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Don't swap attributes when reducing tiny polygon dust (#207)
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* Don't swap attributes when reducing tiny polygon dust

Because the dust placeholder may be misleadingly far from the feature
that contributed the most area to it

* Remove unused arguments; update changelog
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@e-n-f
e-n-f authored Feb 26, 2024
1 parent 2b6630c commit a987197
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Showing 7 changed files with 35 additions and 59 deletions.
4 changes: 4 additions & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
@@ -1,3 +1,7 @@
# 2.46.0

* Polygon dust returns to having the attributes of the contributing feature nearest the placeholder instead of the contributing feature with the largest area.

# 2.45.0

* Adjust tile size limit with --retain-points-multiplier dynamically within each tile, to allow multiplier features at high zooms if other features are being dropped as-needed
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28 changes: 1 addition & 27 deletions geometry.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -168,11 +168,9 @@ void check_polygon(drawvec &geom) {
}
}

drawvec reduce_tiny_poly(drawvec const &geom, int z, int detail, bool *still_needs_simplification, bool *reduced_away, double *accum_area, serial_feature *this_feature, serial_feature *tiny_feature) {
drawvec reduce_tiny_poly(drawvec const &geom, int z, int detail, bool *still_needs_simplification, bool *reduced_away, double *accum_area) {
drawvec out;
const double pixel = (1LL << (32 - detail - z)) * (double) tiny_polygon_size;
bool includes_real = false;
bool includes_dust = false;

bool included_last_outer = false;
*still_needs_simplification = false;
Expand Down Expand Up @@ -217,7 +215,6 @@ drawvec reduce_tiny_poly(drawvec const &geom, int z, int detail, bool *still_nee
out.emplace_back(VT_LINETO, geom[i].x - pixel / 2 + pixel, geom[i].y - pixel / 2 + pixel);
out.emplace_back(VT_LINETO, geom[i].x - pixel / 2, geom[i].y - pixel / 2 + pixel);
out.emplace_back(VT_LINETO, geom[i].x - pixel / 2, geom[i].y - pixel / 2);
includes_dust = true;

*accum_area -= pixel * pixel;
}
Expand All @@ -238,7 +235,6 @@ drawvec reduce_tiny_poly(drawvec const &geom, int z, int detail, bool *still_nee
// which means that the overall polygon has a real geometry,
// which means that it gets to be simplified.
*still_needs_simplification = true;
includes_real = true;

if (area > 0) {
included_last_outer = true;
Expand All @@ -260,28 +256,6 @@ drawvec reduce_tiny_poly(drawvec const &geom, int z, int detail, bool *still_nee
fprintf(stderr, "\n");

out.push_back(geom[i]);
includes_real = true;
}
}

if (!includes_real) {
if (includes_dust) {
// this geometry is just dust, so if there is another feature that
// contributed to the dust that is larger than this feature,
// keep its attributes instead of this one that just happened to be
// the one that hit the threshold of survival.

if (tiny_feature->extent > this_feature->extent) {
*this_feature = *tiny_feature;
tiny_feature->extent = 0;
}
} else {
// this is a feature that we are throwing away, so hang on to it
// attributes if it is bigger than the biggest one we threw away so far

if (this_feature->extent > tiny_feature->extent) {
*tiny_feature = *this_feature;
}
}
}

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2 changes: 1 addition & 1 deletion geometry.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -74,7 +74,7 @@ drawvec remove_noop(drawvec geom, int type, int shift);
drawvec clip_point(drawvec &geom, int z, long long buffer);
drawvec clean_or_clip_poly(drawvec &geom, int z, int buffer, bool clip, bool try_scaling);
drawvec close_poly(drawvec &geom);
drawvec reduce_tiny_poly(const drawvec &geom, int z, int detail, bool *still_needs_simplification, bool *reduced_away, double *accum_area, serial_feature *this_feature, serial_feature *tiny_feature);
drawvec reduce_tiny_poly(const drawvec &geom, int z, int detail, bool *still_needs_simplification, bool *reduced_away, double *accum_area);
int clip(long long *x0, long long *y0, long long *x1, long long *y1, long long xmin, long long ymin, long long xmax, long long ymax);
drawvec clip_lines(drawvec &geom, int z, long long buffer);
drawvec stairstep(drawvec &geom, int z, int detail);
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42 changes: 21 additions & 21 deletions ...10m_admin_0_countries/out/-z0_--tiny-polygon-size_50_--order-largest-first.json
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Large diffs are not rendered by default.

