Oil Platform Location Suitability using WMS

Introduction

The goal of this project is to visualize and consider the various contributing factors which can influence the decisions of the stakeholders involved in the continuation of oil extraction along Canada’s Atlantic coast using web mapping services and publicly available data. These stakeholders have expressed interest in incorporating open data exchange standards and open source software for the realization of this goal. Web mapping services (WMS) and freely available have the potential to serve as a valuable source of geospatial contents and services which can be utilized in practical business applications to provide economically feasible alternatives to managing and analyzing spatial information. When dealing with hydrographic data associated with offshore oil exploration current uses and constraints which characterize the region may affect the potential for the designation of a suitable site for the oil platform to be built. This project is designed to illustrate the proximity of these features to suitable site locations for oil platforms. For the purposes of this project I have used two features marine protected areas and ferry routes which are used in my analysis. These features can be considered as examples of constraints which can be imposed on decision makers when selecting a suitable location for the development of an oil platform. The methods employed in this tutorial outline the necessary steps involved in making use of freely available data and open source software in order to generate effective maps concerning the goals of the stakeholders involved in the implementation of offshore oil platforms.

Objectives

1. Utilizing web mapping services and freely available data in order to facilitate decision making involved with offshore oil exploration in Atlantic Canada.

2. Visualize site suitability for the implementation of an offshore oil platform taking into account the constraints or variables which must be considered when deciding on a suitable location.

Methods

GIS Software

Quantum GIS and GRASS

Quantum GIS is a free open source Geographic Information System (GIS) package that supports a number of different geospatial vector and raster file types and database formats. A detailed description of the utilities and applications offered by this free and open source software can be viewed as well as downloaded at [1]. The version of QGIS utilized in this project 1.5.0 ‘Tethys’ acts as a Graphical User Interface supported by the GIS functionalities and applications of Geographic Resource Analysis Support System (GRASS). The capabilities of GRASS allow it to process and analyze; imagery, raster data, and topological vector data.

FW Tools

The GDAL/OGR libraries are a set of command line utilities for reading and writing geospatial raster and vector format data. They are included in the FW Tools open source programs for GIS applications. This can be downloaded at: [2]

Data

WMS

A variety of WMS were used to incorporate the number of different features of spatial information which must be considered when implementing a project of this magnitude. Raster images generated by these services were combined in order to amalgamate the most relative layers of spatial information that were necessary to facilitate the decision making process. Some of the WMS layers that were overlaid from different servers for the visualization of regional features included:

- Bathymetry

- Depth Contours

- Federal and Provincial Protected Areas

- Transportation Network

- Political Boundaries

Working with GRASS and Quantum GIS

Retrieving data from WMS Servers

In Quantum GIS the raster images utilized in this project were retrieved by invoking the server URL from a number of different sources depending on the availability of spatial information provided by each service. An example of a get capabilities request to display the general information about the WMS and specific information about the available map layers which was used is: >http://atlas.gc.ca/cgi-bin/atlaswms_en?VERSION=1.1.1&request=Getcapabilities&service=wms< When opened in a web browser this request returns the specific information pertaining to the WMS including the title, abstract of what is offered by this service, contact information, the source of the data and the formats offered. Quantum GIS version 1.5.0 ‘Tethys’ can act as a WMS client that understands WMS 1.1, 1.1.1, and 1.3 servers.

The following steps describe the necessary procedure involved to retrieve data provided by WMS servers using the Quantum GIS Graphical User Interface (GUI).

1. In the Quantum GIS GUI click on the “Layer” tab and select “Add WMS layer” (or the shortcut for this is “Ctrl+Shift+W”).

2. Select “New”, this will prompt you to create a new WMS connection. In the connection details create a name which you wish to call each service. Copy and paste the URL to access the WMS server. i.e. http://atlas.gc.ca/cgi-bin/atlaswms_en -Note sometimes the WMS will require basic authentication, in this case a user name and password must be entered. Click “OK”. The server has now been added to your list of possible connections.

3. Click “Connect”, the raster layers offered by the service will be listed and organized by “ID”, “Name”, “Title”, and “Abstract”. This will help you to distinguish between the different layers and select the appropriate ones to add to your map.

4. “Image Encoding” - lists the possible formats that are supported by both the client (Quantum GIS) and the server. Depending on what formats are supported image formats typically include: PNG, PNG24, JPEG, GIF and TIFF formats. PNG and GIF formats support image transparency while JPEG does not support this capability.

Note – “You will typically find that a WMS server offers you the choice of JPEG or PNG image encoding. JPEG is a glossy compression format, whereas PNG faithfully reproduces the raw raster data. Use JPEG if you expect the WMS data to be photographic in nature and/or you don’t mind some loss in picture quality. This trade-off typically reduces by 5 times the data transfer requirement compared to PNG. Use PNG if you want precise representations of the original data, and you don’t mind the increased data transfer requirements”. (QGIS, 2010)

5. “Options” – Create a name which you wish to call the single layer which you have selected or the multiple layers to be combined in one output image.

6. “Coordinate Reference System” (CRS) – Will list the number of different CRSs supported by the server and allow you to select one of them. Depending on the capabilities of the server, WMS layers can be displayed in a number of different CRSs. In order to facilitate the alignment of WMS layers choose a common one that is supported by all of your servers (if more than one is being used). To define a new CRS for the layer/layers being added to the map click on the “Change” icon to select from a predefined list of supported CRSs. Once you have selected your desired CRS click “OK”. Note – If you already know the CRS you would like to use, you can quickly find it using the “Search” bar.

7. Now the layer, image format and CRS have been selected, click “Add” to add the layer/layers to your new map.