For example, a topographic grid has been created of an open cut pit (e.g. by overlaying a DEM grid with a series of donutted polygons representing pit bench levels using the Surfaces>Grid Utilities>Overlay tool).
You would like to examine those portions of the original exploration drillholes (drilled from surface) that lie either within or below this pit surface (the drillhole downhole data tables have been converted into a series
of individual points by desurveying them (Drillholes>3D coordinates), and Creating Points from these new XYZ co-ords).
Solution
1/. In MapInfo, create a new float -type field in the point TAB file (e.g. 'grid_value') using Table>Maintenance>Table.Modify Structure.
2/. With both datasets open in the same map window, select all the points and run the Surfaces>Utilities>Assign Values tool. Populate the new field (e.g. 'grid_value') with the output. Save the point table.
3/. Run a query (Query>Select) to compare the original Z value field with this new field.
4/. Save this query as a table
