# Helsinki Solar Mapper - Data Sources

## 1. Helsinki 3D City Model (Primary)

**Source:** Helsinki Region Infoshare (HRI)
**URL:** https://hri.fi/data/en_GB/dataset/helsingin-3d-kaupunkimalli
**License:** CC BY 4.0

### City Information Model (CityGML)
- **LoD1:** Flat-roofed buildings (simpler)
- **LoD2:** Differentiated roof structures (ideal for solar analysis)
- **Format:** CityGML 2.0
- **Coordinate System:** ETRS-GK25 (plane) + N2000 (height)
- **Building IDs:** GMLID, RATU, VTJ-PRT

### Download Options
1. **Interactive:** https://kartta.hel.fi/3d/ (select area, format, textured/untextured)
2. **WFS API:** https://kartta.hel.fi/3d/citydb-wfs/wfs (version 2.0.0)

### Existing Energy Data!
**Helsinki Energy and Climate Atlas:** https://kartta.hel.fi/3d/atlas
- Building basic + energy information
- Heating energy consumption estimates (2020-2050)
- District heating, electricity, water consumption data
- Documentation: https://www.hel.fi/hel2/tietokeskus/data/dokumentit/data_atlas.pdf

## 2. FMI Solar Irradiance Data

**Source:** Finnish Meteorological Institute (FMI)
**URL:** https://en.ilmatieteenlaitos.fi/open-data

### Key Parameters Needed
- Global Horizontal Irradiance (GHI)
- Direct Normal Irradiance (DNI)
- Diffuse Horizontal Irradiance (DHI)
- Cloud cover statistics
- Historical averages (10+ years)

### Helsinki Solar Statistics (approximate)
- Annual GHI: ~950 kWh/m²
- Peak month (June): ~180 kWh/m²
- Low month (December): ~5 kWh/m²
- Daylight variation: 6h (Dec) to 19h (June)

## 3. Reality Mesh (Optional - Visualization)

**URL:** https://kartta.hel.fi/3d/mesh
- Photorealistic but not semantic
- Good for visual presentations
- Formats: OBJ, 3MX, 3SM

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## Architecture Decision

Since Helsinki Energy Atlas already exists, our app can:
1. **Complement** it with better solar-specific analysis
2. **Use same data sources** for consistency
3. **Focus on:** Roof-level detail, shading, economic analysis