A GIS-based Web Application

27 Jul 2013 - by @黄野

Youtube

Youku (China)

1. Background

This demo belongs to one of my practical experiments by which I try to create a GIS-based mockup from beginning to end.

To develop a GIS-based application, we have to follow a specific workflow listed as following:

Collecting, manipulating and managing the spatial data
Building Models for the GIS analysis
Executing the analysis based on data and models
Visualizing computational results of the analysis
Sharing results with users

In this project, tasks mentioned above can be separately assigned to a set of GIS-related softwares listed below:

Applying desktop softwares, such as ArcGIS or QGIS for data manipulation
Working with GeoServer for publishing and managing the spatial data and GIS analysis models
Using Pysal and Matplotlib for testing the implementation of GIS models and employing some WPS free sources, such as GeoServer Python Extension, Zoo Project, PyWPS or 52north to compile models
Using OpenStreetMap-based services, such as OpenLayers, MapBox, MapQuest or Leaflet, to build the front-end interface.

2. Introduction

This web application is mainly focused on implementing one concept from GIS called Web Processing Service. Generally, you can use this app to:

Execute fundamental GIS-based tasks by executing 183 basic WPS analysis modules, such as buffer, area, boundary, centroid, contains, convexHull, crosses, densify, difference, disjoint, intersection, intersects, touches, simplify, reproject, splitPolygon, union, within and so on.
Execute more complicated tasks by executing another 4 different kinds of WPS analysis modules, “py:BufferSplit”, “py:SCBI”, “py:Simplify and ConvexHull” and “py:disbear”, respectively.
Edit (draw points/lines/polygons or delete input/output features) the Vector Layer and the Result Layer.
Locate any place that you would like to check. You can locate the place by either inputting the text addresses or inputting the coordinates of that place.
View the attributes’ values of the WMS map layers.

An important advantage of using this application is the low cost of learning for people to implement the GIS WPS analysis models. The traditional GIS desktop softwares are too much demands for specialized knowledge of GIS because of the complicated interactive operations between machines and users and the tedious workflows from data management to data visualization. This application provides a easy way for people to enhance their decision-making abilities. Just open up your browser, you can explore the spatial relationships between objects based on a map.

3. Prerequisites

Optional tools include:

4. How to deploy a GIS-based application by Geoserver and Tomcat?

Install Apache HTTP Server 2.2
Install Apache Tomcat 6.0
Install Geoserver on Apache Tomcat Server
Deploy Geoserver WPS plugins(If you need)
- Download Geoserver WPS extension
- Extract files to the geoserver/WEB-INF/lib
- restart the Apache Tomcat 6.0
Install Python Scripting Extension of Geoserver(If you need)
- Place the Python Scripting Extension of Geoserver in the directory geoserver\WEB-INF\lib and restart the Apache Tomcat 6.0. You will find that a new folder named “scripts” is created in the directory geoserver\data. Place the WPS python files in the directory geoserver\data\scripts\wps. You can also customize your own WPS modules by writing this sort of python scripts. Just place the python file in this directory and the WPS builder of Geoserver will automatically connect them with our web application. All the python WPS modules will be shown on the list with the name py:XXXX.
Configure the proxy.cgi parameters in order to solve the Browser Cross Domain problem
- Create a new folder named “cgi” in the directory geoserver\WEB-INF and place the OpenLayers proxy.cgi in it. Open the proxy.cgi and add a new array value localhost:8080 in the array allowedHosts. Find a XML file named “web.xml” in the directory geoserver\WEB-INF and add codes shown as following:

<servlet>
    <servlet-name>cgi</servlet-name>
    <servlet-class>org.apache.catalina.servlets.CGIServlet</servlet-class>

    <init-param>
        <param-name>debug</param-name>
        <param-value>0</param-value>
    </init-param>
    <init-param>
        <param-name>cgiPathPrefix</param-name>
        <param-value>WEB-INF/cgi</param-value>
    </init-param>
    <init-param>
        <param-name>executable</param-name>
        <param-value>c:/Python27/python.exe</param-value>
    </init-param>
    <init-param>
        <param-name>passShellEnvironment</param-name>
        <param-value>true</param-value>
    </init-param>

    <load-on-startup>5</load-on-startup>
</servlet>
    
<!-- The mapping for the default servlet -->
<servlet-mapping>
    <servlet-name>default</servlet-name>
    <url-pattern>/</url-pattern>    
</servlet-mapping>

<servlet-mapping>
    <servlet-name>cgi</servlet-name>
    <url-pattern>/cgi/*</url-pattern>
</servlet-mapping>

Publish a Shapefile
Run and test the application Place the application codes package in the directory geoserver/data/www. Restart your Apache Tomcat Service and click the link shown as following to test whether the application is successfully deployed or not (For example: http://localhost:8080/geoserver/www/yourapp.html). It will take a few minutes when you restart the Tomcat and reload the application.