OGC Web Processing Service


This section should be usable for any WPS implementation and should give you general picture about the OGC WPS standard.

Open Geospatial Consortium
is a non-profit, international, voluntary consensus standards organization that is leading the development of standards for geospatial and location based services.

In short: it defines standards for geo-people, to communicate in the Internet environment.

One of the standards, defined by OGC is Web Processing Service:

... provides rules for standardizing how inputs and outputs (requests and responses) for geospatial processing services, such as polygon overlay. The standard also defines how a client can request the execution of a process, and how the output from the process is handled. It defines an interface that facilitates the publishing of geospatial processes and clients’ discovery of and binding to those processes. The data required by the WPS can be delivered across a network or they can be available at the server.

Again in short: the standard describes, how to execute some geospatial analysis deployed on the server and obtain the result back.


Before you start to deal with PyWPS, consider to have a look at the standard - you can download it for free.

Invoking WPS server

You can invoke WPS server in two ways: using HTTP GET method with key-value-pairs encoded request, or HTTP POST method, using XML format of the request. They are both described well in the standard.

KVP request encoding

In general, parameters are formated in the form:


They are written usually behind ? sign of the server address. For example, invoking GetCapabilites operation, see GetCapabilities

Let’s look at this URL more detaily:

It is the protocol of the request. We are using Hyper Text Transfer Protocol
The WPS server address, where you will install it. This is usually something like google.com, microsoft.com, gnu.org or similar. At the beginning, it will be mostly localhost, which means, that it will be your computer.
Path name of the installed PyWPS server.
The ? sign indicates, that the request parameters will start

The KVP-encoded request. We send two request parameters to the server:

  • service - which we set to WPS
  • request - which is set to GetCapabilities

The parameter names should be case insensitive, means, that SERVICE is the same as service and the same as SeRvIcE. The parameter values should be mostly case insensitive as well, means GETCAPABILITIES should be the same as getcapabilities and GetCapabilities.

XML request encoding

In this case, the request is encoded in XML form and send to the server directly via HTTP POST (the WPS server will read the file from standard input directly).


Since XMLs are maybe too complicated, we will be using KVP encoding in this tutorial. Only one XML-encoded request type example will be showed. There are examples in the test directory of PYWPS as well as in the WPS Standard document.

GetCapabilities request in XML form would look like:

<?xml version="1.0" encoding="UTF-8"?>
<ows:GetCapabilities xmlns:ows="http://www.opengis.net/ows/1.1" xmlns:wps="http://www.opengis.net/wps/1.0.0" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.opengis.net/ows/1.1 ..\wpsGetCapabilities_request.xsd" language="en" service="WPS">

Other requests can be much more complicated.

WPS Request types

Similar to other OGC Web Services (such as WMS, WFS or WCS), WPS has three basic request types. Namely GetCapabilities, DescribeProcess and Execute.



Mandatory parameters:

service request

The server returns basic Capabilities document. Among others it contains:

  • Title
  • Abstract
  • Keywords
  • Service provider (Name, Organization, Address, ...)

OperationsMetadata - URLs to particular operations (GetCapabilities, DescribeProcess and Execute)

ProcessOfferings - List of available processes




New mandatory parameters appeared in the request URL:

  • WPS version number
  • Process identifier - it can be process identifier as stated in the Capabilites document or key word ‘all’ for all process descriptions

The ProcessDescriptions document contains detailed description of selected processes. Each process is identified by

  • Title
  • Identifier
  • Abstract (optional)
  • DataInputs
  • DataOutputs

Now the client can be configured in order to be able to Execute the process.




No new mandatory parameters appeared in the request URL, however, several optional did, among others DataInputs, but we will discuss some of them later.

Most important parameter, DataInputs is encoded as again as key-value-pairs, separated with ; sign.

WPS In- and Outputs

Three types of inputs and outputs are defined in the OGC standard. LiteralData, ComplexData and BoundingBox data.


LiteralData can be any character string of special type, as described in http://www.w3.org/TR/xmlschema-2/

In PyWPS, there is currently support for
  • String
  • Float
  • Integer
  • Boolean


This data type is used for pasting complex - Vector- Raster- or other data to the server or obtain it as result of the process. There are two ways, how this complex data are handled,

  • Either you send them directly as part of the request to the server or you obtain them as part of the XML response from the server. This is mostly done by vector data, using GML or other text-based format. For raster data, they can be encoded using base64 encoding
  • Or you send or obtain just reference to the data – URL to the file or service, where the data can be downloaded.


If you need to define or obtain some kind of bounding box (2 or more dimensional), you can use this type of data.


Now you should be able to understand, what WPS is about, which are the in- and outputs, get some image how to call each request type and what you can expect as result. Let’s continue with PyWPS.