Add an option to generate label points in place of polygons (#20)

* Add an option to generate label points in place of polygons

* Change all these places where I said "extent" but really meant "area"

* Revert "Change all these places where I said "extent" but really meant "area""

This reverts commit 403828d.

* Add --order-smallest-first and --order-largest-first options

* Use Turf's center-of-mass algorithm for polygon label points

* If the label point isn't within the polygon, find one that is

* Don't choose a label point that is too close to a border

* Try a little harder to find an optimal label point

* Checkerboard which tiles labels are generated in, to reduce adjacency

* Use a label point for the general representative point for polygons

(Skipping the iteration to find one that is as far as possible from
the borders)

This makes the labels look better in many cases (like France at z1)
but unfortunately ripples into changing the sequence of polygons in
many tests, so the diff is big.

* Revert "Use a label point for the general representative point for polygons"

This reverts commit 2261adf.

* Checkpoint work on spiral labels

* Clip label spirals to the feature bounds

* Fix label test

* Be careful not to place spiral labels too close to borders either

* For spiral anchors, only check tile scale, not feature size

* Update test

* Only try to find a central label point for the largest ring

* In tiny polygon dust, keep the attributes of the largest feature

CHANGELOG.md

@@ -1,3 +1,9 @@
+## 2.9.0
+
+* Add an option to generate label points in place of polygons
+* Add --order-smallest-first and --order-largest-first options
+* When tiny polygons are being aggregated into dust, keep the attributes of the largest.
+
 ## 2.8.1
 
 * Improve precision of polygon ring area calculations

README.md

@@ -506,6 +506,8 @@ the same layer, enclose them in an `all` expression so they will all be evaluate
  * `-ah` or `--hilbert`: Put features in Hilbert Curve order instead of the usual Z-Order. This improves the odds that spatially adjacent features will be sequentially adjacent, and should improve density calculations and spatial coalescing. It should be the default eventually.
  * `--order-by=`_attribute_: Order features by the specified _attribute_, in alphabetical or numerical order. Multiple `--order-by` and `--order-descending-by` options may be specified, the first being the primary sort key.
  * `--order-descending-by=`_attribute_: Order features by the specified _attribute_, in reverse alphabetical or numerical order. Multiple `--order-by` and `--order-descending-by` options may be specified, the first being the primary sort key.
+ * `--order-smallest-first`: Order features so the smallest geometry comes first in each tile. Multiple `--order-by` and `--order-descending-by` options may be specified, the first being the primary sort key.
+ * `--order-largest-first`: Order features so the largest geometry comes first in each tile. Multiple `--order-by` and `--order-descending-by` options may be specified, the first being the primary sort key.
 
 ### Adding calculated attributes
 
@@ -518,6 +520,7 @@ the same layer, enclose them in an `all` expression so they will all be evaluate
  * `-pw` or `--use-source-polygon-winding`: Instead of respecting GeoJSON polygon ring order, use the original polygon winding in the source data to distinguish inner (clockwise) and outer (counterclockwise) polygon rings.
  * `-pW` or `--reverse-source-polygon-winding`: Instead of respecting GeoJSON polygon ring order, use the opposite of the original polygon winding in the source data to distinguish inner (counterclockwise) and outer (clockwise) polygon rings.
  * `--clip-bounding-box=`*minlon*`,`*minlat*`,`*maxlon*`,`*maxlat*: Clip all features to the specified bounding box.
+ * `-aP` or `--convert-polygons-to-label-points`: Replace polygon geometries with a label point or points for the polygon in each tile it intersects.
 
 ### Setting or disabling tile size limits
 

errors.hpp

@@ -19,3 +19,5 @@
 #define EXIT_UNLINK 118
 #define EXIT_UTF8 119
 #define EXIT_WRITE 120
+
+// avoid 124, 125, 126, 127, 137, which are used by GNU timeout