Why are drillhole cross-sections displayed in non-earth co-ordinates in the map window?

Occurrence

Drillhole cross-sections created using the Drillholes>Define New Section or Plan menu option display
the X axis co-ordinates in non-earth units, rather than real world units (e.g. UTM).


Solution

Discover will only display cross-sections in real world co-ordinates if the section orientation/azimuth is
precisely parallel to one of the principal axes (i.e. E-W / 90 degrees or S-N / 0 degrees). If the section
orientation is either at an angle (e.g. 35 degrees) or even very slightly oblique (less than a degree) to
the either of the principal axes, the section mapper window will be displayed in non-earth units.

This is because Mapinfo requires a precise 1:1 ratio between the X and Y (depth in the case of
cross-sections) units in a mapper window. Sections not precisely parallel to the principal axes will
therefore have both an easterly and northerly component along the X axis. Neither of these components
will have a 1:1 relationship with the depth (Y) axis.

For these 'angled' sections, Discover utilises a non-earth system along the X axis, ensuring a 1:1 ratio with
the Y axis.

However once the section is added to a layout window (Drillholes>Add Section to Layout), or a section grid added (Drillholes>Draw Section Grid)
a map grid incorporating both the real world eastings and northings will be generated.

NOTE: The Discover>Map Grid or Autogrid will still display the inline distance, not easting/northings.

To ensure that a section line is drawn parallel to a principal axis, hold down the SHIFT key whilst drawing 
the section line. This will ensure that the section mapper window utilises real world co-ordinates along
the X axis.

Also note that this will only work if the view direction is the default 0 (for E-W sections) or 90  (for S-N)
degrees, because MapInfo requires real world projections co-ordinates to have the X-axis (eastings)
increasing left to right.

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11th September 2007 12:56:02 pm

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