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Thread:
Issue: Will adopting GML as the framework for TransXML result in a loss in engineering precision/ac |
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Paul Scarponcini
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Issue: Will adopting GML as the framework for TransXML result in a loss in engineering precision/ac
Posted:
Saturday, January 29, 2005 3:54 PM (EST)
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(I have separated out what are emerging as key issues regarding GML into separate threads to encourage focused discussion on these topics.)
One advantage cited for using GML is the existing, robust set of geometry types already available. These types derive from the ISO 19107 standard. Though the scope of this standard is quite general, that is, “spatial characteristics of geographic features”, its origin in GIS is not disputed. Applicability to TransXML during the planning, maintenance, and operation phases is therefore likely. This may not be the case during design. Assessing whether GML meets engineering needs, it is probably a more accurate assessment that it is incomplete rather than incorrect. It does include points with up to three decimal coordinates as would be needed to support survey points and (straight) linestrings of points to support breaklines. Spiral curves in a horizontal alignment and parabolic curves in a vertical profile are another issue. Though GML may support a mathematical definition of spiral or parabolic curves (or even circular ones for that matter), the representation scheme may appear foreign to engineers.
By recommending GML, the Project Team is not advocating that we should settle for only those geometry types available in GML as they currently exist there. We propose using what is there when it matches our requirements for precision, clarity, and efficiency. Where this is not possible, we propose to use alternative geometry types that meet the engineering requirements. To do this, we look to what LandXML uses. If we find deficiencies in LandXML, we will make specific proposals through LandXML.org to extend LandXML. We may also encourage GML (and LandGML) to adopt these extensions, but this will not be done as part of this project.
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