18+4,+5,+6])</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=552411914-18112009></SPAN></FONT> </DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN class=552411914-18112009>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=552411914-18112009>Example: <SPAN class=552411914-18112009>021E05R (with a
5X5 window)</SPAN></SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=552411914-18112009>Neighbours are
L,M,N,Q,S,V,W,X
(I have no magic to do that!)</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=552411914-18112009></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=552411914-18112009></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=552411914-18112009>- Is it going to work with Canvec as
well?</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=552411914-18112009></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=552411914-18112009>Cheers,</SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=552411914-18112009></SPAN></FONT> </DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2><SPAN
class=552411914-18112009>Daniel</SPAN></FONT></DIV></SPAN></FONT></DIV>
<DIV dir=ltr align=left><FONT face=Arial color=#0000ff size=2></FONT><BR></DIV>
<DIV class=OutlookMessageHeader lang=en-us dir=ltr align=left>
<HR tabIndex=-1>
<FONT face=Tahoma size=2><B>From:</B> talk-ca-bounces@openstreetmap.org
[mailto:talk-ca-bounces@openstreetmap.org] <B>On Behalf Of </B>Adam
Dunn<BR><B>Sent:</B> 18 novembre 2009 01:42<BR><B>To:</B>
talk-ca<BR><B>Subject:</B> [Talk-ca] NTS 1/10,000 Tile
Proposal<BR></FONT><BR></DIV>
<DIV></DIV>This applies only to the band of tiles represented by the 7
southernmost major tiles. That is to say {00-06, 10-16, 20-26, etc}. Once you go
north of that, the tile naming scheme changes, and the following no longer
applies (and is likely no longer needed).<BR><BR>Though many people know how the
NTS naming scheme works, it will be summarized here. NTS tiles are first given a
major number, such as 010 or 093, progressing south to north and east to west.
Each of these tiles is four degrees high (latitude) and eight degrees wide
(longitude). These tiles are then split up into 16 tiles, the so-called
1/250,000 tiles, and given a letter as a name, starting from the south-east
corner then going west and zig-zagging north. Each of these tiles is one degree
high (lat) and two degrees wide (long). Each of these tiles are split once again
into the 16 1/50,000 tiles, each with a number, following the same zig-zag
pattern as the 1/250,000 tiles. These numbered tiles are 0.25 degrees high and
0.5 degrees wide.<BR><BR>So far, the tile divisions have worked out to nice
round numbers. For 1/250,000 tiles the least significant digits are:<BR>lat: {0,
1, 2, 3, ...} and long: {0, 2, 4, 6, 8}<BR><BR>For 1/50,000 tiles, least sig
digits are:<BR>lat: {.00, .25, .50, .75} and long: {.0, .5}<BR><BR>This system
works well, but for the purposes of OSM in high-density areas it becomes
necessary to split NTS tiles up further. Splitting the 1/50,000 tiles up into 16
tiles would follow the NTS splitting scheme, but would result in very strange
numbers:<BR>lat: {.0, .0625, .125, .1875, .25, ...} and long: {.0, .125, .25,
.375, .5, ...}<BR>While there's nothing wrong with this and computers could
handle it easily, it's a little hard on human eyes ;)<BR><BR>If the tiles were
instead split into 25 tiles (5x5), the numbers would work out a little nicer to
the eye:<BR>lat: {.0, .05, .1, .15, .2, .25, ...} and long: {.0, .1, .2, .3, .4,
...}<BR><BR>Thus, the proposal is to split NTS 1/50,000 tiles into 1/10,000
tiles such that each tile is 0.05 degrees in latitude and 0.1 degrees in
longitude. The naming would take on letters A through Y, in a zig-zag pattern
similar to the pre-existing NTS scheme, starting from the south-east corner.
This letter would go in the last position of the tile name, eg. 042I/12A or
092H/04Y. Figure 1 shows an example for 092H/04 (the figure is twice as wide as
it is tall, following an equirectangular projection. In real life, and most
projection methods, the length ratios change with latitude.)<BR><BR>Fig 1: <A
href="http://www.mediafire.com/imageview.php?quickkey=mmmymj42yw4&thumb=4">http://www.mediafire.com/imageview.php?quickkey=mmmymj42yw4&thumb=4</A><BR><BR>Adam<BR></BODY></HTML>