Lambert72 to Lambert 08

Lambert72/08
Transformation
Realign transformed geometries after Lambert72 -> Lambert08 conversion
Author

Karel Dieussaert

Published

January 14, 2026

Lambert72/08 transformation

This example shows a two-step workflow for CRS migration scenarios:

  1. Align in Lambert72 (EPSG:31370) to create a clean baseline.
  2. Transform geometry to Lambert08 (EPSG:3812) and re-align to remove transformation-induced offsets.

Why this is important

When geometries are transformed between CRS systems, small coordinate deviations can appear. A final brdr alignment step ensures boundaries follow the target reference layer precisely.

What to look at in the output

  • The final aligned Lambert08 geometry (result).
  • The corrected deviations (result_diff), which show what was adjusted after transformation.
from pyproj import Transformer
from shapely.ops import transform

from brdr.aligner import Aligner
from brdr.be.grb.enums import GRBType
from brdr.be.grb.loader import GRBActualLoader
from brdr.be.oe.enums import OEType
from brdr.be.oe.loader import OnroerendErfgoedLoader
from brdr.loader import DictLoader
from brdr.viz import show_map


def transform_geom_31370_to_3812(geom):
    """Transform a Shapely geometry from EPSG:31370 to EPSG:3812."""
    transformer = Transformer.from_crs("EPSG:31370", "EPSG:3812", always_xy=True)
    return transform(transformer.transform, geom)


if __name__ == "__main__":
    # 1) Load and align data in Lambert72 (EPSG:31370).
    aligner72 = Aligner(crs="EPSG:31370")
    print("start loading OE-objects")
    aligner72.load_thematic_data(
        OnroerendErfgoedLoader(
            objectids=["https://id.erfgoed.net/aanduidingsobjecten/121125"],
            oetype=OEType.AO,
        )
    )
    print(
        "Number of OE-thematic features loaded into base-aligner: "
        + str(len(aligner72.thematic_data.features))
    )
    aligner72.load_reference_data(
        GRBActualLoader(grb_type=GRBType.ADP, partition=1000, aligner=aligner72)
    )
    print("Reference-data loaded")

    relevant_distance_72 = 2
    aligner_result72 = aligner72.process(relevant_distances=[relevant_distance_72])
    print(
        "Processed: the data-object is now fully aligned to the reference-data in Lambert72"
    )

    # 2) Transform aligned data from Lambert72 to Lambert08.
    dict08 = {}
    print(
        "Next, we do a transformation of the data-object to Lambert08, possibly resulting in some deviations"
    )
    for key, process_result in aligner_result72.results.items():
        dict08[key] = transform_geom_31370_to_3812(
            process_result[relevant_distance_72]["result"]
        )

    # 3) Re-align transformed data in Lambert08.
    print(
        "We make a new aligner with CRS EPSG:3812 (Lambert08), so we can align the deviated object to the reference-data(Lambert08)"
    )
    aligner08 = Aligner(crs="EPSG:3812")
    aligner08.load_thematic_data(DictLoader(dict08))
    aligner08.load_reference_data(
        GRBActualLoader(grb_type=GRBType.ADP, partition=1000, aligner=aligner08)
    )

    relevant_distance_08 = 0.5
    aligner_result08 = aligner08.process(relevant_distances=[relevant_distance_08])
    for _, process_result in aligner_result08.results.items():

        print(
            "Resulting aligned geometry (Lambert08): "
            + process_result[relevant_distance_08]["result"].wkt
        )
        print(
            "Corrected deviations (Lambert08): "
            + process_result[relevant_distance_08]["result_diff"].wkt
        )

