PostGIS function to move a polygon to centre over new point coordinates












3















Background:



(Note: I am trying to do as much of this as possible in PostGIS/PostgreSQL)



I have a PostgreSQL table containing location data of an aircraft in orbit around a city. Every second a new row is added with new position data.



From this table I have created a view which shows a constantly updating point of only the current position. This view therefore contains only one row.



The Task:



I have created a custom polygon in a different table, which acts as a buffer around the current position point. I want to reposition/move this polygon to always be centred over the constantly updating current position coordinates. Does anyone know how to do this? I have already experimented with rotate and scale. I am happy with them. It is moving the polygon that is confusing me.



I have tried creating a view that uses ST_Translate for the polygon, however from my understanding, this function only moves coordinates by a fixed amount from the origin. It doesn’t allow me to specify exactly what lon lat coordinates I want it to move to. Does anyone know a function/how to move a polygon to new coordinates, centred on a point? Again, I am trying to achieve this from PostGIS.










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  • 1





    ST_Translate moves a geometry by a specified amount in x, y and, optionally, z directions. So, to calculate how much you need to move the polygon, calculate the change in x and y between your new point and the centroid of the polygon

    – John Powell
    1 hour ago
















3















Background:



(Note: I am trying to do as much of this as possible in PostGIS/PostgreSQL)



I have a PostgreSQL table containing location data of an aircraft in orbit around a city. Every second a new row is added with new position data.



From this table I have created a view which shows a constantly updating point of only the current position. This view therefore contains only one row.



The Task:



I have created a custom polygon in a different table, which acts as a buffer around the current position point. I want to reposition/move this polygon to always be centred over the constantly updating current position coordinates. Does anyone know how to do this? I have already experimented with rotate and scale. I am happy with them. It is moving the polygon that is confusing me.



I have tried creating a view that uses ST_Translate for the polygon, however from my understanding, this function only moves coordinates by a fixed amount from the origin. It doesn’t allow me to specify exactly what lon lat coordinates I want it to move to. Does anyone know a function/how to move a polygon to new coordinates, centred on a point? Again, I am trying to achieve this from PostGIS.










share|improve this question









New contributor




Demus is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
















  • 1





    ST_Translate moves a geometry by a specified amount in x, y and, optionally, z directions. So, to calculate how much you need to move the polygon, calculate the change in x and y between your new point and the centroid of the polygon

    – John Powell
    1 hour ago














3












3








3








Background:



(Note: I am trying to do as much of this as possible in PostGIS/PostgreSQL)



I have a PostgreSQL table containing location data of an aircraft in orbit around a city. Every second a new row is added with new position data.



From this table I have created a view which shows a constantly updating point of only the current position. This view therefore contains only one row.



The Task:



I have created a custom polygon in a different table, which acts as a buffer around the current position point. I want to reposition/move this polygon to always be centred over the constantly updating current position coordinates. Does anyone know how to do this? I have already experimented with rotate and scale. I am happy with them. It is moving the polygon that is confusing me.



I have tried creating a view that uses ST_Translate for the polygon, however from my understanding, this function only moves coordinates by a fixed amount from the origin. It doesn’t allow me to specify exactly what lon lat coordinates I want it to move to. Does anyone know a function/how to move a polygon to new coordinates, centred on a point? Again, I am trying to achieve this from PostGIS.










share|improve this question









New contributor




Demus is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.












Background:



(Note: I am trying to do as much of this as possible in PostGIS/PostgreSQL)



I have a PostgreSQL table containing location data of an aircraft in orbit around a city. Every second a new row is added with new position data.



From this table I have created a view which shows a constantly updating point of only the current position. This view therefore contains only one row.



The Task:



I have created a custom polygon in a different table, which acts as a buffer around the current position point. I want to reposition/move this polygon to always be centred over the constantly updating current position coordinates. Does anyone know how to do this? I have already experimented with rotate and scale. I am happy with them. It is moving the polygon that is confusing me.



I have tried creating a view that uses ST_Translate for the polygon, however from my understanding, this function only moves coordinates by a fixed amount from the origin. It doesn’t allow me to specify exactly what lon lat coordinates I want it to move to. Does anyone know a function/how to move a polygon to new coordinates, centred on a point? Again, I am trying to achieve this from PostGIS.







qgis postgis postgresql polygon move






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edited 1 hour ago









Vince

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14.6k32748






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asked 2 hours ago









DemusDemus

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Demus is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.






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  • 1





    ST_Translate moves a geometry by a specified amount in x, y and, optionally, z directions. So, to calculate how much you need to move the polygon, calculate the change in x and y between your new point and the centroid of the polygon

    – John Powell
    1 hour ago














  • 1





    ST_Translate moves a geometry by a specified amount in x, y and, optionally, z directions. So, to calculate how much you need to move the polygon, calculate the change in x and y between your new point and the centroid of the polygon

    – John Powell
    1 hour ago








1




1





ST_Translate moves a geometry by a specified amount in x, y and, optionally, z directions. So, to calculate how much you need to move the polygon, calculate the change in x and y between your new point and the centroid of the polygon

– John Powell
1 hour ago





ST_Translate moves a geometry by a specified amount in x, y and, optionally, z directions. So, to calculate how much you need to move the polygon, calculate the change in x and y between your new point and the centroid of the polygon

– John Powell
1 hour ago










1 Answer
1






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oldest

votes


















3














The easiest would be to have your polygon centered on (0;0) and to use st_translate using the target point X;Y as the delta X and delta Y.



