Import roughness map from shapefile without elevation

[dryad]

When I import a shapefile roughness map (ESRI Shapefile maps) consisting only of roughness lines, mapeditor sets the Z values of the lines to 0.

Setting the attribute header for Elevation to (disabled) has no effect, and the line is still assigned an elevation of 0.
ESRI shapefiles can't have values of null or 'blank' in numeric fields, so I can't see any way of changing how this works.
Alternatively I couldn't find a way to assign all elevations to null after importing.
Any suggestions? Have I missed something? Thanks.

[Niels Gylling Mortensen]

Dear dryad,
My colleague Ole Rathmann has this answer to your question:

"First, in principle we cannot know whether, in a shape file, a roughness change line with Z=0 actually MEANS an elevation of zero or just “nothing” – so the problem cannot be dealt with automatically.


However, in MapEditor 11 you may multiple-select a bunch of roughness change lines (different roughness values) but all with z=0, and then use the “Edit line properties” option to deselect the elevation for all of them …, but leaving the individual roughness values unchanged."


Hope this helps.


Best regards,
Niels

[dryad]

Thank you both for the response.
With some investigation, I found that 'Edit line properties' gives an error 'The selected polylines are of unequal category' if one open line and one closed line are selected. This was what was stopping me using the method suggested to reassign. Is this by design?


On your first point, when importing a shape file, the 'Polyline-attribute header specification' window allows the Elevation setting to be (disabled), so I would suggest that might allow you to automatically identify elevations to ignore. Typically I create elevation and roughness shape files separately.


Thanks again for the help,
Daniel