Steadfastasart Geoscience Skills Gemgis

GemGIS - Geospatial Data for Geological Modelling

Quick Reference

import gemgis as gg
import geopandas as gpd

# Load vector data
gdf = gpd.read_file('geology.shp')

# Extract XYZ from geometry with elevation from DEM
interfaces = gg.vector.extract_xyz(gdf=gdf, dem='dem.tif')

# Define model extent
extent = [x_min, x_max, y_min, y_max]

# Clip to extent
gdf_clipped = gg.vector.clip_by_extent(gdf=gdf, extent=extent)

Key Modules

Essential Operations

Extract Interface Points

contacts = gpd.read_file('contacts.shp')
interfaces = gg.vector.extract_xyz(gdf=contacts, dem='dem.tif')
interfaces['formation'] = contacts['formation']
# Returns DataFrame with X, Y, Z, formation columns

Extract Orientations

measurements = gpd.read_file('structural_measurements.shp')
orientations = gg.vector.extract_xyz(gdf=measurements, dem='dem.tif')
orientations['dip'] = measurements['dip']
orientations['azimuth'] = measurements['strike'] + 90  # strike to dip direction
orientations['formation'] = measurements['formation']

Sample DEM Along Profile

profile = gg.raster.sample_from_raster(
    raster='dem.tif',
    line=[(500000, 5600000), (510000, 5605000)],
    n_samples=100
)
# Returns dict with 'distance' and 'Z' arrays

Define Model Extent

# From coordinates
extent = gg.utils.set_extent(
    x_min=500000, x_max=510000,
    y_min=5600000, y_max=5610000
)

# From GeoDataFrame bounds
extent = gg.utils.set_extent_from_bounds(gdf)

Clip Data to Extent

from shapely.geometry import box
extent_poly = box(500000, 5600000, 510000, 5610000)
gdf_clipped = gdf.clip(extent_poly)

# Or using gemgis
gdf_clipped = gg.vector.clip_by_extent(
    gdf=gdf,
    extent=[500000, 510000, 5600000, 5610000]
)

CRS Conversion

# Always work in projected CRS (meters) for modeling
gdf_utm = gdf.to_crs('EPSG:32632')  # UTM zone 32N

# Or use GemGIS utility
gdf_utm = gg.vector.reproject(gdf, 'EPSG:32632')

Supported Formats

Common CRS

When to Use vs Alternatives

Choose GemGIS when: You are building a GemPy model and need to convert GIS data (shapefiles, DEMs, geological maps) into GemPy-compatible inputs. It eliminates boilerplate for common spatial data preparation tasks.

Avoid GemGIS when: You need general-purpose GIS analysis (use geopandas directly), or your workflow does not involve GemPy (the tool is specifically designed for that pipeline).

Common Workflows

Prepare geospatial data for GemPy model

• Load geological map (contacts, formations) with gpd.read_file()
• Reproject all data to a projected CRS (UTM) with gdf.to_crs()
• Define model extent with gg.utils.set_extent() or from GeoDataFrame bounds
• Clip vector data to extent with gg.vector.clip_by_extent()
• Extract interface XYZ from contacts using gg.vector.extract_xyz(gdf, dem)
• Extract orientation XYZ from structural measurements
• Convert strike to dip direction (azimuth = strike + 90)
• Validate that all data shares the same CRS and falls within extent
• Pass prepared DataFrames to GemPy model

Tips

1. Always check CRS - All data must be in the same coordinate system
2. Use UTM for modelling - Meters are easier than degrees
3. Assign Z from DEM - Ensures consistent elevations across datasets
4. Validate geometry - Fix invalid geometries before processing
5. Buffer extent slightly - Avoid edge effects in interpolation

References

• Data Extraction Methods - Extract interfaces, orientations, and profiles
• Vector and Raster Operations - Detailed processing workflows

Scripts

• scripts/prepare_gempy_data.py - Prepare spatial data for GemPy model input

Converted and distributed by TomeVault — claim your Tome and manage your conversions.