{
	"transformations": [
		{
			"from": "EPSG:4277",
			"to": "EPSG:4258",
			"method": "OSTN15 grid transformation",
			"accuracy": "0.1m",
			"notes": "OSTN15 provides centimetric accuracy. Recommended method for OSGB36 to ETRS89 in Great Britain.",
			"epsgCode": "EPSG:7709",
			"reversible": true
		},
		{
			"from": "EPSG:4277",
			"to": "EPSG:4326",
			"method": "OSTN15 via ETRS89",
			"accuracy": "0.1m (within GB)",
			"notes": "Transform OSGB36 to ETRS89 using OSTN15, then null transform to WGS84.",
			"reversible": true
		},
		{
			"from": "EPSG:4258",
			"to": "EPSG:4326",
			"method": "Null transformation",
			"accuracy": "Sub-meter",
			"notes": "ETRS89 and WGS84 are practically identical for most applications. Differences at cm level due to epoch.",
			"reversible": true
		},
		{
			"from": "EPSG:27700",
			"to": "EPSG:4277",
			"method": "Inverse projection",
			"accuracy": "Exact (mathematical)",
			"notes": "BNG to OSGB36 is an exact mathematical inverse of the Transverse Mercator projection.",
			"reversible": true
		},
		{
			"from": "EPSG:4299",
			"to": "EPSG:4258",
			"method": "Polynomial transformation",
			"accuracy": "0.2m",
			"notes": "TM65 (Irish datum) to ETRS89 transformation.",
			"reversible": true
		},
		{
			"from": "EPSG:29902",
			"to": "EPSG:2157",
			"method": "via ETRS89",
			"accuracy": "0.2m",
			"notes": "Irish Grid to ITM requires transformation through ETRS89.",
			"reversible": true
		}
	],
	"hubCrs": ["EPSG:4258", "EPSG:4326", "EPSG:27700"],
	"deprecatedCrs": ["EPSG:29902"],
	"migrationPaths": {
		"EPSG:29902": {
			"recommendedTarget": "EPSG:2157",
			"reason": "Irish Grid (TM65) is superseded by Irish Transverse Mercator (ITM) for new work.",
			"notes": "ITM is based on ETRS89 and provides better accuracy for modern surveying."
		}
	},
	"datumRelationships": {
		"OSGB36_ETRS89": {
			"description": "OSGB36 to ETRS89 transformation",
			"typical_shift": "0-5 meters varying across Great Britain",
			"method": "OSTN15 grid interpolation",
			"considerations": [
				"OSTN15 is the definitive transformation",
				"Shift varies across Great Britain",
				"Maximum differences in peripheral areas",
				"7-parameter Helmert only ~5m accuracy"
			]
		},
		"ETRS89_WGS84": {
			"description": "ETRS89 and WGS84 are practically identical",
			"typical_shift": "0-1 meters",
			"method": "Null transformation or epoch adjustment",
			"considerations": [
				"For most applications, can be treated as equivalent",
				"ETRS89 is fixed to European plate",
				"WGS84 follows ITRF updates",
				"Differences accumulate over time (~2.5cm/year)"
			]
		},
		"TM65_ETRS89": {
			"description": "Irish datum TM65 to ETRS89",
			"typical_shift": "Variable, up to 1m",
			"method": "Polynomial transformation",
			"considerations": [
				"Legacy Irish data requires transformation",
				"Use official OSi transformation parameters",
				"Accuracy varies by location"
			]
		}
	}
}