Add sample lat-lon data

docs/DESIGN.adoc

@@ -744,6 +744,24 @@ fn st_to_ij(s: f64) -> u32 {
 }
 ----
 
+== Sample Data [[sample-data]]
+
+In order to test this algorithm out, I want to ensure the conversions are not incorrect.
+I will generate sample data and test against the link:https://github.com/google/s2geometry/[S2 C++ Source Code^] to ensure the CellIDs match for every tested latitude longitude.
+
+.Types of test data
+
+* Standard latitude/longitude in the range (-90,90) and (-180,180) - Randomly selected
+* Non-normalized latitude/longitude in the range [-1000,1000] and [-1000,1000] - Used to make sure latitude/longitude normalization logic is correct
+* Corner-cases - 0, ±1, ±90, and ±180, plus some variation
+
+All of these cases are generated with this code:
+
+[source,python]
+----
+include::./generate-test-data.py[]
+----
+
 == Interfaces [[interfaces]]
 
 Goal 2 of this project is to provide many interfaces that are easy to use.

docs/generate-test-data.py

@@ -0,0 +1,27 @@
+from random import random
+with open("sample-lat-lon.csv", "w") as f:
+    f.write("lat,lon\n")
+
+    # Edge cases
+    # Do both positive and negative
+    for neg in ("-", ""):
+        # Add a little bit of variation
+        for dec in ("0", "00000001", "5", "05", "9999"):
+            # Possibly strange latitudes
+            for lat_i in (0, 1, 90):
+                # Possibly strong longitudes
+                for lon_i in (0, 1, 90, 180):
+                    f.write(f"{neg}{lat_i}.{dec},")
+                    f.write(f"{neg}{lon_i}.{dec}\n")
+
+    # Normalized
+    for i in range(10000):
+        lat = (random() - .5) * 2 * 90
+        lon = (random() - .5) * 2 * 180
+        f.write(f"{lat},{lon}\n")
+
+    # Non-normalized
+    for i in range(10000):
+        lat = (random() - .5) * 2 * 1000
+        lon = (random() - .5) * 2 * 1000
+        f.write(f"{lat},{lon}\n")