Map Projections (of the Earth): Any Experts?

[Qwerkey]

I am thinking of starting a project to display a revolving 3D transparent Earth globe.  To do this, I'll input a 2D map of the Earth and map that onto a sphere with _MAPTRIANGLE(3D) - I still am completely ignorant of _GL methods.

My starting problem is that I don't know which the many map projections to use to give the global Earth image the correct topology.

Would you be able to suggest what would be the most apposite project for this perceived method?  I'll probably start with Mercator if there is no guidance.

[bplus]

Happy New Year @Qwerkey,

I could fairly easily do this without GL.
1. I have code to outline the Earth's land masses on rectangular sheet
2. I have code to project a rectangular sheet onto a spinning sphere
1 + 2 = mission accomplished

In fact I had Santa & Co. silhouette orbiting the Earth one Christmas.

These are here in forum but awhile ago.

Do you need this for something else or should we leave this as exercise challenge for yourself? Or do you want this through GL (I hope Wiki GL keywords back up now?)

[Qwerkey]

Hi, @bplus Happy New Year

I'll look up your existing project (this was going to be a challenging exercise for me), but if you've covered it more-or-less I should not want to duplicate.

Richard

[MasterGy]

Hello ! I don’t want to take your mind off the creation, but I’ve done this before. For games, I use this to draw the sky. Essentially, the game is inside a sphere, so the sky is realistic.

[bplus]

Well what I thought wouldn't take much time, did. Troubles with editing the image so I could use one transparent color then troubles getting the backside working with the front side, whew! But I did it!

 

[bplus]

No sooner than I post than I get an idea for Mod!

 

Same images as in zip above, just a mod of the source code here:

Code: QB64: [Select]

1. Option _Explicit
2. _Title "Fake sphere mapping Mod 4 trans world 2" 'b+ 2022-01-02
3.  
4. Dim As Long surface, gw, gh, map, y, x
5. Dim clr~&
6. Screen _NewImage(800, 600, 32)
7. _ScreenMove 200, 100
8. surface& = _LoadImage("map.png") ' 700 x 391
9.  
10. ' new 2022-01-01 part =========================================================================
11. ' need to find the actual top, left and bottom right points inside map
12. 'Do
13. '    Cls
14. '    _PutImage (0, 0), surface&, 0
15. '    While _MouseInput: Wend
16. '    Print _MouseX, _MouseY
17. '    _Display
18. '    _Limit 100
19. 'Loop
20. ' 48 to 688 = 640 pixels  found by pointing at spots I wanted
21. ' 37 to 356 = 320 pixels
22.  
23. gw = 639
24. gh = 320
25. map& = _NewImage(gw, gh, 32)
26. '_Dest map&
27. _PutImage (0, 0)-(638, 319), surface&, map&, (48, 37)-Step(gw, gh) ' get the world section without labeling and such
28. Cls
29. _PutImage (0, 0), map&, 0 ' OK one pixel off from (48, 36)
30. For y = 0 To 319
31.     For x = 0 To 638
32.         If y = 0 Or y = 319 Then
33.             PSet (x, y), &HFF000000
34.         Else
35.             clr~& = Point(x, y)
36.             If IsNear&(clr~&, &HFFFFFFFF, 80) Then
37.                 PSet (x, y), &HFF000000
38.             Else
39.                 PSet (x, y), &HFFFFFFFF
40.             End If
41.         End If
42.     Next
43. Next
44. _PutImage (0, 0), 0, map, (0, 0)-(638, 319) ' screen to map
45. Cls
46. _PutImage (0, 0), map&, 0 ' map to screen
47. _ClearColor _RGB32(0, 0, 0), map&
48. 'Color , &HFFFFFF00    'checking
49. 'Cls
50. '_PutImage (0, 0), map&, 0 ' there is someting off white around the black lines
51. 'Sleep ' OK  got the image
52.  
53. ' ==================================================================================
54. Dim stars As Long
55.  
56. stars& = _LoadImage("stars.png")
57. _Source stars&
58. _Dest 0
59. _PutImage
60.  
61. Dim As Double r, xc, yc, xo, x1, tv, tu, xo2, rr
62. Dim pc~&
63. Dim As Long rd, gr, bl, al
64. r = _Height / 3
65. xc = _Width / 2
66. yc = _Height / 2
67. xo = 0: xo2 = .5 * gw
68. _Source map&
69. Do
70.     Cls
71.     _PutImage , stars&, 0
72.     ' new ============================= the backside!
73.     For y = -r To r
74.         x1 = Sqr(r * r - y * y)
75.         tv = (_Asin(y / r) + 1.5) / 3
76.         For x = -x1 + 1 To x1 - 1
77.             tu = (_Asin(-x / x1) + 1.5) / 6
78.             pc~& = Point((xo2 + tu * gw) Mod gw, tv * gh)
79.             cAnalysis pc~&, rd, gr, bl, al
80.             PSet (x + xc, y + yc), _RGB32(rd - 50, gr - 50, bl, al)
81.         Next
82.     Next y
83.     xo2 = (xo2 + 1) Mod gw
84.     fcirc xc, yc, r, _RGB32(255, 255, 255, 30)
85.     ' fill with some haze
86.     For rr = r To 0 Step -10
87.         fcirc xc, yc, rr, _RGB32(30, 10, 30, 40)
88.     Next
89.     '=======================================================================
90.  
91.     For y = -r To r
92.         x1 = Sqr(r * r - y * y)
93.         tv = (_Asin(y / r) + 1.5) / 3
94.         For x = -x1 + 1 To x1 - 1
95.             tu = (_Asin(x / x1) + 1.5) / 6
96.             pc~& = Point((xo + tu * gw) Mod gw, tv * gh)
97.             PSet (x + xc, y + yc), pc~&
98.         Next
99.     Next
100.     xo = (xo + 1) Mod gw
101.     _Display
102. Loop
103.  
104.  
105. Sub cAnalysis (c As _Unsigned Long, outRed As Long, outGrn As Long, outBlu As Long, outAlp As Long)
106.     outRed = _Red32(c): outGrn = _Green32(c): outBlu = _Blue32(c): outAlp = _Alpha32(c)
107.     'Print "cAnalysis says:"; outRed; outGrn; outBlu; outAlp
108. End Sub
109.  
110. 'this function needs: cAnalysis (c As _Unsigned Long, outRed as long, outGrn as long, outBlu as long, outAlp as long)
111. Function IsNear& (colr As _Unsigned Long, nearColr As _Unsigned Long, nearness As Long)
112.     'try color +-5 on RGB as near
113.     Dim As Long cRed, cGrn, cBlu, dummy, nRed, nGrn, nBlu
114.     cAnalysis colr, cRed, cGrn, cBlu, dummy
115.     'Print cRed, cGrn, cBlu
116.     cAnalysis nearColr, nRed, nGrn, nBlu, dummy
117.     'Print nRed, nGrn, nBlu
118.     If Abs(cRed - nRed) <= nearness Then
119.         If Abs(cGrn - nGrn) <= nearness Then
120.             If Abs(cBlu - nBlu) <= nearness Then IsNear& = -1
121.         End If
122.     End If
123. End Function
124.  
125. Sub fcirc (CX As Long, CY As Long, R As Long, C As _Unsigned Long)
126.     Dim Radius As Long, RadiusError As Long
127.     Dim X As Long, Y As Long
128.     Radius = Abs(R): RadiusError = -Radius: X = Radius: Y = 0
129.     If Radius = 0 Then PSet (CX, CY), C: Exit Sub
130.     Line (CX - X, CY)-(CX + X, CY), C, BF
131.     While X > Y
132.         RadiusError = RadiusError + Y * 2 + 1
133.         If RadiusError >= 0 Then
134.             If X <> Y + 1 Then
135.                 Line (CX - Y, CY - X)-(CX + Y, CY - X), C, BF
136.                 Line (CX - Y, CY + X)-(CX + Y, CY + X), C, BF
137.             End If
138.             X = X - 1
139.             RadiusError = RadiusError - X * 2
140.         End If
141.         Y = Y + 1
142.         Line (CX - X, CY - Y)-(CX + X, CY - Y), C, BF
143.         Line (CX - X, CY + Y)-(CX + X, CY + Y), C, BF
144.     Wend
145. End Sub
146.  
147.  

