gemgis

name	gemgis
description	Spatial data processing for geological modelling with GemPy. Use when Claude needs to: (1) Prepare spatial data for GemPy models, (2) Extract interface points from geological maps, (3) Process orientations/dip measurements, (4) Sample DEMs along profiles or cross-sections, (5) Convert between GIS formats and GemPy inputs, (6) Clip/transform vector/raster data for modeling, (7) Create model extents from geospatial bounds.
version	1.0.0
author	Geoscience Skills
license	MIT
tags	["GIS","Geospatial","Data Preparation","DEM","Geological Modelling"]
dependencies	["gemgis>=1.0.0","geopandas","rasterio"]
complements	["gempy","loopstructural","pyvista"]
workflow_role	processing

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

Module	Purpose
gemgis.vector	Vector data processing, XYZ extraction
gemgis.raster	Raster/DEM processing, sampling, interpolation
gemgis.utils	Utility functions, extent management
gemgis.postprocessing	Model postprocessing

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

Format	Extension	Read	Write
Shapefile	.shp	Yes	Yes
GeoJSON	.geojson	Yes	Yes
GeoPackage	.gpkg	Yes	Yes
GeoTIFF	.tif	Yes	Yes
ASCII Grid	.asc	Yes	Yes

Common CRS

EPSG	Description
4326	WGS84 (lat/lon)
32632	UTM Zone 32N
32633	UTM Zone 33N

When to Use vs Alternatives

Scenario	Recommendation
Prepare GIS data for GemPy modelling	GemGIS - purpose-built bridge between GIS and GemPy
General geospatial analysis in Python	geopandas + rasterio - more flexible, larger community
GUI-based geological map processing	QGIS - visual, interactive, plugin ecosystem
Extract XYZ + elevation from shapefiles and DEMs	GemGIS - one-liner with extract_xyz()
Complex raster analysis pipelines	rasterio + xarray - more control and scalability

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