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OS VectorMap Local

Removal of Spot Heights and Air Heights from VML

    • 4 December 2017 08:39AM
    • Visits: 3
    • Discussions: 1
    • Responses: 0
    • Registered: 18 September 2015 07:47AM
    • Last active: 4 December 2017 08:31AM

    As you will be aware from recent communications, we are in the process of changing how we create VectorMap Local (VML).

    Using an entirely automated approach we aim to improve consistency, currency and accuracy across the product.

    As part of this iterative process we are assessing the quality of many aspects of the data within the product and would like to highlight a planned change concerning the current depiction of Spot Heights and Air Heights. Spot Heights are measured heights above datum at a given point, from ground survey, whilst Air Heights are created from stereo interpretation of aerial photography.

    Existing VML has both spot heights and air heights within the raster and vector product (GML feature codes 15405 and 15406). Examples of these are shown attached in Figures 1 and 2. These heights were originally captured using manual levelling techniques and not actively maintained in the digital era with new surveying methods being employed to capture and maintain height information.

    As we look to improve the quality and consistency of data used to create the new VML product, we are proposing that the source for these heights should be the same maintained height content stores those that are used to generate our existing Terrain 5 and Terrain 50 products. This will result in accurate and maintained contour data in the vector dataset, and from that same source we will extract spot heights that are in sympathy with surrounding contours.

    By changing the source of the spot height information to a maintained, consistent accurate one, the proposed impact on the new VML product will be;
    • Spot Heights and Air Heights will be merged in to a single feature
    • Spot heights will continue to be shown but reduced significantly in number (for example, spot heights along roads as shown in the examples attached will be removed).
    • Spot height will only be shown in areas where the contour is closed (such as a hill top) and the difference in altitude is at least 1 metre above or below the surrounding contour (fig 3).

    We would like to hear from you if this change will have any impact upon your use of the VML raster or vector product during December 2017. This will help our development teams to implement any changes based upon your feedback

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