SME Analyzer

The SME (Subject Matter Expert) Analyzer (xylem-sme-analyzer) is a lightweight Python FastAPI microservice that converts DXF CAD drawings to clipped, print-ready PDF documents.

Purpose

When survey maps or floorplans need to be shared as PDFs, this service:

1. Reads the DXF file using ezdxf
2. Renders the drawing as SVG
3. Clips to a specified viewport or boundary
4. Converts SVG → PDF using CairoSVG
5. Returns the final PDF file

Architecture

xylem-sme-analyzer/
├── app/
│   ├── main.py            # FastAPI application + endpoints
│   ├── converter.py       # Core DXF → SVG → PDF conversion logic
│   └── __init__.py
├── pyproject.toml          # Dependencies (managed by uv)
└── uv.lock                # Lock file

API Endpoints

Method	Path	Description
POST	/convert	Convert a DXF file to PDF
GET	/health	Health check

Convert Endpoint

POST /convert
Content-Type: multipart/form-data

Parameters:
  - file: DXF file (multipart upload)
  - clip_bounds: Optional viewport bounds for clipping
  - page_size: Output PDF page size (A4, A3, etc.)

Returns the generated PDF as a file download.

Dependencies

Package	Purpose
fastapi	API framework
uvicorn	ASGI server
ezdxf	DXF file reading and parsing
cairosvg	SVG → PDF rendering
shapely	Geometry clipping operations

System Dependency

Package	Install	Purpose
libcairo2	sudo apt install libcairo2-dev	Required by cairocffi / cairosvg for SVG rendering

Conversion Pipeline

Input DXF File
    │
    ▼
┌─────────────────────────┐
│ 1. Parse DXF (ezdxf)    │
│    - Read entities       │
│    - Extract geometry    │
│    - Get layer info      │
└───────────┬─────────────┘
            │
            ▼
┌─────────────────────────┐
│ 2. Render to SVG        │
│    - Convert entities    │
│    - Apply styles        │
│    - Set viewport        │
└───────────┬─────────────┘
            │
            ▼
┌─────────────────────────┐
│ 3. Clip (Shapely)       │
│    - Apply clip bounds   │
│    - Trim to viewport    │
└───────────┬─────────────┘
            │
            ▼
┌─────────────────────────┐
│ 4. SVG → PDF (CairoSVG) │
│    - Render to PDF       │
│    - Set page size       │
└───────────┬─────────────┘
            │
            ▼
    Output PDF File

Deployment

Property	Value
Domain	sme.xylem.city
Port	4802
Process Manager	PM2
SSL	Let's Encrypt via Certbot

# Install dependencies
uv sync

# Start server
uv run uvicorn app.main:app --host 0.0.0.0 --port 4802 --timeout-keep-alive 300

# Or via PM2
pm2 restart xylem-sme-analyzer

Integration

The backend calls the SME Analyzer when it needs to generate PDFs from DXF files:

Backend (NestJS) ──POST /convert──▶ SME Analyzer (FastAPI)
                    (DXF file)                │
                                              ▼
                 ◀──── PDF response ──── Converted PDF

This is used in the convertToPdf.ts utility in the backend, called from the survey-maps and catalog modules.