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Zero tolerance simplification in MVT export #463

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Sep 2, 2021
Merged

Zero tolerance simplification in MVT export #463

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16 changes: 8 additions & 8 deletions postgis/mvt.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1180,7 +1180,7 @@ LWGEOM *mvt_geom(LWGEOM *lwgeom, const GBOX *gbox, uint32_t extent, uint32_t buf
gridspec grid = {0, 0, 0, 0, 1, 1, 0, 0};
double width = gbox->xmax - gbox->xmin;
double height = gbox->ymax - gbox->ymin;
double resx, resy, res, fx, fy;
double fx, fy;
const uint8_t basic_type = lwgeom_get_basic_type(lwgeom);
int preserve_collapsed = LW_FALSE;
POSTGIS_DEBUG(2, "mvt_geom called");
Expand All @@ -1192,16 +1192,9 @@ LWGEOM *mvt_geom(LWGEOM *lwgeom, const GBOX *gbox, uint32_t extent, uint32_t buf
if (lwgeom_is_empty(lwgeom))
return NULL;

resx = width / extent;
resy = height / extent;
res = (resx < resy ? resx : resy)/2;
fx = extent / width;
fy = -(extent / height);

/* Remove all non-essential points (under the output resolution) */
lwgeom_remove_repeated_points_in_place(lwgeom, res);
lwgeom_simplify_in_place(lwgeom, res, preserve_collapsed);

/* If geometry has disappeared, you're done */
if (lwgeom_is_empty(lwgeom))
return NULL;
Expand All @@ -1217,6 +1210,13 @@ LWGEOM *mvt_geom(LWGEOM *lwgeom, const GBOX *gbox, uint32_t extent, uint32_t buf
/* Snap to integer precision, removing duplicate points */
lwgeom_grid_in_place(lwgeom, &grid);

/* Remove points on straight lines */
lwgeom_simplify_in_place(lwgeom, 0, preserve_collapsed);

/* Remove duplicates in multipoints */
if (lwgeom->type == MULTIPOINTTYPE)
lwgeom_remove_repeated_points_in_place(lwgeom, 0);

if (!lwgeom || lwgeom_is_empty(lwgeom))
return NULL;

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4 changes: 2 additions & 2 deletions regress/core/mvt_expected
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Original file line number Diff line number Diff line change
Expand Up @@ -45,8 +45,8 @@ PG38|
PG39|t
PG40 - ON |LINESTRING(0 10,0 0)
PG40 - OFF|LINESTRING(0 10,0 0)
PG41 - ON |LINESTRING(0 10,0 4,0 2,0 0,1 0)
PG41 - OFF|LINESTRING(0 10,0 4,0 2,0 0,1 0)
PG41 - ON |LINESTRING(0 10,0 0,1 0)
PG41 - OFF|LINESTRING(0 10,0 0,1 0)
PG42 - ON |LINESTRING(0 10,0 0,1 0)
PG42 - OFF|LINESTRING(0 10,0 0,1 0)
PG43 - ON |MULTIPOLYGON(((5 5,0 0,10 0,5 5)),((5 5,10 10,0 10,5 5)))
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