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 software 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, for 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. Utilize 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.
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, and the software can be 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]
WMS Data
A variety of WMS servers 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
- Ferry Routes
- Political Boundaries
To illustrate my study area as well as some of the web map services utilized in this project, an image of my study area can be seen below including the features listed above. The get map requests employed to generate this image included:
Bathymetry - http://bluefin.mar.dfo-mpo.gc.ca/wmsconnector/com.esri.wsit.WMSServlet/bathy_atlantic
Depth Contours - http://geonetwork3.fao.org/ows/31632
Atlas of Canada WMS - http://atlas.gc.ca/cgi-bin/atlaswms_en
Methods
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 server 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.
The graphical user interface utilized in QGIS to facilitate this process can be seen below:
Reprojecting Vector Files
The WMS raster images used in this project can be displayed in a number of pre-defined European Petroleum Survey Group (EPSG) projections. The vector files which will be used for analysis in GRASS were derived from requests for data from different online sources. These vector files come with default projections which do not always align with the projections offered by the WMS. In this case we must redefine the projections so the vectors can be overlaid on the WMS raster in order to visualize the results of our GRASS analysis. The vector file containing Canada’s terrestrial and marine protected areas came with a default projection (Canada Lambert Conformal Conic) which was not recognized as a supported projection by the WMS and as a result could not be overlaid on the WMS layers. In order to address this issue the vector needs to be reprojected. “The OGR Simple Features Library is a C++ open source library (and commandline tools) providing read (and sometimes write) access to a variety of vector file formats including ESRI Shapefiles” (OGR, 2010). The capabilities of this library were utilized with the FWTools shell in order to reproject the protected areas vector file so that it may be overlaid on the WMS layers. The command to perform this operation is as follows:
D:\ > CARTS.shp –t_srs “EPSG:4269” carts_20101010.shp
Where “D:\” is the shell prompt showing the directory where the files are located (i.e. don't type that part, but you will need to use the "cd" command to change to the proper directory before running the command), “CARTS.shp” is the name of the shapefile which is being reprojected, “-t_srs” refers to spatial reference system, ‘”EPSG:4269”’ designates the new EPSG projection (in this case, NAD83 lat,long) which will be applied to the current shapefile, and “carts_20101010.shp” is the name of the shapefile being reprojected. Now that the vector has been reprojected it can now be overlaid on the existing WMS layers and used in GRASS.
Setting up a GRASS database in Quantum GIS
In the QuantumGIS GUI click on the “New Mapset” icon, this will prompt you to setting up a GRASS database which stores the data which is generated and used in the analysis. The steps to setting up a GRASS database are as follows:
1. Select an existing directory or create a new one in which all of your data will be accessed and maintained. Click | ->Next
2. Select a location or set up a new location where the collection of maps will be stored for a project. Click | -> Next
3. The “PROJECTION” step will allow you to define the projection to be used in GRASS. Click | -> Next
4. Defining the GRASS region, in this step you are able to define the workspace in which the area you will be conducting analysis on can be set. The region can either be manually defined by entering the bounding coordinates for your project, or the “Set current QGIS extent” icon will set the GRASS region to the current extent which you are viewing in the Quantum GIS GUI. | Next ->
5. Enter a new mapset name, this step allows you to name the collection of maps that are created in GRASS. Click | -> Next
6. This final step prompts you to the paths you created in GRASS database. Click | -> Finish, you have created your GRASS database. Notice the GRASS tools icon has been made accessible allowing you to use the wealth of modules available in GRASS.
Import loaded vectors into the GRASS database
To conduct spatial analysis in GRASS using the vector files we must first import the vectors into the GRASS database. In GRASS tools, select the ‘Import Loaded Vector - v.in.ogr.qgis'[3] module. This step will import the vector files into the GRASS database, which can then be used for analysis in GRASS.
Import Ferry Routes into GRASS:
v.in.ogr -o dsn=D:/Student/100***/FinalProj/route.shp output=FerryRoute
Import Protected Areas:
v.in.ogr -o -e dsn=D:/Student/100***/FinalProj/ Proproj.shp output=ProtectArea
Where “route.shp” and “Proproj.shp” are the reprojected vector files and “output=” defines the names of the newly created files which have been imported into the GRASS database.
Buffer Areas and Lines in GRASS
In order to prevent the possibility of constructing the oil platform within a relatively close proximity to federal and provincial protected areas or the ferry routes a buffer is conducted on these features using GRASS tools. The federal and provincial protected areas and ferry routes are used in this tutorial to demonstrate the capabilities of using GRASS tools to conduct spatial analysis on geographical features. The steps listed below show how to create a buffer around features using GRASS and to display the results in Quantum GIS.
1. Once a GRASS database has been created the GRASS tools can be accessed by either navigating to the “Plugins” tab -> GRASS -> Open Grass Tools. Or, by clicking on the “Open GRASS Tools” icon in the Quantum GIS GUI.
2. In the GRASS tools module, to conduct a buffer on the protected areas and ferry routes vector files we use the “v.buffer” command. [4] This module can be accessed in GRASS tools by either selecting it from the “modules tree” or “modules list” in the GRASS tools GUI or entered directly at the command line.
3. In the GRASS tools GUI, navigate to the “v.buffer” module using one of the methods described above. This module requires the fulfillment of three fields.
4. “Name of input vector map” – select the vector file which you wish to conduct a buffer on. - Note, vector file must be located in the mapset which you created when setting up your GRASS database
5. “Buffer distance along major axis in map units” – input the buffer distance taking into consideration the map units which your current project is using.
6. “Name of output vector map” – Define the name that you wish to call your output vector map.
7. Click Run, GRASS will take a few moments to process this request. Once the buffer has successfully finished you can click the “View Output” icon to add the resultant buffer to the layers available in your map.
The command line output used in this project can be seen below:
v.buffer input=FerryRoute@AtlCan type=line layer=1 distance=0.1 output=Bufferv1
v.buffer input=ProtectArea@AtlCan type=area layer=1 distance=0.2 output=ProtectBuffer
Where the input vector map in which the buffer is applied is “ProtectArea” and the mapset where this file is located is “AtlCan”. “type” refers to the format of the vector file which was areas of protected land. “layer” refers to the layer number, the default in GRASS is 1. “distance” is the buffer distance in map units being utilized in the map CRS. “output” is the name of the output vector map created by the buffer.
Visualization of Outputs
Now that the relative features and analyzed outputs have been created and integrated into one package the decision making process can begin. The role of decision makers involved in the site selection of an offshore oil platform can be facilitated through the visualization of the associated geographic features similar to those generated in this tutorial. By displaying and taking into account the number of different features which have an impact on the potential site location, decision makers can make more informed decisions in regards to allocating a specific site for an oil platform. The WMSs and open source software employed in this tutorial provide an exemplar framework for the processes involved in making efficient use of freely available data and software that can be utilized in practical business applications.
References
OGR. 2010. “OGR Simple Feature Library”. Date Accessed: November 27, 2010. Retrieved from: http://www.gdal.org/ogr/
QGIS. 2010. “User Guide. Version 1.5.0.” Date Accessed: November 22nd, 2010. Retrieved from: http://download.osgeo.org/qgis/doc/manual/qgis-1.5.0_user_guide_en.pdf
