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The starting data is the file 'topo_nlc.dat', that is a text file with xyz of a grid (5800 points)
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Create a new layer 'rectangle' and set it as 'layer to use' to separate the new rectangle of the topography
Geometry->Create->Object->Rectangle
33,-2865760,0
-8281,-2870880,0
Topography (transparent layer) and rectangle in XY and XZ views
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Then the model must have only the surfaces that enclose a volume ,create it with
Geometry->Create->Volume->By contour
and select all surfaces
Final volume and detail of cutted surfaces
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