C.1 Limitations of this tool
ArcMap is able to perform analytical tasks on large volumes of data, but when compared to the latest developments in the mobile GI field using it to create a mobile directory seems like overkill.
Mobility is restricted as it operates on static datasets whilst requiring a client with significant processing capacity and an external server offering interaction and presentation GI services.
Using reverse-geocoding the tool is able to perform spatial queries depending on post-code information, however with each post-code indentifying between 1 and 100 unique addresses, the accuracy level of the spatial query performed is depended on the type of location clicked on the map (street numbers on larger roads usually have longer distance between them). In addition, the search tolerance setting on the ArcMap document, used within the VB script1 will influence heavily the post-code returned.
C.2 Is Google Local thorough in identifying available services? How about searching information other than 'services'; What type of limitations exist in querying spatial information in generally?
Google Local is a location-based service, accessible via thin client architecture. It allows querying by specifying various spatial search criteria and is supported by services2 responsible to convert the textual descriptions to spatial coordinates. However, with queries containing evaluative criteria such as ‘which is the best restaurants in Leytonstone’, the results span all over across London; the user needs to pan the map or filter based on distance to focus in the area preferred. When the term ‘best’, was replaced with ‘cheapest’, irrelevant results regarding property maintenance services were returned. More ambiguous qualitative queries like ‘the most expensive street in London’ did not return relevant results. It is understood that such a complex process of extracting semantically correct meaning out of verbose queries spans in many different scientific research fields, including linguistics, AI etc, therefore such inconsistencies in the results must be within the user’s expectations. But is apparent that the work that has been invested in such a tool has yield in a extremely efficient service with lots of options, which it can only be further improved.
C.3 Would a search of all Internet resources provide further information; What alternatives are there to using a postcode for spatial queries;
Extending the search using a search engine yields many results with potentially exact and relevant information; however there are fundamental differences in the algorithms behind search engines with those behind GI directory services which suffer from the lack of universally agreed geography type; An attempt to tackle this problem is provided by the GeoXwalk3 project: geometric computations introduce a mechanism to resolve spatially complex queries4 describing relationships between features with complex geographic boundaries. Further development has been done to enable advanced querying5 by “explicitly georeference implicitly georeferenced material” (geoXwalk Phase III - Final Report, 2004) .
C.4 Availability in other regions and countries
According to Google(6), there is an ongoing process on making this service available everywhere in the world, but this is not the case yet; though a workaround exists by creating a public My Map to list any business information which then can be searched using Google Maps7.
C.5 References
1. ‘ get the postcode
Dim postcode As String
postcode = getPostcode(pMxDoc.SearchTolerance, pPoint, pMxDoc.FocusMap)
2. Such as gateway location services, directory services, geocode services, route determination services etc.
3. Reid, James & Medyckyj-Scott, David., 2004. GeoXwalk Phase III – Final Report. Available at: http://edina.ac.uk/projects/geoxwalk/documents/geoXwalk%20Phase%20III%20Final%20report.doc[Accessed April 12, 2010].
4. i.e. ‘which rivers are near Banbury? ’ (geoXwalk Phase III – Final Report, 2004)
5. i.e. ‘find me all documents about Gaelic songs that do not reference the Western Isles or, find me images of towns along the river Tweed’ (geoXwalk Phase III – Final Report, 2004)
6. Maps features available in your country – Maps Help. Available at: http://maps.google.com/support/bin/answer.py?hl=en&answer=16634 [Accessed April 12, 2010].
7. http://www.google.com/support/forum/p/maps/thread?tid=7f1a2dcf8c70f97c&hl=en
Showing posts with label GITA. Show all posts
Showing posts with label GITA. Show all posts
Thursday, 6 May 2010
Practical B - Internet GIS
B.1 Functionality, strengths and weaknesses
A core element of Web 2.0, mashups enable information sharing and interoperability by combining data from different external sources. With the adoption of web standards like RSS, online tools now allow the user to create and publish mash-ups with relative ease. Such tools are the Mapbuilder (tool for overlaying pin-points and tags over a map) and the Yahoo Pipes, with more sophisticated integration of various data sources. Both use cartographic and geographic data to produce a map; the user can then choose to add information related to location.
