1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
|
// Robinson projection calculation
// Written by Niklas Bichinger (bichinger.de). This code is Public Domain - use as you like.
// source of robinson numbers: https://simplemaps.com/static/img/flash/robinson_projection_table.jpg
var robinsonAA = [
0.84870000,
0.84751182,
0.84479598,
0.84021300,
0.83359314,
0.82578510,
0.81475200,
0.80006949,
0.78216192,
0.76060494,
0.73658673,
0.70866450,
0.67777182,
0.64475739,
0.60987582,
0.57134484,
0.52729731,
0.48562614,
0.45167814
];
var robinsonBB = [
0.00000000,
0.08384260,
0.16768520,
0.25152780,
0.33537040,
0.41921300,
0.50305560,
0.58689820,
0.67047034,
0.75336633,
0.83518048,
0.91537187,
0.99339958,
1.06872269,
1.14066505,
1.20841528,
1.27035062,
1.31998003,
1.35230000
];
function project(latitude, longitude, mapWidth, heightFactor, mapOffsetX, mapOffsetY) {
if (typeof heightFactor === 'undefined') { heightFactor = 1; }
if (typeof mapOffsetX === 'undefined') { mapOffsetX = 0; }
if (typeof mapOffsetY === 'undefined') { mapOffsetY = 0; }
// Robinson's latitude interpolation points are in 5-degree-steps
var latitudeAbs = Math.abs(latitude);
var latitudeStepFloor = Math.floor(latitudeAbs / 5);
var latitudeStepCeil = Math.ceil(latitudeAbs / 5);
// calc interpolation factor (>=0 to <1) between two steps
var latitudeInterpolation = (latitudeAbs - latitudeStepFloor * 5) / 5;
// interpolate robinson table values
var AA = robinsonAA[latitudeStepFloor] + (robinsonAA[latitudeStepCeil] - robinsonAA[latitudeStepFloor]) * latitudeInterpolation;
var BB = robinsonBB[latitudeStepFloor] + (robinsonBB[latitudeStepCeil] - robinsonBB[latitudeStepFloor]) * latitudeInterpolation;
var robinsonWidth = 2 * Math.PI * robinsonAA[0];
var widthFactor = mapWidth / robinsonWidth;
var latitudeSign = Math.sign(latitude) || 1;
var x = (widthFactor * AA * longitude * Math.PI) / 180 + mapOffsetX;
var y = widthFactor * BB * latitudeSign * heightFactor + mapOffsetY;
return {x: x, y: y};
}
function projectAbsolute(latitude, longitude, mapWidth, heightFactor, mapOffsetX, mapOffsetY) {
if (typeof heightFactor === 'undefined') { heightFactor = 1; }
var relative = project(latitude, longitude, mapWidth, heightFactor, mapOffsetX, mapOffsetY);
var widthHeightRatio = Math.PI * robinsonAA[0] / robinsonBB[18];
var x = mapWidth / 2 + relative.x;
var y = mapWidth / widthHeightRatio * heightFactor / 2 - relative.y;
return {x: x, y: y};
}
|
