python - distance from a point to the nearest edge of a polygon

Question

in the below code i want to calculate the distance from a point to the nearest edge of a polygon.as shown in the results section below, the coordinates are provided.the code posted below shows how i find the distance from a point to the neatrest edge of a polygon. at run time, and as shown below in restults section, for the give point and geometry, the distance from postgis is equal to 4.32797817574802 while the one calculated from geopandas gives 3.8954865274727614e-05

please let me know how to find the distance from a point to nearest edge of a polygon.

code

poly = wkt.loads(fieldCoordinatesAsTextInWKTInEPSG25832)
pt = wkt.loads(centerPointointAsTextInWKTInEPSG25832)
print(poly.distance(pt)))

results:

queryPostgreSQLForDistancesFromPointsToPolygon:4.32797817574802#result from postgis using st_distance operator
centerPointointAsTextInWKTInEPSG4326:POINT(6.7419520458647835 51.08427961641239)
centerPointointAsTextInWKTInEPSG25832:POINT(341849.5 5661622.5)
centerPointointAsTextInWKTInEPSG4326:POINT(6.7419520458647835 51.08427961641239)
fieldCoordinatesAsTextInWKTInEPSG25832:POLYGON ((5622486.93624152 1003060.89945681,5622079.52632924 1003170.95198635,5622126.00418918 1003781.73122161,5622444.73987453 1003694.55868486,5622486.93624152 1003060.89945681))
fieldCoordinatesAsTextInWKTInEPSG4326:POLYGON((6.741879696309871 51.08423775429969,6.742907378503366 51.08158745820981,6.746964018740842 51.08233499299334,6.746152690693346 51.08440763989611,6.741879696309871 51.08423775429969))
poly.distance(pt):3.8954865274727614e-05#result from geopandas

Answer 1

• your code works. It's approx 7000km from Belgium to Ethiopia
• are you sure your data is correct? Have built a plotly graph to show where buffered polygon, polygon centroid and point are located in EPSG:4326 CRS

from shapely import wkt
import geopandas as gpd
import plotly.express as px
import json

# queryPostgreSQLForDistancesFromPointsToPolygon:4.32797817574802#result from postgis using st_distance operator
centerPointointAsTextInWKTInEPSG4326 = "POINT(6.7419520458647835 51.08427961641239)"
centerPointointAsTextInWKTInEPSG25832 = "POINT(341849.5 5661622.5)"
centerPointointAsTextInWKTInEPSG4326 = "POINT(6.7419520458647835 51.08427961641239)"
fieldCoordinatesAsTextInWKTInEPSG25832 = "POLYGON ((5622486.93624152 1003060.89945681,5622079.52632924 1003170.95198635,5622126.00418918 1003781.73122161,5622444.73987453 1003694.55868486,5622486.93624152 1003060.89945681))"
fieldCoordinatesAsTextInWKTInEPSG4326 = "POLYGON((6.741879696309871 51.08423775429969,6.742907378503366 51.08158745820981,6.746964018740842 51.08233499299334,6.746152690693346 51.08440763989611,6.741879696309871 51.08423775429969))"
# poly.distance(pt):3.8954865274727614e-05#result from geopandas

poly = wkt.loads(fieldCoordinatesAsTextInWKTInEPSG25832)
pt = wkt.loads(centerPointointAsTextInWKTInEPSG25832)

print(poly.distance(pt)/10**3)

# let's visualize it....
gpoly = (
    gpd.GeoDataFrame(geometry=[poly], crs="EPSG:25832")
    .buffer(10 ** 6)
    .to_crs("EPSG:4326")
)
gpoly.plot()
gpt = gpd.GeoDataFrame(geometry=[pt, poly.centroid], crs="EPSG:25832").to_crs(
    "EPSG:4326"
)
px.scatter_mapbox(
    gpt.assign(dist=poly.distance(pt)/10**3),
    lat=gpt.geometry.y,
    lon=gpt.geometry.x,
    hover_data={"dist":":.0f"},
).update_layout(
    mapbox={
        "style": "carto-positron",
        "zoom": 4,
        "layers": [
            {
                "source": json.loads(gpoly.to_json()),
                "below": "traces",
                "type": "fill",
                "color": "red",
            }
        ],
    }
)