Fix LGU CRS

The Fix LGU CRS tool batch-corrects or repositions vector layers digitized in local arbitrary grid coordinates (~0 to ~100,000) to true WGS84 coordinates (EPSG:4326). It fits a 2D Affine transformation matrix via Ordinary Least Squares (OLS) based on control points and transforms all geometry vertices to standard WGS 84.

Access

• Processing Toolbox: GMD Pipeline → 1Map → Fix LGU CRS
• Algorithm ID: gmd_pipeline:fixlgucrs

Layer Roles & Setup

Role	Layer Parameter	Description
Input Local Grid Layer	Input Local Grid Layer (LGU Layer)	Local arbitrary grid layer (LGU layer) digitized in ~0 to ~100,000 coordinates to be repositioned
Reference Layer	Reference WGS84 Layer (_bgy / Control Points)	Standard WGS84 reference layer (e.g. 02934_bgy in EPSG:4326) providing target control point coordinates

Parameters

Inputs

Parameter	Type	Description
Input Local Grid Layer (LGU Layer)	Feature Source (Any Geometry)	Local grid layer to be corrected
Reference WGS84 Layer (_bgy / Control Points)	Feature Source (Any Geometry)	Reference layer in EPSG:4326 used for target coordinates (e.g. 02934_bgy)
Local X Field	Field (Numeric)	Optional manual selection for Local X field (overrides auto-detection)
Local Y Field	Field (Numeric)	Optional manual selection for Local Y field (overrides auto-detection)
WGS84 Longitude Field	Field (Numeric)	Optional manual selection for WGS84 Longitude field (overrides auto-detection)
WGS84 Latitude Field	Field (Numeric)	Optional manual selection for WGS84 Latitude field (overrides auto-detection)
Input Match Field	Field (Any)	Optional manual attribute field from the input layer used to match reference features
Reference Match Field	Field (Any)	Optional manual attribute field from the reference layer used to match input features

Outputs

Output	Type	Description
Corrected Layer	Feature Sink	The transformed geometry layer in EPSG:4326

How It Works

1. Smart Cross-Column Attribute & Feature Matching:

   • Evaluates cross-column candidate pairs across layers, supporting common LGU and PSA/DENR reference headers (geocode, bgy_geocode, psgc_bgy, psgc, bgy_code, brgy_code, code, barangay_n, barangay_name, bgy_name, brgy_name, name, barangay, bgy, bgy_id, adm4_en, id, fid).
   • Normalizes digit-based PSGC geocodes automatically (e.g. matching 9-digit local codes like 02934001 with 14-digit PSGC geocodes like 02934001000000).
   • Automatically selects the candidate attribute pair yielding the maximum number of unique matched control points (minimum 3).
   • Pre-computes relative spatial centroid proximity mapping as a fallback if attribute matching is partial or unavailable.

2. Coordinate Extraction:

   • Automatically auto-detects XI, YI, LongitudeI, LatitudeI fields if present in input feature attributes.
   • Falls back to feature geometry centroids for local $(X,Y)$ if local coordinate columns are absent.
   • Maps WGS84 target coordinates from matched features in the _bgy reference layer.

3. 2D Affine OLS Matrix Computation:

   • Fits a 2D affine transformation matrix via Ordinary Least Squares:$$\text{Longitude}=a\cdot X+b\cdot Y+c$$$$\text{Latitude}=d\cdot X+e\cdot Y+f$$
   • Auto-corrects swapped axis orientation (X/Y diagonal inversion) if necessary.

4. Residual Reporting & Transformation:

   • Filters outlier control points if sample size $N>4$.
   • Reports fitted transformation matrix and maximum Euclidean residual errors in the QGIS Processing Log.
   • Transforms all vertices to EPSG:4326 (WGS 84).

Supported Geometry Types

The tool handles all vector geometry types:

• Point and MultiPoint
• LineString and MultiLineString
• Polygon and MultiPolygon

Quick Setup Tip

Select your LGU layer as Input Local Grid Layer (LGU Layer) and your _bgy layer as Reference WGS84 Layer (_bgy / Control Points). The tool automatically cross-matches fields like geocode or barangay_n across both layers!