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Treat tiny polygon holes as dust again, but accumulated separately now #134

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Treat tiny polygon holes as dust again, but accumulated separately now #134

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f294e2a
Treat tiny polygon holes as dust again, but accumulated separately now
e-n-f Aug 25, 2023
368af49
Was winding the tiny polygon holes backwards
e-n-f Aug 25, 2023
09388d4
Try simplifying again after cleaning polygons
e-n-f Aug 25, 2023
e8236aa
Merge remote-tracking branch 'origin/main' into tiny-polygon-holes
e-n-f Aug 25, 2023
87b83d8
Treat tiny polygon reduction as a reason to extend zooms
e-n-f Aug 25, 2023
93d77d3
Post-cleaning resimplification is too disruptive
e-n-f Aug 25, 2023
ecd71fd
More commenting to stop confusing myself about hole logic
e-n-f Aug 25, 2023
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34 changes: 29 additions & 5 deletions geometry.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -186,7 +186,7 @@ void check_polygon(drawvec &geom) {
}
}

drawvec reduce_tiny_poly(drawvec &geom, int z, int detail, bool *reduced, double *accum_area, serial_feature *this_feature, serial_feature *tiny_feature) {
drawvec reduce_tiny_poly(drawvec &geom, int z, int detail, bool *reduced, double *accum_area, double *accum_hole, serial_feature *this_feature, serial_feature *tiny_feature) {
drawvec out;
const double pixel = (1LL << (32 - detail - z)) * (double) tiny_polygon_size;
bool includes_real = false;
Expand Down Expand Up @@ -221,7 +221,9 @@ drawvec reduce_tiny_poly(drawvec &geom, int z, int detail, bool *reduced, double
// in a tiny polygon rather than letting it represent itself,
// OR it is an inner ring and we haven't output an outer ring for it to be
// cut out of, so we are just subtracting its area from the tiny polygon
// rather than trying to deal with it geometrically
// rather than trying to deal with it geometrically (even if it is too big
// to really be considered a tiny polygon, which shouldn't happen because
// it should be smaller than its outer ring, which was considered tiny).
if ((area > 0 && area <= pixel * pixel) || (area < 0 && !included_last_outer)) {
// printf("area is only %f vs %lld so using square\n", area, pixel * pixel);

Expand All @@ -243,10 +245,32 @@ drawvec reduce_tiny_poly(drawvec &geom, int z, int detail, bool *reduced, double
included_last_outer = false;
}
}

// this is a tiny hole, and we have a real outer ring that we can cut it out of,
// so accumulate some hole, and if we have enough to be worth cutting, cut it out.
//
// these hole areas are accumulated separately rather than just decrementing
// the accumulated area, because otherwise it is possible to accumulate enough
// negative area to lose entire outer rings in the process of getting back up to 0.
else if (area < 0 && -area <= pixel * pixel && included_last_outer) {
*accum_hole -= area;
if (*accum_hole > pixel * pixel) {
// XXX use centroid;

// winding is backward from above because this is a hole
out.push_back(draw(VT_MOVETO, geom[i].x - pixel / 2, geom[i].y - pixel / 2));
out.push_back(draw(VT_LINETO, geom[i].x - pixel / 2, geom[i].y - pixel / 2 + pixel));
out.push_back(draw(VT_LINETO, geom[i].x - pixel / 2 + pixel, geom[i].y - pixel / 2 + pixel));
out.push_back(draw(VT_LINETO, geom[i].x - pixel / 2 + pixel, geom[i].y - pixel / 2));
out.push_back(draw(VT_LINETO, geom[i].x - pixel / 2, geom[i].y - pixel / 2));

includes_dust = true;

*accum_hole -= pixel * pixel;
}
}

// i.e., this ring is large enough that it gets to represent itself
// or it is a tiny hole out of a real polygon, which we are still treating
// as a real geometry because otherwise we can accumulate enough tiny holes
// that we will drop the next several outer rings getting back up to 0.
else {
// printf("area is %f so keeping instead of %lld\n", area, pixel * pixel);