    thematic_geometries = {
        key: feat.geometry for key, feat in aligner08.thematic_data.features.items()
    }
    reference_geometries = {
        key: feat.geometry for key, feat in aligner08.reference_data.features.items()
    }
    show_map(aligner_result08.results, thematic_geometries, reference_geometries)
start loading OE-objects
Number of OE-thematic features loaded into base-aligner: 1
Reference-data loaded
Processed: the data-object is now fully aligned to the reference-data in Lambert72
Next, we do a transformation of the data-object to Lambert08, possibly resulting in some deviations
We make a new aligner with CRS EPSG:3812 (Lambert08), so we can align the deviated object to the reference-data(Lambert08)
Resulting aligned geometry (Lambert08): POLYGON ((625098.7473393852 680525.1911945271, 625098.2218593401 680526.3664113319, 625098.177706751 680526.4651569742, 625095.28323862 680525.04495726, 625090.5339789229 680522.7146866346, 625081.10584485 680518.0896043903, 625080.2064425997 680523.11042433, 625079.3794076596 680527.72722602, 625078.8939072996 680530.43740507, 625078.2542584303 680534.00841862, 625077.60525949 680537.6315263597, 625077.0639787512 680540.6529269469, 625077.0433572497 680540.76889077, 625073.7535124507 680540.30846709, 625073.5482787762 680540.2050840257, 625071.3089371707 680539.07682732, 625071.0651950274 680539.888627599, 625071.0534785206 680539.928177442, 625058.3830996397 680582.2375343892, 625042.18167683 680576.1780529297, 625028.0450691179 680604.8713687307, 625030.0914488839 680605.4420033552, 625038.9673750077 680607.918010264, 625039.7678556138 680608.1413104001, 625039.7995553301 680608.1501532793, 625072.7417162794 680617.3396189411, 625084.1533328403 680620.5229759387, 625117.0412757118 680629.6969620653, 625124.1793480635 680564.1786487388, 625108.1413849437 680555.876637919, 625109.2966578461 680545.2685593922, 625110.40259653 680545.42284679, 625110.6027167804 680542.2198393703, 625110.83143457 680538.5610331503, 625111.0601522904 680534.9029309197, 625111.1885855496 680532.84908433, 625111.2312894705 680532.1658395426, 625111.3483120464 680530.2942735956, 625098.7473393852 680525.1911945271))
Corrected deviations (Lambert08): MULTIPOLYGON (((625111.3182642603 680530.2821049932, 625111.2086993367 680532.0343743499, 625111.1659951264 680532.7176140873, 625111.0375595295 680534.7714689089, 625110.808837501 680538.4295883679, 625110.5801153713 680542.0884120895, 625110.3799913554 680545.2914343103, 625109.310416747 680545.1422208368, 625109.2966578453 680545.2685593921, 625110.40259653 680545.42284679, 625110.6027167804 680542.2198393703, 625110.83143457 680538.5610331503, 625111.0601522904 680534.9029309197, 625111.1885855496 680532.84908433, 625111.2312894705 680532.1658395426, 625111.3483120464 680530.2942735956, 625111.3182642603 680530.2821049932)), ((625042.18167683 680576.1780529297, 625058.3830996397 680582.2375343892, 625071.0534785206 680539.928177442, 625071.0651950274 680539.888627599, 625071.3089371707 680539.07682732, 625073.5482782001 680540.2050837354, 625073.7535124507 680540.30846709, 625077.0433572497 680540.76889077, 625077.0639787512 680540.6529269469, 625077.60525949 680537.6315263597, 625078.2542584303 680534.00841862, 625078.8939072996 680530.43740507, 625079.3794076596 680527.72722602, 625080.2064425997 680523.11042433, 625081.10584485 680518.0896043903, 625090.5339787827 680522.7146865658, 625095.28323862 680525.04495726, 625098.177706751 680526.4651569742, 625098.22185934 680526.3664113322, 625095.2606841647 680524.9134760932, 625090.5114342512 680522.5832021107, 625081.0833221747 680517.9581145948, 625080.1839151406 680522.9789592265, 625079.3568756661 680527.5957837077, 625078.871372633 680530.3059761532, 625078.2317202648 680533.8770073362, 625077.5827177647 680537.5001329893, 625077.041434098 680540.521548292, 625077.0208124437 680540.6375129187, 625073.730973594 680540.1770926312, 625073.5257411728 680540.073709828, 625071.2864038679 680538.9454512311, 625071.0426610925 680539.7572556819, 625071.0309444739 680539.7968059701, 625058.3605326456 680582.1063814665, 625042.1591440777 680576.0468996338, 625027.9685043712 680604.8500185898, 625028.0450691181 680604.8713687302, 625042.18167683 680576.1780529297)))

Alignment after Lambert72/08-transformation

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