Terraserver: Tiles Vs OpenGIS Web Map Server
Starting with TerraServer tile:
- X=204
- Y=2932
- Z=19N
- S=13 (8m)
Using this python snippet:
TILE_PX = 200
def terra2utm(x, y, z, s):
x = x * TILE_PX * math.pow(2, s-10)
y = y * TILE_PX * math.pow(2, s-10)
return x, y
The extent of the tile can be computed:
uL = terra2utm(204, 2933, "19N", 13)
lR = terra2utm(205, 2932, "19N", 13)
Which gives:
- uL = 326400, 4692800
- lR = 328000, 4691200
That then converts to (in WGS-84):
- uL = 42.36810, -71.10832
- lR = 42.35405, -71.08843
Now we can compare the tile to the WMS version:
| Tile | WMS |
 |
 |
Close, but a bit distorted. Bringing the WMS image up in the Terra-Map Server web interface shows that we ended
up with the wrong resolution. (Width Resolution (m/px): 8.3850 Height Resolution (m/px): 7.5952)
Where did I go wrong?
(19:37) [/Maps/Services]
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New Features
Some new features to the GNIKville mapper:
- New theme: Tiger
street level maps (try it)
- Overview map, also using the Tiger service.
(12:27) [/Maps/Services/mapper]
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Mapping at GNIKville
So last night I created a new little mapping
service. It uses the TerraServer for the images
and is inspired by, and inferior to, the ACME Mapper. But, next I'm going
to add support for drawing GPS trails and linking to GPS-tagged
digital pictures. Then it might just be something...
Update: I've added photos! Check out our walk
into Boston. I've got code to draw trails as well, but right now
gnik.com doesn't have the Python interface to the GD graphics library...
(17:59) [/Maps/Services]
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