12 changes: 6 additions & 6 deletions tests/single-polygons/out/-Z21_-zg_-D10_-d10.json
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Expand Up @@ -15,21 +15,21 @@
}, "features": [
{ "type": "FeatureCollection", "properties": { "zoom": 21, "x": 2066402, "y": 1282091 }, "features": [
{ "type": "FeatureCollection", "properties": { "layer": "in", "version": 2, "extent": 1024 }, "features": [
{ "type": "Feature", "properties": { "seq": 7 }, "geometry": { "type": "Polygon", "coordinates": [ [ [ 174.721520, -37.166209 ], [ 174.721520, -37.166210 ], [ 174.721519, -37.166210 ], [ 174.721519, -37.166209 ], [ 174.721520, -37.166209 ] ] ] } }
{ "type": "Feature", "properties": { "seq": 9 }, "geometry": { "type": "Polygon", "coordinates": [ [ [ 174.721520, -37.166209 ], [ 174.721520, -37.166210 ], [ 174.721519, -37.166210 ], [ 174.721519, -37.166209 ], [ 174.721520, -37.166209 ] ] ] } }
,
{ "type": "Feature", "properties": { "seq": 10 }, "geometry": { "type": "Polygon", "coordinates": [ [ [ 174.721520, -37.166209 ], [ 174.721520, -37.166210 ], [ 174.721520, -37.166210 ], [ 174.721520, -37.166209 ], [ 174.721520, -37.166209 ] ] ] } }
,
{ "type": "Feature", "properties": { "seq": 11 }, "geometry": { "type": "Polygon", "coordinates": [ [ [ 174.721521, -37.166209 ], [ 174.721521, -37.166210 ], [ 174.721521, -37.166210 ], [ 174.721521, -37.166209 ], [ 174.721521, -37.166209 ] ] ] } }
,
{ "type": "Feature", "properties": { "seq": 12 }, "geometry": { "type": "Polygon", "coordinates": [ [ [ 174.721523, -37.166209 ], [ 174.721523, -37.166210 ], [ 174.721523, -37.166210 ], [ 174.721523, -37.166209 ], [ 174.721523, -37.166209 ] ] ] } }
{ "type": "Feature", "properties": { "seq": 13 }, "geometry": { "type": "Polygon", "coordinates": [ [ [ 174.721523, -37.166209 ], [ 174.721523, -37.166210 ], [ 174.721523, -37.166210 ], [ 174.721523, -37.166209 ], [ 174.721523, -37.166209 ] ] ] } }
,
{ "type": "Feature", "properties": { "seq": 16 }, "geometry": { "type": "Polygon", "coordinates": [ [ [ 174.721526, -37.166210 ], [ 174.721526, -37.166210 ], [ 174.721525, -37.166210 ], [ 174.721525, -37.166210 ], [ 174.721526, -37.166210 ] ] ] } }
,
{ "type": "Feature", "properties": { "seq": 17 }, "geometry": { "type": "Polygon", "coordinates": [ [ [ 174.721527, -37.166210 ], [ 174.721527, -37.166210 ], [ 174.721526, -37.166210 ], [ 174.721526, -37.166210 ], [ 174.721527, -37.166210 ] ] ] } }
,
{ "type": "Feature", "properties": { "seq": 18 }, "geometry": { "type": "Polygon", "coordinates": [ [ [ 174.721535, -37.166210 ], [ 174.721535, -37.166210 ], [ 174.721535, -37.166210 ], [ 174.721535, -37.166210 ], [ 174.721535, -37.166210 ] ] ] } }
{ "type": "Feature", "properties": { "seq": 19 }, "geometry": { "type": "Polygon", "coordinates": [ [ [ 174.721535, -37.166210 ], [ 174.721535, -37.166210 ], [ 174.721535, -37.166210 ], [ 174.721535, -37.166210 ], [ 174.721535, -37.166210 ] ] ] } }
,
{ "type": "Feature", "properties": { "seq": 20 }, "geometry": { "type": "Polygon", "coordinates": [ [ [ 174.721538, -37.166210 ], [ 174.721538, -37.166210 ], [ 174.721538, -37.166210 ], [ 174.721538, -37.166210 ], [ 174.721538, -37.166210 ] ] ] } }
{ "type": "Feature", "properties": { "seq": 21 }, "geometry": { "type": "Polygon", "coordinates": [ [ [ 174.721538, -37.166210 ], [ 174.721538, -37.166210 ], [ 174.721538, -37.166210 ], [ 174.721538, -37.166210 ], [ 174.721538, -37.166210 ] ] ] } }
,
{ "type": "Feature", "properties": { "seq": 22 }, "geometry": { "type": "Polygon", "coordinates": [ [ [ 174.721540, -37.166210 ], [ 174.721540, -37.166210 ], [ 174.721540, -37.166210 ], [ 174.721540, -37.166210 ], [ 174.721540, -37.166210 ] ] ] } }
,
Expand All @@ -45,7 +45,7 @@
,
{ "type": "Feature", "properties": { "seq": 30 }, "geometry": { "type": "Polygon", "coordinates": [ [ [ 174.721549, -37.166210 ], [ 174.721549, -37.166210 ], [ 174.721549, -37.166210 ], [ 174.721549, -37.166210 ], [ 174.721549, -37.166210 ] ] ] } }
,
{ "type": "Feature", "properties": { "seq": 29 }, "geometry": { "type": "Polygon", "coordinates": [ [ [ 174.721557, -37.166210 ], [ 174.721557, -37.166210 ], [ 174.721557, -37.166210 ], [ 174.721557, -37.166210 ], [ 174.721557, -37.166210 ] ] ] } }
{ "type": "Feature", "properties": { "seq": 32 }, "geometry": { "type": "Polygon", "coordinates": [ [ [ 174.721557, -37.166210 ], [ 174.721557, -37.166210 ], [ 174.721557, -37.166210 ], [ 174.721557, -37.166210 ], [ 174.721557, -37.166210 ] ] ] } }
,
{ "type": "Feature", "properties": { "seq": 33 }, "geometry": { "type": "Polygon", "coordinates": [ [ [ 174.721559, -37.166210 ], [ 174.721559, -37.166210 ], [ 174.721558, -37.166210 ], [ 174.721558, -37.166210 ], [ 174.721559, -37.166210 ] ] ] } }
,
Expand All @@ -69,7 +69,7 @@
,
{ "type": "Feature", "properties": { "seq": 13 }, "geometry": { "type": "Polygon", "coordinates": [ [ [ 174.721524, -37.166210 ], [ 174.721524, -37.166210 ], [ 174.721524, -37.166210 ], [ 174.721523, -37.166210 ], [ 174.721524, -37.166210 ] ] ] } }
,
{ "type": "Feature", "properties": { "seq": 6 }, "geometry": { "type": "Polygon", "coordinates": [ [ [ 174.721524, -37.166210 ], [ 174.721524, -37.166210 ], [ 174.721524, -37.166210 ], [ 174.721524, -37.166210 ], [ 174.721524, -37.166210 ] ] ] } }
{ "type": "Feature", "properties": { "seq": 14 }, "geometry": { "type": "Polygon", "coordinates": [ [ [ 174.721524, -37.166210 ], [ 174.721524, -37.166210 ], [ 174.721524, -37.166210 ], [ 174.721524, -37.166210 ], [ 174.721524, -37.166210 ] ] ] } }
,
{ "type": "Feature", "properties": { "seq": 15 }, "geometry": { "type": "Polygon", "coordinates": [ [ [ 174.721525, -37.166210 ], [ 174.721525, -37.166210 ], [ 174.721525, -37.166210 ], [ 174.721525, -37.166210 ], [ 174.721525, -37.166210 ] ] ] } }
,
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4 changes: 1 addition & 3 deletions tile.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1591,8 +1591,6 @@ long long write_tile(decompressor *geoms, std::atomic<long long> *geompos_in, ch
FILE *prefilter_read_fp = NULL;
json_pull *prefilter_jp = NULL;