[johnno56]

I'm liking the background... nudge, nudge, wink, wink... lol

Cool planet!

[DANILIN]

Earth is spinning counterclockwise

Sun is first in Russia
and further Atlantic and further Alaska

[Qwerkey]

@DANILIN is quite correct.  @bplus has the World spinning in the wrong direction.

And another thing!  This was going to be my little (entertaining) project, but @bplus & @MasterGy have got there before me.  These guys don't leave any crumbs for us lower coding mortals!

However, I see that the UK doesn't appear in @bplus 's World (we're just insignificant, I know!  Along with Ireland, Iceland and other insignificant places!).  If I start my own project (where I'd had the thought of doing some _MEM manipulations as well), I might let the user choose the position of the viewing centre.  Does QB64 do "Location sensing"?

An altogether lesser mortal.

[bplus]

@DANILIN is quite correct.  @bplus has the World spinning in the wrong direction.

And another thing!  This was going to be my little (entertaining) project, but @bplus & @MasterGy have got there before me.  These guys don't leave any crumbs for us lower coding mortals!

However, I see that the UK doesn't appear in @bplus 's World (we're just insignificant, I know!  Along with Ireland, Iceland and other insignificant places!).  If I start my own project (where I'd had the thought of doing some _MEM manipulations as well), I might let the user choose the position of the viewing centre.  Does QB64 do "Location sensing"?

An altogether lesser mortal.

Right, dang! spinning is wrong and too many missing details, gots to have Ireland or I wouldn't exist :)

Maybe I'll borrow one of @MasterGy maps whose nice job also seems to have world going wrong way too plus I wouldn't mind if globe went in same direction as mouse, great focus in and out with mouse clicks!

Anyway for the technique we are using, Mercator Projection distortions on flat map seem repaired by sphere code (to answer @Qwerkey original question).

@Qwerkey mortals learn from the gods, I got my algo from Paul Dunn who is as UKanian as you. Of course it helps to have code another can read and understand mostly.

[Qwerkey]

@bplus is correct in pointing out that we mere mortals are in the presence of powers gods at QB64.  Our chief god is Germanic/Norse, Odin (or Woden in Anglo-Saxon).  He has his Special Day of the Week, of course, so perhaps we might rename this site the Wednesday Club?!

[bplus]

OK I fixed the whole world!

Got it spinning in correct direction and used MasterGy's outline-world-map.jpg which was allot easier to work with and provided much more detail.

Most all those islands are back!
 

Zip contains all you need to run and see spinning, which just needed to reverse the 2 xo ( x offset or pointer of x on map).

[MasterGy]

I think it was very good

[SierraKen]

This is INCREDIBLE B+!!! I searched for "Earth globe" and found this today. I've never seen such a good rotated Earth on my computer before. GOOD JOB!

[Pete]

Un-B-Plusing-lievable!

What is the outline-world-map.jpg used for? I see it has the country borders, but when I downloaded the "fixed" version and ran it, I still got the borderless countries display. I tried swapping out map.png with outline-world-map.jpg but no bueno.

Pete