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PostGIS 1.5.8 Manual262 / 310DescriptionReturns Z maxima of a bounding box 2d or 3d or a geometry.NoteAlthough this function is only defined for box3d, it will work for box2d and geometry because of the auto-casting behaviordefined for geometries and box2d. However you can not feed it a geometry or box2d text represenation, since that willnot auto-cast.This function supports 3d and will not drop the z-index.This method supports Circular Strings and CurvesExamplesSELECT ST_ZMax(’BOX3D(1 2 3, 4 5 6)’);st_zmax-------6SELECT ST_ZMax(ST_GeomFromEWKT(’LINESTRING(1 3 4, 5 6 7)’));st_zmax-------7SELECT ST_ZMax(’BOX3D(-3 2 1, 3 4 1)’ );st_zmax-------1--Observe THIS DOES NOT WORK because it will try to autocast the string representation to a ←↪BOX3DSELECT ST_ZMax(’LINESTRING(1 3 4, 5 6 7)’);--ERROR:BOX3D parser - doesnt start with BOX3D(SELECT ST_ZMax(ST_GeomFromEWKT(’CIRCULARSTRING(220268 150415 1,220227 150505 2,220227150406 3)’));st_zmax--------3←↪See AlsoST_GeomFromEWKT, ST_XMin, ST_XMax, ST_YMax, ST_YMin, ST_ZMax7.12.16 ST_ZMinST_ZMin — Returns Z minima of a bounding box 2d or 3d or a geometry.Synopsisfloat ST_ZMin(box3d aGeomorBox2DorBox3D);