Merge pull request #186 from mapbox/resolution-doc

Clarify maximum resolution in README and warning

CHANGELOG.md

@@ -1,3 +1,7 @@
+## 1.9.3
+
+* Don't get stuck in a loop trying to split up very small, very complicated polygons
+
 ## 1.9.2
 
 * Increase maximum tile size for tippecanoe-decode

README.md

@@ -87,6 +87,10 @@ Options
  * -m _detail_: Minimum detail that it will try if tiles are too big at regular detail (default 7)
  * -b _pixels_: Buffer size where features are duplicated from adjacent tiles. Units are "screen pixels"--1/256th of the tile width or height. (default 5)
 
+All internal math is done in terms of a 32-bit tile coordinate system, so 1/(2^32) of the size of Earth,
+or about 1cm, is the smallest distinguishable distance. If _maxzoom_ + _detail_ > 32, no additional
+resolution is obtained than by using a smaller _maxzoom_ or _detail_.
+
 ### Properties
 
  * -x _name_: Exclude the named properties from all features

geojson.c

@@ -2268,6 +2268,7 @@ int main(int argc, char **argv) {
 	geometry_scale = 32 - (full_detail + maxzoom);
 	if (geometry_scale < 0) {
 		geometry_scale = 0;
+		fprintf(stderr, "Full detail + maxzoom > 32, so you are asking for more detail than is available.\n");
 	}
 
 	if ((basezoom < 0 || droprate < 0) && (gamma < 0)) {

man/tippecanoe.1

@@ -102,6 +102,10 @@ compensate for the larger marker, or \-Bf\fInumber\fP to allow at most \fInumber
 .IP \(bu 2
 \-b \fIpixels\fP: Buffer size where features are duplicated from adjacent tiles. Units are "screen pixels"\-\-1/256th of the tile width or height. (default 5)
 .RE
+.PP
+All internal math is done in terms of a 32\-bit tile coordinate system, so 1/(2 of the size of Earth,
+or about 1cm, is the smallest distinguishable distance. If \fImaxzoom\fP + \fIdetail\fP > 32, no additional
+resolution is obtained than by using a smaller \fImaxzoom\fP or \fIdetail\fP\&.
 .SS Properties
 .RS
 .IP \(bu 2

version.h

@@ -1 +1 @@
-#define VERSION "tippecanoe v1.9.2\n"
+#define VERSION "tippecanoe v1.9.3\n"