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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
...
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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