PostGIS
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QGIS
MapBender
GeoServer
GeoNode
GeoNetwork
Novella
Solutions
89 lines
2.0 KiB
Markdown
89 lines
2.0 KiB
Markdown
# Nearest Analysis Worker
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Processes nearest neighbor analysis jobs between two datasets.
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## Overview
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The nearest analysis worker finds the nearest features from a target dataset for each feature in a source dataset.
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## Job Type
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`nearest`
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## Input Parameters
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```json
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{
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"source_dataset_id": 123,
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"target_dataset_id": 124,
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"max_distance": 5000,
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"limit": 1
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}
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```
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### Parameters
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- `source_dataset_id` (required): Source dataset ID
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- `target_dataset_id` (required): Target dataset ID
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- `max_distance` (optional): Maximum search distance in dataset units
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- `limit` (optional): Maximum neighbors per feature (default: 1)
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## Output
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Creates a new dataset with nearest neighbor results:
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- Original source feature geometry
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- Nearest target feature information
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- Distance to nearest neighbor
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- Attributes from both source and target features
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## Algorithm
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The worker uses PostGIS functions to:
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1. For each source feature, find nearest target features
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2. Calculate distances using spatial indexes
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3. Apply distance and limit constraints
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4. Join attributes from both datasets
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5. Store results in output table
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## Example
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```bash
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# Enqueue a nearest analysis job via API
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curl -X POST "https://example.com/api/nearest_run.php" \
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-H "Content-Type: application/json" \
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-d '{
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"source_dataset_id": 123,
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"target_dataset_id": 124,
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"max_distance": 5000,
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"limit": 1
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}'
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# Worker processes the job automatically
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```
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## Background Jobs
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This analysis runs as a background job. The worker:
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1. Fetches queued `nearest` jobs
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2. Validates input parameters
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3. Executes PostGIS nearest neighbor queries
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4. Creates output dataset
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5. Marks job as completed
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## Performance Considerations
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- Processing time depends on dataset sizes
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- Spatial indexes are critical for performance
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- Large max_distance values may slow processing
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- Consider limiting results per feature
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## Related Documentation
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- [Nearest Analysis Tool](../analysis-tools/nearest.md)
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- [Analysis API](../api/analysis.md)
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- [Workers Overview](index.md)
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