PyWPS Quickstart

PyWPS is an OGC WPS (Web Processing Service 1.0.0) server implementation written in Python.

PyWPS is installed by default on OSGeo-Live. This Quickstart describes how to:

• test the PyWPS installation
• configure the PyWPS instance
• create and deploy processes in PyWPS
• perform GetCapabilities, DescribeProcess and Execute operations

Contents

• PyWPS Quickstart
  • Tester Application
  • Configuration
    • Processes
  • Things to Try
  • What’s Next

Tester Application

To run the PyWPS tester, use the PyWPS launcher from the Web Services group. This opens Firefox displaying http://localhost/pywps/wps.py?service=WPS&version=1.0.0&request=GetCapabilities. The XML response provides an overview of the Service (title, abstract, keywords), the Service point of contact as well as a list of processes supported by the PyWPS installation.

Lets select the ultamitequestionprocess process from the list and display its description by calling the DescribeProcess operation. In Firefox, enter the following URL: http://localhost/pywps/wps.py?service=WPS&version=1.0.0&request=DescribeProcess&identifier=ultimatequestionprocess

You should see WPS DescribeProcess response document. The XML response provides a description of what the process does as well as specifics (name, type) on the inputs and outputs. We can see in the above response that the ultimatequestionprocess process (according to its description) is able to provide the Answer to Life, the Universe and Everything, takes no inputs and provides a single integer output.

Now let’s run the ultimatequestionprocess process on the server. In Firefox, enter the following URL: http://localhost/pywps/wps.py?service=WPS&version=1.0.0&request=Execute&identifier=ultimatequestionprocess

Here we can see the answer to life, universe and everyting is 42.

Configuration

You can configure the PyWPS instance in the /etc/pywps/pywps-wsgi.cfg configuration file. More information on the configuration option can be found in the standard documentation

Processes

You can find some more example processes in the /etc/pywps/processes directory. Every process is usually stored in separate file and is represented by a Python class, with constructor and execute() methods:

# Example of PyWPS process (shorten)
from pywps.Process import WPSProcess
class Process(WPSProcess):
 def __init__(self):
     WPSProcess.__init__(self,
                         identifier="ultimatequestionprocess",  # the same as the file name
                         ....

 def execute(self):
     import time
     self.status.set("Preparing....", 0)
     for i in xrange(1, 11):
         time.sleep(2)
         self.status.set("Thinking.....", i*10)
     # final answer
     self.Answer.setValue("42")

Directory of your process deployment is configured within the PYWPS_PROCESSES environment variable.

Things to Try

Here are some additional challenges for you to try:

1. Try updating some of the configuration values to see how they are updated in the GetCapabilities requess
2. Try running the DescribeProcess and Execute requests against other processes

What’s Next

PyWPS gives you the freedom and flexibility to write your own Python processes and expose them accordingly.

• Official documentation

  For further information on PyWPS configuration and the API, consult the documentation on the PyWPS website.

• Tutorial

  Try out the course, which includes setting up an OpenLayers based web client.