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Section interpolation

Once the topographic profile is loaded and at least 2 boreholes are in, GeoSection builds the continuous geological section by interpolating stratigraphic contacts between the boreholes projected onto the trace.

Borehole projection on the trace

Each borehole has coordinates (x, y) in the plane. The section trace is a polyline on the same plane. The projection is the orthogonal distance of the borehole onto the nearest segment of the polyline:

  • progressive distance along the trace: x-coordinate of the perpendicular foot;
  • lateral distance: how far the borehole is from the trace (shown in legend — a borehole >50 m off trace should be assessed cautiously).

Boreholes appear in the section as vertical columns at their projected abscissa, with the head at the indicated elevation and layers coloured by depth.

Stratigraphic contact interpolation

The classical algorithm is piecewise linear interpolation between matching contacts (same layer code) of adjacent boreholes:

  1. For each borehole the absolute elevations of contacts are computed (head_elevation - depth).
  2. Between two adjacent boreholes that both have a contact for layer X, a straight segment is drawn joining them.
  3. If one is missing, the contact extends horizontally to the domain edge or to the next borehole where it reappears.

The result is a series of stratigraphic polygons filling the section between the topography and contacts.

AI: automatic section description

Pressing AI → Describe section sends a text summary of the geometry to the multimodal model: - number of layers and their codes; - stratigraphic succession (top to bottom); - presence of lenses, heteropies, recognisable discontinuities; - water-table depth and extent.

Returns a descriptive paragraph to paste into the technical report. Uses Gemini 1.5 Pro server-side.

When the AI gets it wrong

The AI interpretation is descriptive, not geomechanical: it describes what it sees on the section, it doesn't replace the geologist's judgement. On sections with very thin layers (<50 cm) or distant boreholes (>200 m) the description tends to over-generalise.

Water table

If the boreholes carry the water-table level (wstk_depth field in AGS4 or analogous column in CSV), GeoSection draws a blue zigzag line joining the water levels of adjacent boreholes. It does not interpolate between permeable and impermeable layers — it's a pure geometric projection.

To manually edit the water table: panel Discontinuities → Water table → edit points.

Lenses and manual contacts

For cases the linear algorithm doesn't handle well (closed lenses, layer missing in the middle due to erosional discordance) you use manual contacts:

  1. Panel Stratigraphy → Contacts.
  2. Add a contact by entering progressive abscissa (m) + elevation (m a.s.l.) + upper/lower layer.
  3. The section regenerates automatically including the manual contact.

This lets you represent lenses, unconformities, faults, intrusions — even when the boreholes don't intercept them directly.