From bd1f6a09398fea3b0cf6f6fda0a1ba09f34ec21e Mon Sep 17 00:00:00 2001
From: Erica Fischer <enf@felt.com>
Date: Wed, 14 Dec 2022 12:45:38 -0800
Subject: [PATCH] Add an option to adjust the -rp drop rate

---
 CHANGELOG.md     |  1 +
 README.md        |  3 ++-
 main.cpp         | 17 ++++++++++++++++-
 man/tippecanoe.1 |  3 ++-
 4 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3aba60aa..10f80405 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,7 @@
 
 * Make as-needed dropping and coalescing much faster: Don't keep scanning through the whole layer looking for another small feature.
 * Don't guess an excessively large maxzoom when there is only one feature
+* Add an option to adjust the -rp drop rate
 
 ## 2.15.2
 
diff --git a/README.md b/README.md
index 41f40e28..4f9b94ba 100644
--- a/README.md
+++ b/README.md
@@ -448,7 +448,8 @@ the same layer, enclose them in an `all` expression so they will all be evaluate
    You can also specify a marker-width with `-rg`*width* to allow fewer features in the densest tile to
    compensate for the larger marker, or `-rf`*number* to allow at most *number* features in the densest tile.
    If you use `-rp` with `-zg` or `--smallest-maximum-zoom-guess` it will choose a drop rate from the same
-   distance-between-features metrics as are used to choose the maxzoom.
+   distance-between-features metrics as are used to choose the maxzoom. If you use `-rp`*multiplier* it will keep
+   *multiplier* times as many points in zoom level 0 as it would normally choose.
  * `-B` _zoom_ or `--base-zoom=`_zoom_: Base zoom, the level at and above which all points are included in the tiles (default maxzoom).
    If you use `-Bg`, it will guess a zoom level that will keep at most 50,000 features in the densest tile.
    You can also specify a marker-width with `-Bg`*width* to allow fewer features in the densest tile to
diff --git a/main.cpp b/main.cpp
index 9a6d30a5..7f1ad1ca 100644
--- a/main.cpp
+++ b/main.cpp
@@ -86,6 +86,7 @@ std::string attribute_for_id = "";
 size_t limit_tile_feature_count = 0;
 size_t limit_tile_feature_count_at_maxzoom = 0;
 unsigned int drop_denser = 0;
+double drop_rate_multiplier = 1;
 
 std::vector<order_field> order_by;
 bool order_reverse;
@@ -2165,6 +2166,12 @@ int read_input(std::vector<source> &sources, char *fname, int maxzoom, int minzo
 				if (!quiet) {
 					fprintf(stderr, "Choosing a drop rate of %f\n", droprate);
 				}
+
+				droprate /= exp(log(drop_rate_multiplier) / maxzoom);
+
+				if (drop_rate_multiplier != 1 && !quiet) {
+					fprintf(stderr, "Adjusting drop rate to %f with multiplier\n", droprate);
+				}
 			}
 		}
 
@@ -3185,8 +3192,16 @@ int main(int argc, char **argv) {
 		case 'r':
 			if (strcmp(optarg, "g") == 0) {
 				droprate = -2;
-			} else if (strcmp(optarg, "p") == 0) {
+			} else if (optarg[0] == 'p') {
 				droprate = -3;
+
+				if (optarg[1] != '\0') {
+					drop_rate_multiplier = atof_require(optarg + 1, "Drop rate multiplier");
+					if (drop_rate_multiplier <= 0) {
+						fprintf(stderr, "%s: Must specify positive multiplier >0 with -r%c\n", argv[0], optarg[0]);
+						exit(EXIT_ARGS);
+					}
+				}
 			} else if (optarg[0] == 'g' || optarg[0] == 'f') {
 				droprate = -2;
 				if (optarg[0] == 'g') {
diff --git a/man/tippecanoe.1 b/man/tippecanoe.1
index 7858d3ca..ee6eac85 100644
--- a/man/tippecanoe.1
+++ b/man/tippecanoe.1
@@ -560,7 +560,8 @@ If you use \fB\fC\-rg\fR, it will guess a drop rate that will keep at most 50,00
 You can also specify a marker\-width with \fB\fC\-rg\fR\fIwidth\fP to allow fewer features in the densest tile to
 compensate for the larger marker, or \fB\fC\-rf\fR\fInumber\fP to allow at most \fInumber\fP features in the densest tile.
 If you use \fB\fC\-rp\fR with \fB\fC\-zg\fR or \fB\fC\-\-smallest\-maximum\-zoom\-guess\fR it will choose a drop rate from the same
-distance\-between\-features metrics as are used to choose the maxzoom.
+distance\-between\-features metrics as are used to choose the maxzoom. If you use \fB\fC\-rp\fR\fImultiplier\fP it will keep
+\fImultiplier\fP times as many points in zoom level 0 as it would normally choose.
 .IP \(bu 2
 \fB\fC\-B\fR \fIzoom\fP or \fB\fC\-\-base\-zoom=\fR\fIzoom\fP: Base zoom, the level at and above which all points are included in the tiles (default maxzoom).
 If you use \fB\fC\-Bg\fR, it will guess a zoom level that will keep at most 50,000 features in the densest tile.