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Vince
Vince
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Could someone please explain why there is such a significant difference between the results of this query:

SELECT 
    ST_Distance(ST_Transform(previous_geom,3857), ST_Transform(current_geom,3857)) AS distance_transform_exp,
    ST_Distance(previous_geom::geography, current_geom::geography) AS distance_geometry_exp
FROM
(
    SELECT 
        ST_SetSRID(ST_MakePoint(-111.9096893, 40.7411742),4326) AS previous_geom,
        ST_SetSRID(ST_MakePoint(-111.9092079, 40.74135181),4326) AS current_geom
) points_table

Results:

 distance_transform_exp | distance_geometry_exp
+-----------------------+-----------------------
       59.6050787601899 |           45.19182216
(1 row)

I understand there would be a difference between geometric (Cartesian) calculation results and geodetic (spheroid) alas for the example points which are relatively close, the discrepancy would be expected to be negligible.

Thank you.

Could someone please explain why there is such a significant difference between the results of this query:

SELECT 
    ST_Distance(ST_Transform(previous_geom,3857), ST_Transform(current_geom,3857)) AS distance_transform_exp,
    ST_Distance(previous_geom::geography, current_geom::geography) AS distance_geometry_exp
FROM
(
    SELECT 
        ST_SetSRID(ST_MakePoint(-111.9096893, 40.7411742),4326) AS previous_geom,
        ST_SetSRID(ST_MakePoint(-111.9092079, 40.74135181),4326) AS current_geom
) points_table

Results:

 distance_transform_exp | distance_geometry_exp
+-----------------------+-----------------------
       59.6050787601899 |           45.19182216
(1 row)

I understand there would be a difference between geometric (Cartesian) calculation results and geodetic (spheroid) alas for the example points which are relatively close, the discrepancy would be expected to be negligible.

Thank you.

Could someone please explain why there is such a significant difference between the results of this query:

SELECT 
    ST_Distance(ST_Transform(previous_geom,3857), ST_Transform(current_geom,3857)) AS distance_transform_exp,
    ST_Distance(previous_geom::geography, current_geom::geography) AS distance_geometry_exp
FROM
(
    SELECT 
        ST_SetSRID(ST_MakePoint(-111.9096893, 40.7411742),4326) AS previous_geom,
        ST_SetSRID(ST_MakePoint(-111.9092079, 40.74135181),4326) AS current_geom
) points_table

Results:

 distance_transform_exp | distance_geometry_exp
+-----------------------+-----------------------
       59.6050787601899 |           45.19182216
(1 row)

I understand there would be a difference between geometric (Cartesian) calculation results and geodetic (spheroid) alas for the example points which are relatively close, the discrepancy would be expected to be negligible.

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Nona Bene
Nona Bene
  • 33
  • 3

PostGIS ST_Distance in meters discrepancy

Could someone please explain why there is such a significant difference between the results of this query:

SELECT 
    ST_Distance(ST_Transform(previous_geom,3857), ST_Transform(current_geom,3857)) AS distance_transform_exp,
    ST_Distance(previous_geom::geography, current_geom::geography) AS distance_geometry_exp
FROM
(
    SELECT 
        ST_SetSRID(ST_MakePoint(-111.9096893, 40.7411742),4326) AS previous_geom,
        ST_SetSRID(ST_MakePoint(-111.9092079, 40.74135181),4326) AS current_geom
) points_table

Results:

 distance_transform_exp | distance_geometry_exp
+-----------------------+-----------------------
       59.6050787601899 |           45.19182216
(1 row)

I understand there would be a difference between geometric (Cartesian) calculation results and geodetic (spheroid) alas for the example points which are relatively close, the discrepancy would be expected to be negligible.

Thank you.