B.2 Yahoo pipes usability and mashup implementation(4)
Yahoo Pipes is a Javascript application with a visual interface that includes various tools referred to as modules. Each module can accept a data source as input, manipulate it, and pipe its output to a different module. The process follows the imperative programming paradigm: inputs and outputs can be processed using modules like the Loop operator (iterating over the result-feed of its input), String functions, URLBuilder etc. The final feed can be georeferenced by using the Location Extractor module; given a string that contains a place name it attaches GeoRSS standard spatial coordinates to it. Inherent ambiguity limits its accuracy; different places with the same name do exist. The output stream of data can be exported as JSON or RSS feed. Of particular interest, is the YQL module: using sql-like syntax the user can query and filter the content of an RSS feed. This feature is used on the example pipe. Finally, the RSS-Item Builder restructures the modified data sources as an RSS feed, which then can be piped to the output.
B.3 Usability, flexibility and extensibility
B.4 References
1. Map Builder url: http://www.mapbuilder.net/users/panoramix95/83622
2. Yahoo Pipes url: http://pipes.yahoo.com/gita_abhp626/reuter_news_and_flicker_photos
3. Pipes Blog » Blog Archive » Connection refused and other Pipes issues. Available at: http://blog.pipes.yahoo.net/2009/12/10/connection-refused-and-other-pipes-issues/
[Accessed April 7, 2010]
4. Pipe implementation screen shot
A core element of Web 2.0, mashups enable information sharing and interoperability by combining data from different external sources. With the adoption of web standards like RSS, online tools now allow the user to create and publish mash-ups with relative ease. Such tools are the Mapbuilder (tool for overlaying pin-points and tags over a map) and the Yahoo Pipes, with more sophisticated integration of various data sources. Both use cartographic and geographic data to produce a map; the user can then choose to add information related to location.
The produced examples have as intended audience the consumer. The Mapbuilder shows the locations of local sites in the island of Ikaria, Greece. The audience of Yahoo Pipes mashup could be someone interest in the world news with an option of accessing location related photos; this is achieved by overlaying the Reuters News RSS feed on a map using each story's location information, plus combining it with the Flicker Geo RSS service to produce a link on a relevant to location photo. There is a strong chance that the latest geo-tagged photo with a location same as the story will have relevant content though there is no guarantee of this.
Yahoo Pipes is a Javascript application with a visual interface that includes various tools referred to as modules. Each module can accept a data source as input, manipulate it, and pipe its output to a different module. The process follows the imperative programming paradigm: inputs and outputs can be processed using modules like the Loop operator (iterating over the result-feed of its input), String functions, URLBuilder etc. The final feed can be georeferenced by using the Location Extractor module; given a string that contains a place name it attaches GeoRSS standard spatial coordinates to it. Inherent ambiguity limits its accuracy; different places with the same name do exist. The output stream of data can be exported as JSON or RSS feed. Of particular interest, is the YQL module: using sql-like syntax the user can query and filter the content of an RSS feed. This feature is used on the example pipe. Finally, the RSS-Item Builder restructures the modified data sources as an RSS feed, which then can be piped to the output.
B.3 Usability, flexibility and extensibility
Both engines are easy to use for simple mashups, though Yahoo Pipes extended capabilities can challenge users with little or no programming experience. Additionally, Yahoo Pipes user interface is computationally demanding; integrating data from different web-services in the client machine proved a difficult task without reliable and fast internet connection, with errors related to connection refusal. According to Yahoo, there is an ongoing redesigning of the data flow engine based on the YQL functionality(3). Finally, Yahoo Pipes Badge allows the map output to be embedded in any web page by providing a widget with a guid; an excellent example of how GI mashups can add value to a website free of cost.