Expand Down
2 changes: 1 addition & 1 deletion geometry.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -68,7 +68,7 @@ drawvec clip_point(drawvec &geom, int z, long long buffer);
drawvec clean_or_clip_poly(drawvec &geom, int z, int buffer, bool clip);
drawvec simple_clip_poly(drawvec &geom, int z, int buffer);
drawvec close_poly(drawvec &geom);
drawvec reduce_tiny_poly(drawvec &geom, int z, int detail, bool *reduced, double *accum_area, serial_feature *this_feature, serial_feature *tiny_feature);
drawvec reduce_tiny_poly(drawvec &geom, int z, int detail, bool *reduced, double *accum_area, double *accum_hole, serial_feature *this_feature, serial_feature *tiny_feature);
int clip(double *x0, double *y0, double *x1, double *y1, double xmin, double ymin, double xmax, double ymax);
drawvec clip_lines(drawvec &geom, int z, long long buffer);
drawvec stairstep(drawvec &geom, int z, int detail);
Expand Down
2 changes: 1 addition & 1 deletion tests/ne_110m_admin_0_countries/out/-z0_--tiny-polygon-size_100.json
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Original file line number Diff line number Diff line change
Expand Up @@ -161,7 +161,7 @@
,
{ "type": "Feature", "properties": { "scalerank": 1, "featurecla": "Admin-0 country", "labelrank": 3, "sovereignt": "Mozambique", "sov_a3": "MOZ", "adm0_dif": 0, "level": 2, "type": "Sovereign country", "admin": "Mozambique", "adm0_a3": "MOZ", "geou_dif": 0, "geounit": "Mozambique", "gu_a3": "MOZ", "su_dif": 0, "subunit": "Mozambique", "su_a3": "MOZ", "brk_diff": 0, "name": "Mozambique", "name_long": "Mozambique", "brk_a3": "MOZ", "brk_name": "Mozambique", "abbrev": "Moz.", "postal": "MZ", "formal_en": "Republic of Mozambique", "name_sort": "Mozambique", "mapcolor7": 4, "mapcolor8": 2, "mapcolor9": 1, "mapcolor13": 4, "pop_est": 21669278, "gdp_md_est": 18940, "pop_year": -99, "lastcensus": 2007, "gdp_year": -99, "economy": "7. Least developed region", "income_grp": "5. Low income", "wikipedia": -99, "iso_a2": "MZ", "iso_a3": "MOZ", "iso_n3": "508", "un_a3": "508", "wb_a2": "MZ", "wb_a3": "MOZ", "woe_id": -99, "adm0_a3_is": "MOZ", "adm0_a3_us": "MOZ", "adm0_a3_un": -99, "adm0_a3_wb": -99, "continent": "Africa", "region_un": "Africa", "subregion": "Eastern Africa", "region_wb": "Sub-Saharan Africa", "name_len": 10, "long_len": 10, "abbrev_len": 4, "tiny": -99, "homepart": 1 }, "geometry": { "type": "Polygon", "coordinates": [ [ [ 44.736328, -5.965754 ], [ 44.736328, -14.604847 ], [ 35.947266, -14.604847 ], [ 35.947266, -5.965754 ], [ 44.736328, -5.965754 ] ] ] } }
,
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,
{ "type": "Feature", "properties": { "scalerank": 1, "featurecla": "Admin-0 country", "labelrank": 3, "sovereignt": "Madagascar", "sov_a3": "MDG", "adm0_dif": 0, "level": 2, "type": "Sovereign country", "admin": "Madagascar", "adm0_a3": "MDG", "geou_dif": 0, "geounit": "Madagascar", "gu_a3": "MDG", "su_dif": 0, "subunit": "Madagascar", "su_a3": "MDG", "brk_diff": 0, "name": "Madagascar", "name_long": "Madagascar", "brk_a3": "MDG", "brk_name": "Madagascar", "abbrev": "Mad.", "postal": "MG", "formal_en": "Republic of Madagascar", "name_sort": "Madagascar", "mapcolor7": 6, "mapcolor8": 5, "mapcolor9": 2, "mapcolor13": 3, "pop_est": 20653556, "gdp_md_est": 20130, "pop_year": -99, "lastcensus": 1993, "gdp_year": -99, "economy": "7. Least developed region", "income_grp": "5. Low income", "wikipedia": -99, "iso_a2": "MG", "iso_a3": "MDG", "iso_n3": "450", "un_a3": "450", "wb_a2": "MG", "wb_a3": "MDG", "woe_id": -99, "adm0_a3_is": "MDG", "adm0_a3_us": "MDG", "adm0_a3_un": -99, "adm0_a3_wb": -99, "continent": "Africa", "region_un": "Africa", "subregion": "Eastern Africa", "region_wb": "Sub-Saharan Africa", "name_len": 10, "long_len": 10, "abbrev_len": 4, "tiny": -99, "homepart": 1 }, "geometry": { "type": "Polygon", "coordinates": [ [ [ 53.613281, -7.710992 ], [ 53.613281, -16.299051 ], [ 44.824219, -16.299051 ], [ 44.824219, -7.710992 ], [ 53.613281, -7.710992 ] ] ] } }
,
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