nDSM Generator (Bavaria DGM1)

Generate normalized Digital Surface Models (nDSM) by automatically downloading Bavaria's DGM1 (Digital Terrain Model) via INSPIRE WCS 2.0.1 and computing the difference between your DSM and the DTM.

nDSM = DSM − DTM gives you the height of objects (buildings, vegetation, etc.) above ground level.

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Features

• Automatic DTM download from Bavaria's INSPIRE WCS service (DGM1, 1m resolution)
• CRS-aware processing — works with DSMs in any coordinate system
• Precise grid alignment — DTM is resampled to match your DSM's exact pixel grid
• Batch processing — process multiple DSM files in one go
• Secure credential handling via environment variables
• Flexible resampling — choose between nearest, bilinear, or cubic resampling
• Optimized output — compressed GeoTIFF files with proper nodata handling

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Repository Structure

18_nDSM_generator/
├── ndsm_generator.ipynb          # Single DSM processing
├── ndsm_generator_batch.ipynb    # Batch processing for multiple DSMs
├── modules/
│   └── ndsm_tools.py             # Core processing functions
├── requirements.txt              # Python dependencies
├── .gitignore
└── README.md

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Installation

Prerequisites

• Python 3.8+
• Valid credentials for Bavaria's geodata service (LDBV)

Setup

1. Clone the repository:

2. Set up credentials in your conda environment (recommended):

   conda activate your_env
   conda env config vars set LDBV_USER="your_username" LDBV_PASS="your_password"
   conda deactivate && conda activate your_env

   Alternatively, the notebooks will prompt for credentials if environment variables are not set.

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``bash conda activate your_env conda env config vars set LDBV_USER="your_username" LDBV_PASS="your_password" conda deactivate && conda activate your_env

**Option 2: Manual Entry**

The notebooks will prompt for credentials if environment variables are not set.

### Usage

#### Single DSM Processing

1. Open `ndsm_generator.ipynb`
2. Set your input DSM path and output paths
3. Run all cells

#### Batch Processing

1. Open `ndsm_generator_batch.ipynb`
2. Configure:
    `DSM_FOLDER` — folder containing DSM files
   - `OUTPUT_FOLDER` — where to save nDSM (CHM) files
   - `DTM_OUTPUT_FOLDER` — where to save DTM files
   - `DSM_PATTERN` — file pattern (e.g., `"*_DSM.tif"`)
3. Run all cells

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## Output Products

For each DSM, the pipeline generates:

1. **`*_DTM.tif`** — Raw DTM downloaded from WCS
2. **`*_DTM_aligned_to_DSM.tif`** — DTM resampled to exact DSM grid
3. **`*_CHM.tif`** or **`*_nDSM.tif`** — Height above ground (DSM − aligned DTM)

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## How It Works

```mermaid
graph LR
    A[DSM GeoTIFF] --> B[Extract AOI]
    B --> C[Transform to EPSG:25832]
    C --> D[WCS GetCoverage Request]
    D --> E[Download DTM]
    E --> F[Align to DSM Grid]
    F --> G[Compute nDSM]
    G --> H[Save Products]

1. Extract AOI: Read DSM extent and transform to EPSG:25832 (required by WCS)
2. Apply Buffer: Add small buffer (0-2m) to avoid edge artifacts
3. WCS Request: Download DGM1 coverage for the AOI
4. Grid Alignment: Resample DTM to match DSM's CRS, transform, and dimensions exactly
5. Compute nDSM: Subtract aligned DTM from DSM with proper nodata handling
6. Save Results: Write compressed GeoTIFF files

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Configuration Options

Parameter	Description	Default
BUFFER_M	Edge buffer in meters	2.0
PIXEL_M	Requested WCS pixel spacing	1.0
RESAMPLING	Resampling method	"bilinear"
GENERATE_NDSM	Create nDSM files (batch mode)	True

Resampling Methods

• bilinear — Recommended for most cases; smooth results
• cubic — Highest quality; slightly slower
• nearest — Preserves original values; best for categorical data

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Data Source & License

DTM Source: DGM1 — Bayerische Vermessungsverwaltung (LDBV)
License: CC BY 4.0
Service: INSPIRE WCS 2.0.1

Attribution Required: Please cite the data source in any publications or products:

"Digitales Geländemodell - Bayerische Vermessungsverwaltung (www.geodaten.bayern.de), CC BY 4.0"

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Credentials

Access to Bavaria's WCS service requires authentication. To obtain credentials:

1. Register at geodaten.bayern.de
2. Subscribe to the INSPIRE elevation service
3. Use your credentials with this tool

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Troubleshooting

WCS Download Fails

• Check credentials: Ensure LDBV_USER and LDBV_PASS are correct
• Verify AOI: Ensure your DSM covers an area within Bavaria
• Check CRS: Input DSM should have proper CRS metadata

Alignment Issues

• Increase buffer: Try BUFFER_M = 5.0 for better edge coverage
• Check nodata values: Ensure DSM has proper nodata metadata

Memory Issues (Batch Processing)

• Process fewer files at once
• Use smaller BUFFER_M to reduce DTM coverage area

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Contributing

Contributions are welcome! Feel free to:

• Report bugs or issues
• Suggest new features
• Submit pull requests

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License

This code is provided as-is for processing elevation data. Please respect the data license (CC BY 4.0) when using DGM1 products.

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Contact

For questions about Bavaria's geodata services, visit geodaten.bayern.de