B.4 References
1. Map Builder url: http://www.mapbuilder.net/users/panoramix95/83622
2. Yahoo Pipes url: http://pipes.yahoo.com/gita_abhp626/reuter_news_and_flicker_photos
3. Pipes Blog » Blog Archive » Connection refused and other Pipes issues. Available at: http://blog.pipes.yahoo.net/2009/12/10/connection-refused-and-other-pipes-issues/
[Accessed April 7, 2010]
4. Pipe implementation screen shot
Practical A - Geodesy and positioning
A.1 The shape and the route
Regent’s Park’s inner circle made a good start point to explore routes appropriate for track-logging with some kind of pattern. The route was planned using Google maps service; its vector based maps are simple without excessive visual variables creating clutter; thus facilitating pattern recognition. The produced trail when projected on the map can be seen as a stickman with arms extending left and right in a throwing motion and legs positioned in a manner that indicates throw-assisting movement. With a relative quantum leap of imagination there is a scarf tied around the neck as well. In hindsight, producing this pattern was an ambitious aim; the track was traced on foot, and took a considerable amount of time. Non-anticipated closed paths encountered around the ‘bucket’ area and are responsible for the ‘scarf’ detail. In a perfect world, the long neck would have been much shorter and the circle-head could contain additional detail within.
A.2 Accuracy, error and appropriateness of the map
The GPS track was collected uninterrupted during one afternoon; during data collection the sky was clear with good visibility, and the GPS was triangulating consistently using 4 satellites. The only time that the signal was lost, was due to street narrowness and existence of big trees obscuring the sky (Park Crescent Mews str. with Marylebone Rd). In this case the GPS lost visibility of all satellites, but the track path was not affected as the distance covered under such conditions was very short.
Is fairly obvious that the overall match of the GPS data and the backdrop map is quite good, making apparent that there was a sufficiently strong signal, tracking the route with high accuracy. There aren’t any particular mismatches, and where a multipath is plotted is due to the paths followed to draw the stickman’s hands and legs which were backtracked – thus track-logged twice. Occasionally, people and traffic lights necessitated diversion from a straight route.
The GPS track was collected according to the WGS841 geodetic system; to project on a 2D coordinate system, the track was transferred to ArcView via the GPSi interface and transformed using the OS British Grid2 by selecting the OSGB_1936_To_WGS_1984_Petroleum3 transformation, which allows for a deviation(4) up to 4 metres; thus there is certainly some degree of error since no exact transformation between two geodetic coordinate systems exist(5). During the transformation process a message ‘The output resolution is larger than the input feature class resolution’ was produced, due to the fact that the output geoprocessing tools in ArcGIS 9.2 is 53-bit7.
Finally, to overlay the track, two backdrop maps, one raster and one vector based were used. The scale of the raster map is 1:25,000, allowing the streets to be distinctly visible; both maps were downloaded from Edina. The track log, and the two maps where overlaid using ArcMap. Note that it was not necessary to create a new Geodatabase, and all layers where created by simple opening the Mastermap gz file.
A.3 References
1. A 3D geodetic coordinate system, that comprises a standard coordinate frame for the earth, with a spheroid surface. (http://en.wikipedia.org/wiki/World_Geodetic_System)
2. A system of geographic grid references commonly used in Great Britain.
http://en.wikipedia.org/wiki/British_national_grid_reference_system
3. This transformation uses the parameters recommended by Ordnance Survey for a Helmer(6) transformation; http://geometrybag.wordpress.com/2006/05/03/osgb-transformations-inside-arcgis/
4. A statistic value that represents the amount of disagreement among points with known longitude and latitude in a coordinate system, when compared with a different coordinate system. http://www.ordnancesurvey.co.uk/oswebsite/gps/information/coordinatesystemsinfo/guidecontents/guide6.html
5. Welcome to GPS Network. Ordnance Survey – Great Britain's national mapping agency. www.ordnancesurvey.co.uk/oswebsite/gps/information/coordinatesystemsinfo/guidecontents/guide6.html
[Accessed March 31, 2010].
6. Helmert transformation: The rotation and translation of a network of points relative to the Cartesian axes, while leaving the shape of the figure unchanged;
7. Technical Articles - ESRI Support. Available at: http://support.esri.com/index.
Regent’s Park’s inner circle made a good start point to explore routes appropriate for track-logging with some kind of pattern. The route was planned using Google maps service; its vector based maps are simple without excessive visual variables creating clutter; thus facilitating pattern recognition. The produced trail when projected on the map can be seen as a stickman with arms extending left and right in a throwing motion and legs positioned in a manner that indicates throw-assisting movement. With a relative quantum leap of imagination there is a scarf tied around the neck as well. In hindsight, producing this pattern was an ambitious aim; the track was traced on foot, and took a considerable amount of time. Non-anticipated closed paths encountered around the ‘bucket’ area and are responsible for the ‘scarf’ detail. In a perfect world, the long neck would have been much shorter and the circle-head could contain additional detail within.
A.2 Accuracy, error and appropriateness of the map
The GPS track was collected uninterrupted during one afternoon; during data collection the sky was clear with good visibility, and the GPS was triangulating consistently using 4 satellites. The only time that the signal was lost, was due to street narrowness and existence of big trees obscuring the sky (Park Crescent Mews str. with Marylebone Rd). In this case the GPS lost visibility of all satellites, but the track path was not affected as the distance covered under such conditions was very short.
Is fairly obvious that the overall match of the GPS data and the backdrop map is quite good, making apparent that there was a sufficiently strong signal, tracking the route with high accuracy. There aren’t any particular mismatches, and where a multipath is plotted is due to the paths followed to draw the stickman’s hands and legs which were backtracked – thus track-logged twice. Occasionally, people and traffic lights necessitated diversion from a straight route.
The GPS track was collected according to the WGS841 geodetic system; to project on a 2D coordinate system, the track was transferred to ArcView via the GPSi interface and transformed using the OS British Grid2 by selecting the OSGB_1936_To_WGS_1984_Petroleum3 transformation, which allows for a deviation(4) up to 4 metres; thus there is certainly some degree of error since no exact transformation between two geodetic coordinate systems exist(5). During the transformation process a message ‘The output resolution is larger than the input feature class resolution’ was produced, due to the fact that the output geoprocessing tools in ArcGIS 9.2 is 53-bit7.
Finally, to overlay the track, two backdrop maps, one raster and one vector based were used. The scale of the raster map is 1:25,000, allowing the streets to be distinctly visible; both maps were downloaded from Edina. The track log, and the two maps where overlaid using ArcMap. Note that it was not necessary to create a new Geodatabase, and all layers where created by simple opening the Mastermap gz file.
A.3 References
1. A 3D geodetic coordinate system, that comprises a standard coordinate frame for the earth, with a spheroid surface. (http://en.wikipedia.org/wiki/World_Geodetic_System)
2. A system of geographic grid references commonly used in Great Britain.
http://en.wikipedia.org/wiki/British_national_grid_reference_system
3. This transformation uses the parameters recommended by Ordnance Survey for a Helmer(6) transformation; http://geometrybag.wordpress.com/2006/05/03/osgb-transformations-inside-arcgis/
4. A statistic value that represents the amount of disagreement among points with known longitude and latitude in a coordinate system, when compared with a different coordinate system. http://www.ordnancesurvey.co.uk/oswebsite/gps/information/coordinatesystemsinfo/guidecontents/guide6.html
5. Welcome to GPS Network. Ordnance Survey – Great Britain's national mapping agency. www.ordnancesurvey.co.uk/oswebsite/gps/information/coordinatesystemsinfo/guidecontents/guide6.html
[Accessed March 31, 2010].
6. Helmert transformation: The rotation and translation of a network of points relative to the Cartesian axes, while leaving the shape of the figure unchanged;
7. Technical Articles - ESRI Support. Available at: http://support.esri.com/index.
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