Problems with the Web Map Service Open GIS specification
Titel:
Problems with the Web Map Service Open GIS specification
Auteur:
Jan Růžička Michal Šeliga
Verschenen in:
Acta Montanistica Slovaka
Paginering:
Jaargang 10 (2005) nr. 2 pagina's 192-197
Jaar:
2005
Inhoud:
The paper is not focused on the area of GeoWeb generally, because there is a lot of papers written on this topic (for examples: see the proceedings from the symposium GIS Ostrava (http://gis.vsb.cz) the present). Author looks at the area from a different point of view. Is there anything wrong that comes with the Web Map Service (WMS) specification? WMS (antl of course other specifications from the Open GIS Consortium (http://www.opengis.org) brings new possibilities how to make GIS interoperable. The map server compatible with WMS specification publishes, upon a user request, the map as a raster (bitmap) file that can be visualized by the user’s client. The bitmap can be filled up with pixels with some color values but there can be transparent pixels too. That’s why outputs from more than one map server in one map client (like in the digital cartography) can be published. This possibility makes a big family of the data sources from the WMS servers that can be combined in many different ways. The user can obtain actual data from different sources and visualize them together. This advantage brings many disadvantages, which are described in the paper. There are problems with the symbology used. Data publishers can use so much different symbology (for example geologist, demographer), that the map server’s outputs should not be (quite often it is not possible eithn) putted together. A more serious is a problem in the quality and temporal extent of the data. The user can combine the data with a different temporal extent and upon a visual comparison he can produce a wrong decision. For example, the harlot must be closed because there is a school in a distance less than 50 meters but the school is closed for more than two years and is used for the accommodation of the foreign workers. Another example: a school administration localised the school building with a precision to the street (it means to the centre of the street), but the school building is at the beginning of the street, that means that the distance to the harlot is greater than 50 meters. The paper discuses other aspects of this problems and suggests some solution. Standard ISO/DIS 19128 brings some possibilities but all of them are optional only. WMS without metadata is a half of the solution for the GeoWeb. Standard ISO/DIS 19128 must define metadata as a mandatory item for the GetCapabilities operation. Other part of the problem is based on the metadata evaluation. The data quality evaluation and the comparison methodology must be specified and a new web service for the data quality comparison has to be developed. There is a lot of other problems with WMS but most serious of them is a problem with the SOAP protocol. Nowadays, web services developers think of a way of SOAP protocol only and ISO/DIS 19128 does not care of that way of development. ISO/DIS 19128 must define SOAP requests and responses for WMS, otherwise GIS will be still isolated from the surrounding world.
Uitgever:
Technical University of Kosice, the Faculty of Mining, Ecology, Process Control and Geotechnologies (F BERG)
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