Using any polygon, you would compute the delta by removing the polygon centroid X and Y from the target point X and Y:



WITH pt AS (SELECT 'point(-75.5 47.2)'::geometry geom),
poly AS (SELECT 'polygon((-70 41, -71 41, -71 40,-70 40, -70 41))'::geometry geom)
SELECT st_asText(
ST_TRANSLATE(
poly.geom,
st_x(pt.geom) - st_x(st_centroid(poly.geom)),
st_y(pt.geom) - st_y(st_centroid(poly.geom))
)
)
FROM pt, poly;

st_astext
---------------------------------------------------------
POLYGON((-75 47.7,-76 47.7,-76 46.7,-75 46.7,-75 47.7))
(1 row)





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    1 Answer
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    1 Answer
    1






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    active

    oldest

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    active

    oldest

    votes









    3














    The easiest would be to have your polygon centered on (0;0) and to use st_translate using the target point X;Y as the delta X and delta Y.



    Using any polygon, you would compute the delta by removing the polygon centroid X and Y from the target point X and Y:



    WITH pt AS (SELECT 'point(-75.5 47.2)'::geometry geom),
    poly AS (SELECT 'polygon((-70 41, -71 41, -71 40,-70 40, -70 41))'::geometry geom)
    SELECT st_asText(
    ST_TRANSLATE(
    poly.geom,
    st_x(pt.geom) - st_x(st_centroid(poly.geom)),
    st_y(pt.geom) - st_y(st_centroid(poly.geom))
    )
    )
    FROM pt, poly;

    st_astext
    ---------------------------------------------------------
    POLYGON((-75 47.7,-76 47.7,-76 46.7,-75 46.7,-75 47.7))
    (1 row)





    share|improve this answer




























      3














      The easiest would be to have your polygon centered on (0;0) and to use st_translate using the target point X;Y as the delta X and delta Y.



      Using any polygon, you would compute the delta by removing the polygon centroid X and Y from the target point X and Y:



      WITH pt AS (SELECT 'point(-75.5 47.2)'::geometry geom),
      poly AS (SELECT 'polygon((-70 41, -71 41, -71 40,-70 40, -70 41))'::geometry geom)
      SELECT st_asText(
      ST_TRANSLATE(
      poly.geom,
      st_x(pt.geom) - st_x(st_centroid(poly.geom)),
      st_y(pt.geom) - st_y(st_centroid(poly.geom))
      )
      )
      FROM pt, poly;

      st_astext
      ---------------------------------------------------------
      POLYGON((-75 47.7,-76 47.7,-76 46.7,-75 46.7,-75 47.7))
      (1 row)





      share|improve this answer


























        3












        3








        3







        The easiest would be to have your polygon centered on (0;0) and to use st_translate using the target point X;Y as the delta X and delta Y.



        Using any polygon, you would compute the delta by removing the polygon centroid X and Y from the target point X and Y:



        WITH pt AS (SELECT 'point(-75.5 47.2)'::geometry geom),
        poly AS (SELECT 'polygon((-70 41, -71 41, -71 40,-70 40, -70 41))'::geometry geom)
        SELECT st_asText(
        ST_TRANSLATE(
        poly.geom,
        st_x(pt.geom) - st_x(st_centroid(poly.geom)),
        st_y(pt.geom) - st_y(st_centroid(poly.geom))
        )
        )
        FROM pt, poly;

        st_astext
        ---------------------------------------------------------
        POLYGON((-75 47.7,-76 47.7,-76 46.7,-75 46.7,-75 47.7))
        (1 row)





        share|improve this answer













        The easiest would be to have your polygon centered on (0;0) and to use st_translate using the target point X;Y as the delta X and delta Y.



        Using any polygon, you would compute the delta by removing the polygon centroid X and Y from the target point X and Y:



        WITH pt AS (SELECT 'point(-75.5 47.2)'::geometry geom),
        poly AS (SELECT 'polygon((-70 41, -71 41, -71 40,-70 40, -70 41))'::geometry geom)
        SELECT st_asText(
        ST_TRANSLATE(
        poly.geom,
        st_x(pt.geom) - st_x(st_centroid(poly.geom)),
        st_y(pt.geom) - st_y(st_centroid(poly.geom))
        )
        )
        FROM pt, poly;

        st_astext
        ---------------------------------------------------------
        POLYGON((-75 47.7,-76 47.7,-76 46.7,-75 46.7,-75 47.7))
        (1 row)






        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered 1 hour ago









        JGHJGH

        12.4k21136




        12.4k21136






















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