[Xastir] US Topo GeoPDF?

[Fred Hillhouse]

Sorry for top posting. Well, not really. It is easy for Outlook users. :)
Lookout!


Inverted Y involves a calculation posted near the bottom of my last reply.
It is repeating below as well.

In this case, the address is Z/Y/X rather than Z/X/Y. Another issue, besides
addressing, the tile is a JPG rather than a PNG.

Using OSM, here is a tile address, Z/X/Y:
http://c.tile.openstreetmap.org/12/1236/1513.png

Using ArcGIS, it would be this tile, Z/Y/X:
http://services.arcgisonline.com/ArcGIS/rest/services/USA_Topo_Maps/MapServe
r/tile/12/1513/1236

Notice X and Y are in opposite places? They are the same values, just
reordered.

Inverted Y would be:
...12/2582/1236

For an example of a Visual Flight Rules tile, Z/InY/X:
http://vfrmap.com/20120308/tiles/vfrc/12/2582/1236.jpg


To the best of my knowledge, that is what is meant by "Inverted Y". I may be
wrong but it makes sense when the tile scheme is considered.

Inverted Y = (2^Z-1) -Y [Note: Z = zoom level]

For the VFRMAP example, 2^12-1 = 4095. Subtract off the Y of 1236 and you
get 2582: the new Inverted Y. In this example, the new Inverted Y is also
before the X. So, not only is it reordered, but, also inverted. Tricky, eh?
:)

Enjoy!


Best regards,
Fred, N7FMH

PS. The VFR (and IFR) tiles are interesting. Any link to them will require
updating since they do change as the FAA sees fit. The last update was in
February 2012.



-----Original Message-----
From: xastir-bounces at lists.xastir.org
[mailto:xastir-bounces at lists.xastir.org] On Behalf Of Tom Hayward
Sent: Monday, March 19, 2012 14:00
To: Xastir - APRS client software discussion
Subject: Re: [Xastir] US Topo GeoPDF?

On Mon, Mar 19, 2012 at 10:52, Tom Hayward <esarfl at gmail.com> wrote:
> On Mon, Mar 19, 2012 at 10:51, Tom Hayward <esarfl at gmail.com> wrote:
>> Alternatively, you can get seamless USGS Topo tiles from an ESRI tile 
>> server. Looking at the license, I think it would be fully compatible 
>> with Xastir as long as we don't exceed the transaction limit. The 
>> tile format is Google/Bing--is this the same as OSM/Mapnik?
>
> Oops, forgot the link:
>
> http://www.arcgis.com/home/item.html?id=99cd5fbd98934028802b4f797c4b17
> 32

I'm not sure whether to call this a success or a failure, but I got the ESRI
topo tiles to display in Xastir using the OSM tile feature.
Unfortunately the tiles aren't numbered with the same scheme:

http://i.imgur.com/ie4g4.jpg

If you want to try this yourself, just duplicate one of the OSM*.geo files
and change the URL to:

http://server.arcgisonline.com/ArcGIS/rest/services/USA_Topo_Maps/MapServer/
tile/


This may be the "inverted Y" Fred mentioned. Is there a way to configure
this in the OSM*.geo file, or would I need to add this to the OSM render
code?


Tom KD7LXL
_______________________________________________
Xastir mailing list
Xastir at lists.xastir.org
http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir