Update average edge lengths (#749)

* update average edge lengths in restable docs Also added a sentence on methodology * update hard-coded avg edge length values
uber · Mar 23, 2023 · 71e09dc · 71e09dc
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diff --git a/src/h3lib/lib/latLng.c b/src/h3lib/lib/latLng.c
@@ -292,10 +292,10 @@ H3Error H3_EXPORT(getHexagonAreaAvgM2)(int res, double *out) {
 
 H3Error H3_EXPORT(getHexagonEdgeLengthAvgKm)(int res, double *out) {
     static const double lens[] = {
-        1107.712591, 418.6760055, 158.2446558, 59.81085794,
-        22.6063794,  8.544408276, 3.229482772, 1.220629759,
-        0.461354684, 0.174375668, 0.065907807, 0.024910561,
-        0.009415526, 0.003559893, 0.001348575, 0.000509713};
+        1281.256011, 483.0568391, 182.5129565, 68.97922179,
+        26.07175968, 9.854090990, 3.724532667, 1.406475763,
+        0.531414010, 0.200786148, 0.075863783, 0.028663897,
+        0.010830188, 0.004092010, 0.001546100, 0.000584169};
     if (res < 0 || res > MAX_H3_RES) {
         return E_RES_DOMAIN;
     }
@@ -305,10 +305,10 @@ H3Error H3_EXPORT(getHexagonEdgeLengthAvgKm)(int res, double *out) {
 
 H3Error H3_EXPORT(getHexagonEdgeLengthAvgM)(int res, double *out) {
     static const double lens[] = {
-        1107712.591, 418676.0055, 158244.6558, 59810.85794,
-        22606.3794,  8544.408276, 3229.482772, 1220.629759,
-        461.3546837, 174.3756681, 65.90780749, 24.9105614,
-        9.415526211, 3.559893033, 1.348574562, 0.509713273};
+        1281256.011, 483056.8391, 182512.9565, 68979.22179,
+        26071.75968, 9854.090990, 3724.532667, 1406.475763,
+        531.4140101, 200.7861476, 75.86378287, 28.66389748,
+        10.83018784, 4.092010473, 1.546099657, 0.584168630};
     if (res < 0 || res > MAX_H3_RES) {
         return E_RES_DOMAIN;
     }

diff --git a/website/docs/library/restable.md b/website/docs/library/restable.md
@@ -131,32 +131,28 @@ Edge lengths are computed with a **spherical** model of the earth using the
 [authalic radius](https://en.wikipedia.org/wiki/Earth_radius#Authalic_radius)
 given by
 [WGS84](https://en.wikipedia.org/wiki/WGS84)/[EPSG:4326](https://epsg.io/4326).
-:::
-
-:::danger
-These values are hard coded into the `getHexagonEdgeLengthAvgKm` function and
-related functions in the H3 library. There are [known issues](https://github.com/uber/h3/issues/666)
-with these numbers and they are expected to be updated later.
+Average edge lengths were calculated exactly for resolutions 0 through 6 and 
+extrapolated for finer resolutions.
 :::
 
 | Res | Average edge length (Km) |
 |----:|-------------------------:|
-|   0 | 1107.712591              |
-|   1 | 418.6760055              |
-|   2 | 158.2446558              |
-|   3 | 59.81085794              |
-|   4 | 22.6063794               |
-|   5 | 8.544408276              |
-|   6 | 3.229482772              |
-|   7 | 1.220629759              |
-|   8 | 0.461354684              |
-|   9 | 0.174375668              |
-|  10 | 0.065907807              |
-|  11 | 0.024910561              |
-|  12 | 0.009415526              |
-|  13 | 0.003559893              |
-|  14 | 0.001348575              |
-|  15 | 0.000509713              |
+|   0 | 1281.256011              |
+|   1 | 483.0568391              |
+|   2 | 182.5129565              |
+|   3 | 68.97922179              |
+|   4 | 26.07175968              |
+|   5 | 9.854090990              |
+|   6 | 3.724532667              |
+|   7 | 1.406475763              |
+|   8 | 0.531414010              |
+|   9 | 0.200786148              |
+|  10 | 0.075863783              |
+|  11 | 0.028663897              |
+|  12 | 0.010830188              |
+|  13 | 0.004092010              |
+|  14 | 0.001546100              |
+|  15 | 0.000584169              |
 
 ## Appendix: Methodology