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Give coastline SHP file a 0 value

NEV
NEV Global Mapper UserTrusted User
edited May 2014 in Technical Support
I have a New Zealand contour data set that begins at 20 metres with no zero value. A separate data set is a SHP file of the coastline but has no elevation value. I can display both sets - but when drawing an Elevation Grid the model stretches across harbours and embayments i.e. does not stop at the coast. Can I edit the coastline file to give it a value and combine the two sets so the Elevation Grid stops at the coastline.

Thanks

Comments

  • global_mapper
    global_mapper Administrator
    edited May 2014
    Yes, if you have the coastline just select the line(s) in that layer with the Digitizer Tool and edit them, then edit them and add an ELEVATION attribute with a value of 0. Then use the Analysis menu command to create an elevation grid and select the contour and coastline layers. That should enforce the coastline at 0. However you would still get it crossing things like harbors.

    To fix that once you have the grid I would suggest going to the Alter Elevations tab of the Options dialog for the layer and set the minimum valid elevation to something just above 0, like 0.01 meters. That should eliminate the filled in bays and such as they would all be at 0, but still give you the remaining terrain very close to the shoreline contour.

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation
  • NEV
    NEV Global Mapper User Trusted User
    edited May 2014
    Yes, if you have the coastline just select the line(s) in that layer with the Digitizer Tool and edit them, then edit them and add an ELEVATION attribute with a value of 0. Then use the Analysis menu command to create an elevation grid and select the contour and coastline layers. That should enforce the coastline at 0. However you would still get it crossing things like harbors.

    To fix that once you have the grid I would suggest going to the Alter Elevations tab of the Options dialog for the layer and set the minimum valid elevation to something just above 0, like 0.01 meters. That should eliminate the filled in bays and such as they would all be at 0, but still give you the remaining terrain very close to the shoreline contour.

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation

    Thanks Mike, it worked for most harbour-bay entrances but there is a small glitch where there are islands and the grid projects land elevations into the water- see image attached.

    Regards

    Neville
  • global_mapper
    global_mapper Administrator
    edited May 2014
    Are there shoreline lines around the islands that have an elevation of 0? You would need those to ensure that the area between the outer shoreline and the islands was exactly at 0.

    One other alternative if you have polygon boundaries for the shoreline is to simply crop the grid to those shoreline boundaries either on export to a new grid or just on the Cropping tab of the Options dialog for the layer.

    And finally you could check the box to save a TIN layer when creating the grid. Then delete any triangles that you don't want, then grid that TIN layer and close the original grid layer.

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation
  • NEV
    NEV Global Mapper User Trusted User
    edited May 2014
    Are there shoreline lines around the islands that have an elevation of 0? You would need those to ensure that the area between the outer shoreline and the islands was exactly at 0.

    One other alternative if you have polygon boundaries for the shoreline is to simply crop the grid to those shoreline boundaries either on export to a new grid or just on the Cropping tab of the Options dialog for the layer.

    And finally you could check the box to save a TIN layer when creating the grid. Then delete any triangles that you don't want, then grid that TIN layer and close the original grid layer.

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation

    Aha - the small islands are shown in the contour set - but not in the coastline data set. I now have a Coastline polygon that shows them so will use that and see how I go.

    Thanks as always for your prompt and "spot-on" assistance.

    Any progress on depression contours in a forthcoming GTM version?

    Kind Regards

    Neville
  • global_mapper
    global_mapper Administrator
    edited May 2014
    Neville,

    I'm glad everything is working now. There hasn't been any work done on generating depression contours as of yet. Not sure of a time-frame for that one.

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation
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