[Xastir] US Topo GeoPDF?

[Fred Hillhouse]

>> With the correct decoding, the SlippyTiles can be accessed from the
National Map.

> Are you suggesting adding National Map support to Xastir, similar to the
online osm tiles feature? If we are lucky, maybe the tile specs are the
same! I don't think the USGS wants their tiles being used with other
services, but I haven't asked.

You are not so lucky about the tile spec. From Wireshark, the request looks
like this:
[truncated] GET
/ArcGIS/rest/services/DRG/TNM_Digital_Raster_Graphics/MapServer/export?dpi=9
6&format=png&bbox=-7871179.42469431%2C5320017.16864827%2C-7868733.43978918%2
C5317571.18374314&bboxSR=102113&imageSR=102113&size=1024%2C1024&f=image

I looked briefly at how to specify the bounding box (bbox):
http://help.arcgis.com/en/arcgisonline/content/index.html#//011q000000020000
00

I will have to play around now myself. It shouldn't be difficult to master.
Personally, I use 256x256 tiles and save them in the same way the OSM tiles
would be saved (Z/X/Y.png). I am using APRSIS32. For Xastir, if a different
map size is needed, then the bounding box could cover a whole area. I
actually tapped the USGS maps and generate tiles using bounding boxes for
use in APRSIS32. I like them better than the CycleMap tiles from OSM.

This is Slippy map:
http://wiki.openstreetmap.org/wiki/Slippy_map_tilenames

National Map was added to ExpertGPS/Win32 recently which I have been using
for 10+ years. It appears he watches the licensing closely. It would be wise
since his product is commercial.

>From a license aspect, I have looked through the license and concluded that
for my no-commercial use, I would be okay to download the map. I am not a
lawyer so my interpretation might be flawed. 

> 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?

Yes, Google and Bing and many others use this format. It appears to have
become the standard web display. Some servers do a "invert Y" and the same
basic format. I say same basic format because the X and Y may be reversed in
a web address or other little items are added, such as x=## rather than just
x. [For the curious: Inverted Y = (2^Z-1)-Y. I found aeronautical/nautical
charts that use this.]

As an aside, I save all my tiles on the hard drive. My station is mobile
without an internet connection. For areas I play in, I have gathered
appropriate tiles. The obvious benefit is I always have a map.


Best regards,
Fred, N7FMH