Isolating resistive, conductive, and background bodies

A single resistivity volume mixes conductors, resistors, and the background medium into one cloud. The most useful interpretive trick is to peel them apart: render only the cells in a chosen resistivity window, so a conductor or a resistive block stands alone in space. rho_range does exactly this — it sets the volume’s isomin/isomax, hiding everything outside the band.

Here the WILLY_DATA volume (ρ ≈ 4 – 10⁵ Ω·m) is split into conductive (< 100 Ω·m), background (100 – 1000 Ω·m), and resistive (> 1000 Ω·m) bodies, all draped on topography. Every scene is interactive.

Load the survey

import os

from pycsamt.map import MapView


DATA = os.path.join(
    os.environ.get("PYCSAMT_DOCS_REPO_ROOT", "."), "data", "AMT", "WILLY_DATA"
)
mv = MapView.from_folder(DATA, recursive=True)
print(f"{mv.n_stations} stations across {len(mv.lines)} lines")

53 stations across 2 lines

The 2-D slices through the volume

Before isolating bodies, the depth mode shows the volume as a stack of horizontal 2-D maps — a reference for where the conductors and resistors sit at each level.

fig = mv.map3d(mode="depth", n_slices=6)
fig.update_layout(height=640, scene_aspectmode="cube")
fig

The full resistivity block

The complete volume, draped on topography — every resistivity class present at once. The examples below carve this apart.

fig = mv.map3d(mode="block", opacity=0.5, show_stations=True, station_size=3)
fig.update_layout(height=640, scene_aspectmode="cube")
fig

Conductive block only

rho_range=(1, 100) keeps only cells below 100 Ω·m — the conductors (clay, alteration, fluids) isolated from everything else, so their shape and depth are unobstructed.

fig = mv.map3d(
    mode="block",
    rho_range=(1.0, 100.0),
    opacity=0.75,
    show_stations=True,
    station_size=3,
)
fig.update_layout(height=640, scene_aspectmode="cube")
fig

Resistive block only

The complementary view: rho_range=(1000, 100000) shows only the resistive bodies (fresh basement, intrusions), which here form the bulk of the deeper survey.

fig = mv.map3d(
    mode="block",
    rho_range=(1000.0, 100_000.0),
    opacity=0.55,
    show_stations=True,
    station_size=3,
)
fig.update_layout(height=640, scene_aspectmode="cube")
fig

Background medium only

Isolating the intermediate band rho_range=(100, 1000) leaves the “host” medium — everything that is neither a marked conductor nor a strong resistor. Comparing the three isolations shows how the survey volume partitions.

fig = mv.map3d(
    mode="block",
    rho_range=(100.0, 1000.0),
    opacity=0.5,
    show_stations=True,
    station_size=3,
)
fig.update_layout(height=640, scene_aspectmode="cube")
fig

Iso-surface of a single class

For a crisp boundary rather than a semi-transparent cloud, mode="surface" with the same rho_range draws the iso-surface enclosing the conductive body — the cleanest way to communicate a target’s geometry.

fig = mv.map3d(
    mode="surface",
    rho_range=(1.0, 100.0),
    surface_count=6,
    opacity=0.6,
    show_stations=True,
    station_size=3,
)
fig.update_layout(height=640, scene_aspectmode="cube")
fig

Takeaway. rho_range turns one volume into a set of resistivity-class views — conductor, background, resistor — each draped on topography and referenced to the stations. Combine with Near-surface 3-D view with topography and stations to isolate a class within the near-surface window.