A tile-on-demand tile server built with PIL and Tornado
A tile-on-demand tile server built with PIL and Tornado.
We want to store a high-resolution image in memory on the server as a numpy array. Then when a client requests a particular tile, we can make the PNG of the requested tile by slicing the numpy array and using PIL to write the resulting PNG back to the client through a StringIO stream.
This is primarily intended for building interactive visualizations in research settings where we might want to skip the time- and/or disk-intensive tile generation step required by typical tile servers.
$ pip install projectile
Serve a test image from the USC-SIPI Image Database:
$ projectile sanfran
Manually request a particular tile by navigating to http://localhost:8000/2/1/2.png.
Try zooming and panning in the demo client by navigating to http://localhost:8000/.
Serve one of your own images (any format readable by PIL) with
$ projectile some_image.tiff
or, if you have data in a numpy
$ projectile some_image.npy
Load an image in grayscale mode and apply a colormap:
$ projectile --mode L --cmap viridis pentagon
To test the performance limits of on-demand tiling, download this high resolution map of Great Britain (8,150 × 13,086 pixels, file size: 102.74 MB) from Wikimedia Commons.
Grayscale performance test:
$ projectile britain.jpg -m L
Reducing tile resolution when running in color:
$ projectile britain.jpg --tile_size 128
The server will serve grayscale and RGB images in their original colors at
<z> is the zoom level,
<y> specify the coordinates of the
tile at that zoom level (
0/0 is the top left tile), and
<s> specifies the
image tile resolution in pixels (must be a power of 2).
The server will serve colormapped versions of a grayscale image at
<cmap> is the name of a matplotlib colormap, and
specify the range of image pixel values linearly interpolate against the
colormap (pixel values outside this range will be clipped).
Using a custom client
If you like the projectile backend but just want to use a simple custom client
contained in a single HTML file
custom_client.html, you can run
$ projectile array.npy --client custom_client.html
to make projectile serve your client instead of the included demo client.
Using projectile in your existing Tornado web application
The core functionality is exposed in the
TileHandler class defined in
server.py, which you can use in your own Tornado web
from tornado import web from projectile.server import TileHandler ... app = web.Application([ (r'/([0-9]+)/([0-9]+)/([0-9]+)/([0-9]+).png', TileHandler, dict(array=array)), ... ]) ...
Launching projectile from your own Python code
You can also launch a server from your own Python code with the
defined in server.py:
from projectile.server import run run(array)
The demo client is lifted from http://bl.ocks.org/mbostock/5914438, with the addition of a small filtering check to prevent the client from requesting tiles which lie beyond the image boundaries.
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