(PTV Mercator)
(SmartUnits)
PTV xMap server is capable to address the map section that is to be rendered with double precision. The requested rectangle is transformed by the server into a SmartUnit based center coordinate and a scale value which are then passed to gpRenderer in float typed variables. Only minor inaccuracies apply at this stage; this means that xMap server is capable to deliver images with accurate tile borders given a x/y/z tile coordinate.
The tile borders are accurate - nevertheless there are some rendering issues in the tile images for zoom levels > 19 mainly caused by clipping / buffering problems in the gpRenderer itself. Using the map for background information only, one is able to work with the map nonetheless.
The maximum (integer) value for the zoom level calculates to 22 or 22.95 if the zoom is a real number. This is due to the fact that the minimum scale value in gpRenderer is defined to be 0.004 SmartUnits per pixel and zoom level 23 calculates to a slightly lower value, 0.003876 SmartUnits per pixel. One could ignore this and work with level 23 by rendering the map section wise instead of tile wise to avoid offsets when joining the tiles. Nevertheless, one would have to take into consideration that there could be inaccuracies when digitising objects on the map.
The following table lists the scale values for the different zoom levels.
| Zoom Level (Google Tiling Scheme) | Sample | Tile Width (PTV Mercator) |
Tile Width (SmartUnits) |
xMap Scale ((SmartUnits per Pixel)*100) |
|---|---|---|---|---|
| 0 |
|
40030173.592041 | 8323072.190443 | 3251200.074391906 |
| 1 |
|
20015086.796021 | 4161536.095222 | 1625600.037195953 |
| 2 |
|
10007543.398010 | 2080768.047611 | 812800.0185979765 |
| 3 |
|
5003771.699005 | 1040384.023805 | 406400.00929898827 |
| 4 |
|
2501885.849503 | 520192.011903 | 203200.00464949413 |
| 5 |
|
1250942.924751 | 260096.005951 | 101600.00232474707 |
| 6 |
|
625471.462376 | 130048.002976 | 50800.00116237353 |
| 7 |
|
312735.731188 | 65024.001488 | 25400.000581186767 |
| 8 |
|
156367.865594 | 32512.000744 | 12700.000290593383 |
| 9 |
|
78183.932797 | 16256.000372 | 6350.000145296692 |
| 10 |
|
39091.966398 | 8128.000186 | 3175.000072648346 |
| 11 |
|
19545.983199 | 4064.000093 | 1587.500036324173 |
| 12 |
|
9772.991600 | 2032.000046 | 793.7500181620865 |
| 13 |
|
4886.495800 | 1016.000023 | 396.87500908104323 |
| 14 |
|
2443.247900 | 508.000012 | 198.43750454052162 |
| 15 |
|
1221.623950 | 254.000006 | 99.21875227026081 |
| 16 |
|
610.811975 | 127.000003 | 49.609376135130404 |
| 17 |
|
305.405987 | 63.500001 | 24.804688067565202 |
| 18 |
|
152.702994 | 31.750001 | 12.402344033782601 |
| 19 |
|
76.351497 | 15.875000 | 6.2011720168913005 |
| 20 |
|
38.175748 | 7.937500 | 3.1005860084456502 |
| 21 |
|
19.087874 | 3.968750 | 1.5502930042228251 |
| 22 |
|
9.543937 | 1.984375 | 0.7751465021114126 |
| 23 |
|
4.771969 | 0.992188 | 0.3875732510557063 |
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