render_example_test.gno

 1package geohashdemo
 2
 3// ExampleRender pins the realm's root Render output as a testable example.
 4func ExampleRender() {
 5	print(Render(""))
 6	// Output:
 7	// # Geohash
 8	//
 9	// Turning a latitude and longitude into a short base32 string, demoing the [`p/moul/x/daily/geohash`](/p/moul/x/daily/geohash/v0) library.
10	//
11	// ## One point, at growing precision
12	//
13	// Jutland, Denmark, at 57.64911, 10.40744:
14	//
15	// ```
16	//  1  u
17	//  2  u4
18	//  3  u4p
19	//  4  u4pr
20	//  5  u4pru
21	//  6  u4pruy
22	//  7  u4pruyd
23	//  8  u4pruydq
24	//  9  u4pruydqq
25	// 10  u4pruydqqv
26	// 11  u4pruydqqvj
27	// ```
28	//
29	// Every character adds five bits and every prefix is itself a valid geohash of the same place, so truncating one zooms out. Two hashes sharing a long prefix are close together, which is what lets an avl tree keyed this way answer "everything near here" with a range scan and no geometry at all.
30	//
31	// Two more places, at the length each one needs:
32	//
33	// - Null Island (0, 0): `s0000`
34	// - Leon, Spain (42.6, -5.6): `ezs42`
35	// - Jutland, Denmark (57.64911, 10.40744): `u4pruy`
36	//
37	// > Next: [`/cell`](/r/moul/x/daily/geohashdemo/v0:cell) for the box a hash names, [`/neighbors`](/r/moul/x/daily/geohashdemo/v0:neighbors) for the eight cells around one.
38}
39
40// ExampleRender_cell pins the page that shows a geohash is a box, not a point.
41func ExampleRender_cell() {
42	print(Render("/cell"))
43	// Output:
44	// # Geohash
45	//
46	// Turning a latitude and longitude into a short base32 string, demoing the [`p/moul/x/daily/geohash`](/p/moul/x/daily/geohash/v0) library.
47	//
48	// ## The box `ezs42` names
49	//
50	// A geohash is a box, never a point, and the shorter the hash the bigger the box.
51	//
52	// ```
53	// latitude   42.5830078125 .. 42.626953125
54	// longitude  -5.625 .. -5.5810546875
55	// size       0.0439453125 by 0.0439453125 degrees
56	// ```
57	//
58	// `Decode` reports the centre, 42.60498046875, -5.60302734375, because the centre is the best single point a box can give. The coordinates that produced the hash, 42.6, -5.6, are inside it: yes.
59	//
60	// Null Island is not: no.
61	//
62	// > Next: [`/neighbors`](/r/moul/x/daily/geohashdemo/v0:neighbors).
63}
64
65// ExampleRender_neighbors pins the eight surrounding cells and the wrap at the
66// antimeridian.
67func ExampleRender_neighbors() {
68	print(Render("/neighbors"))
69	// Output:
70	// # Geohash
71	//
72	// Turning a latitude and longitude into a short base32 string, demoing the [`p/moul/x/daily/geohash`](/p/moul/x/daily/geohash/v0) library.
73	//
74	// ## The eight cells around `ezs42`
75	//
76	// ```
77	// ezefx ezs48 ezs49
78	// ezefr ezs42 ezs43
79	// ezefp ezs40 ezs41
80	// ```
81	//
82	// Each one is computed by walking exactly one cell from the centre and re-encoding. Every bound is an exact binary fraction, so the step lands on another centre rather than near one, and stepping back is the identity.
83	//
84	// ### The antimeridian is not an edge of the world
85	//
86	// `z` is the top right corner cell of the world. The cell east of it is `b`, the top left one, because longitude wraps. The classic lookup-table implementations report nothing there, which is a property of the tables and not of the globe.
87	//
88	// Latitude genuinely stops, though, so `z` has no northern neighbour and `Neighbors` returns 5 cells rather than eight: `b`, `8`, `x`, `w`, `y`.
89	//
90	// > Back to [the overview](/r/moul/x/daily/geohashdemo/v0).
91}