| TileStache.Sandwich | index |
Layered, composite rendering for TileStache.
The Sandwich Provider supplies a Photoshop-like rendering pipeline, making it
possible to use the output of other configured tile layers as layers or masks
to create a combined output. Sandwich is modeled on Lars Ahlzen's TopOSM.
The external "Blit" library is required by Sandwich, and can be installed
via Pip, easy_install, or directly from Github:
https://github.com/migurski/Blit
The "stack" configuration parameter describes a layer or stack of layers that
can be combined to create output. A simple stack that merely outputs a single
color orange tile looks like this:
{"color" "#ff9900"}
Other layers in the current TileStache configuration can be reference by name,
as in this example stack that simply echoes another layer:
{"src": "layer-name"}
Bitmap images can also be referenced by local filename or URL, and will be
tiled seamlessly, assuming 256x256 parent tiles:
{"src": "image.png"}
{"src": "http://example.com/image.png"}
Layers can be limited to appear at certain zoom levels, given either as a range
or as a single number:
{"src": "layer-name", "zoom": "12"}
{"src": "layer-name", "zoom": "12-18"}
Layers can also be used as masks, as in this example that uses one layer
to mask another layer:
{"mask": "layer-name", "src": "other-layer"}
Many combinations of "src", "mask", and "color" can be used together, but it's
an error to provide all three.
Layers can be combined through the use of opacity and blend modes. Opacity is
specified as a value from 0.0-1.0, and blend mode is specified as a string.
This example layer is blended using the "hard light" mode at 50% opacity:
{"src": "hillshading", "mode": "hard light", "opacity": 0.5}
Currently-supported blend modes include "screen", "add", "multiply", "subtract",
"linear light", and "hard light".
Layers can also be affected by adjustments. Adjustments are specified as an
array of names and parameters. This example layer has been slightly darkened
using the "curves" adjustment, moving the input value of 181 (light gray)
to 50% gray while leaving black and white alone:
{"src": "hillshading", "adjustments": [ ["curves", [0, 181, 255]] ]}
Available adjustments:
"threshold" - Blit.adjustments.threshold()
"curves" - Blit.adjustments.curves()
"curves2" - Blit.adjustments.curves2()
See detailed information about adjustments in Blit documentation:
https://github.com/migurski/Blit#readme
Finally, the stacking feature allows layers to combined in more complex ways.
This example stack combines a background color and foreground layer:
[
{"color": "#ff9900"},
{"src": "layer-name"}
]
A complete example configuration might look like this:
{
"cache":
{
"name": "Test"
},
"layers":
{
"base":
{
"provider": {"name": "mapnik", "mapfile": "mapnik-base.xml"}
},
"halos":
{
"provider": {"name": "mapnik", "mapfile": "mapnik-halos.xml"},
"metatile": {"buffer": 128}
},
"outlines":
{
"provider": {"name": "mapnik", "mapfile": "mapnik-outlines.xml"},
"metatile": {"buffer": 16}
},
"streets":
{
"provider": {"name": "mapnik", "mapfile": "mapnik-streets.xml"},
"metatile": {"buffer": 128}
},
"sandwiches":
{
"provider":
{
"name": "Sandwich",
"stack":
[
{"src": "base"},
{"src": "outlines", "mask": "halos"},
{"src": "streets"}
]
}
}
}
}
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