serial_feature tiny_feature; // used to track which feature currently represents the dust

if (z < minzoom) {
prefilter = NULL;
postfilter = NULL;
Expand Down Expand Up @@ -1852,7 +1850,7 @@ long long write_tile(decompressor *geoms, std::atomic<long long> *geompos_in, ch
bool prevent_tiny = prevent[P_TINY_POLYGON_REDUCTION] ||
(prevent[P_TINY_POLYGON_REDUCTION_AT_MAXZOOM] && z == maxzoom);
if (!prevent_tiny && !additional[A_GRID_LOW_ZOOMS]) {
sf.geometry = reduce_tiny_poly(sf.geometry, z, line_detail, &still_need_simplification_after_reduction, &simplified_away_by_reduction, &accum_area, &sf, &tiny_feature);
sf.geometry = reduce_tiny_poly(sf.geometry, z, line_detail, &still_need_simplification_after_reduction, &simplified_away_by_reduction, &accum_area);
if (simplified_away_by_reduction) {
strategy->tiny_polygons++;
}
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2 changes: 1 addition & 1 deletion version.hpp
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Original file line number Diff line number Diff line change
@@ -1,6 +1,6 @@
#ifndef VERSION_HPP
#define VERSION_HPP

#define VERSION "v2.45.0"
#define VERSION "v2.46.0"

#endif

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