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3.2 Framework of the WebGIS application

The framework of the application was based upon the OpenGeo 'Geostack' (Figure 11).

Figure 11

Figure 11: Open source 'Geostack' used by project (after OpenGeo 2012. Image: © Boundless 2013).

This modular, layered design comprises database, application server and user interface, using in this instance the following software:

All software is open source and details of how to obtain the software is provided (Appendix 1).

Module 1: database

The database design essentially comprises two components, spatial (coordinates) and descriptive (attributes). Vector data is contained within a PostgreSQL 9.1 and PostGIS 2.0 database as a simple spatial table with attributes comprising the various columns within the table as a geometry collection (Figure 12 and Table 2).

Figure 12

Figure 12: Screenshot illustrating spatial database structure.

Table 2: Table of database fields
Database field Description
GID (PK) Unique identifier and primary key
Name Name of feature
Feature description Textual field to allow user to describe feature
Period Date to which feature may belong
Geom Geometry of point, line or polygon
Source Allows user to indicate which visualisation method or methods shows feature
Value Field that allows the relative value of the heritage feature to be assessed and conveyed by user-assigned numerical value 1-10
Recorded by Name of user who has transcribed feature

To facilitate data collection that can contribute to Objective 7, attribute data field 'source' allows the user to indicate the visualisation method/s that show the features.

Module 2: application server

GeoServer, an open-source web map server, was used to house and serve data. Communication between PostGIS and GeoServer was achieved via structured query language (SQL). This allows transactions using the Web Feature Service (WFS-T) Standard 1.0.0, which allows the user, via a client interface, to modify the spatial data held within the PostGIS database. The primary reason for choosing GeoServer rather than an alternative open-source solution, such as MapServer, was the native ability to support WFS-T. MapServer does not support WFS-T and requires an additional program to be installed, known as TinyOWS, to implement WFS-T functionality. GeoServer also possesses a significantly more intuitive admin interface than MapServer, reducing the learning curve required to use the software effectively (Figure 13).

Figure 13

Figure 13: Example of GeoServer administration interface.

Raster images of LIDAR data were pre-seeded using GeoWebCache, which is incorporated into GeoServer, to speed up tile generation performance and enhance user experience. Given the large extent of the study area, PCA and hillshaded raster bit depth was kept to 8bit to minimise tile generation and layer load times. The images were served via Web Map Server (WMS) 1.1.1 service.

Module 3: user interface

The application runtime location was client side within a web browser via JavaScript embedded within a HTML page. Application coding methods use a combination of open source OpenLayers, and GeoExt, which is based upon ExtJS JavaScript library. The full JavaScript code for the application is included in Appendix 2.


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