World map

[dickel]

New member here.
I have a requirement for a world map, Mercator-type projection, showing continental outlines - in the form of a 360 x 180 'dot' array to be used as an on-screen overlay for previously calculated data.  Does anyone know where I might find such an array?

Attached is an image of the general idea.

[FellippeHeitor]

I don't remember anyone doing anything similar to what you need, though. Hope something will appear.

Welcome to the forum.

[bplus]

Well if this is not homework I have something:


Oh and here's a txt file of O's and X's:

[johnno56]

Hey! What did you do with Tasmainia? (... and on a lesser note, New Zealand?)

[STxAxTIC]

Something tells me this *is* homework (without some more background elaboration on the OP's end) - and not to mention, I bet Ashish could solve this in seconds. I've seen him do similar.

[SMcNeill]

If this is a case of needing to plot points (such as for the guy who created weather maps over at [abandoned, outdated and now likely malicious qb64 dot net website - don’t go there] before it was shut down), the center looks like it should be the middle of the map, so _SCREENWIDTH \ 2, _SCREENHEIGHT \ 2 would give point 0,0....  To plot points, just calculate their distance from there. 

[dickel]

Thanks for all your replies.  Homework?  Where did that come from?  Nope, not homework!  Here's the background. 

About 25 years ago I re-wrote an existing HF radio propagation program.  The original calculated only between two fixed points — a transmitter and a receiver.  I re-wrote it to calculate from a single point (receiver) to all other points on the earth's surface at fifteen degree intervals.  (Point of interest — that version took 5 days to run on a 2Mhz Motorola MC6809 running XBASIC.)  Several years ago (when machines started to get seriously fast) I changed that to calculate at one degree intervals, i.e., a 360 x 180 map.  (I don't know how to grab a screenshot of the result but will do so when I figure it out.)

A couple of months ago I came across this site and decided to try the program again — it ran just fine and super fast too — about 5 seconds!  I never did get around to overlaying the screen plot with a world map but I am intending to do that now.

Looks to me like bplus is on the mark and I will see what I can do with his text file as that seems the best way to go.  My map is centered on 180 degrees (roughly New Zealand) so I will need to rearrange.  Thanks again.

(Yes, NZ would be a great addition (and on a lesser note, Tasmania).  Ha!  (Kiwi)

[STxAxTIC]

My bad on the homework thing - I mean, you know how this question was sounding. Can't blame us (me)! Anyway, welcome aboard.

Lemme make one question-comment... are you trying to get accurate distances on the globe using a Mercator projection? Cause... you can't right? My humble understanding of geometry (taking the earth as a sphere) dictates that you need to correct for the actual shape of the planet using a suitable coordinate system.

If you've done so, then great. If this sounds foreign, then imagine a 6 inch line in the map drawn just under the north pole. How many miles long is that? Next imagine the same-length line drawn horizontally near the equator. That one will represent way more miles.

So that's the comment. The question is: what's your distance formula?

-STx

[bplus]

Here is code, should be easy to modify if you get a map with NZ and Hawaii!

Code: QB64: [Select]

1. _TITLE "get points from map.bas for QB64 by B+ 2018-10-15"
2. CONST mw = 700 'map width
3. CONST mh = 391 ' map hieght
4. SCREEN _NEWIMAGE(700, 391, 32) 'these were map dimensions from file properties setting up a graphics screen for map
5. m& = _LOADIMAGE("map.png") 'load map
6. _PUTIMAGE , m& 'fill screen with map 1 to 1 ratio
7.  
8. 'now find corners of map inside frame borders
9. PRINT "Click top left corner."
10. getClick tlx, tly, qkeycode '                    top corner: tlx = top left x, tly = top left y
11.  
12. PRINT "Ok now click bottom right corner."
13. getClick brx, bry, qkeycode '                    bottom right corner: brx, bry
14. 'debug check our clicked points
15. 'PRINT tlx, tly, brx, bry
16.  
17. 'using corners divide distance left x and right x by 360
18. dx## = (brx - tlx) / 360
19. 'using corners divide distance bottom y to top y  by 180
20. dy## = (bry - tly) / 180
21.  
22. 'map dots array
23. DIM mp(360, 180)
24.  
25. 'for color of point x, y
26. DIM p AS _UNSIGNED LONG
27.  
28. 'fill array with point data 1 or 0 depending if line there or not
29. FOR y = 0 TO 180
30.     FOR x = 0 TO 360
31.         ding = 0 'signal a line hit in area
32.  
33.         'search around the dot for a line, otherwise too mang gaps in outlines
34.         FOR yy = -1 TO 0 'try -1 to 1, -1 to 0, or 0 to 0   to adjust number of dots on same line
35.             FOR xx = -1 TO -1 'try -1 to 1, -1 to 0, or 0 to 0  to adjust number of dots on same line
36.                 p = POINT(INT(tlx + x * dx##) + xx, INT(tly + y * dy##) + yy)
37.                 IF _RED32(p) < 100 AND _GREEN32(p) < 100 AND _BLUE32(p) < 100 THEN ding = 1: GOTO skipout
38.             NEXT
39.         NEXT
40.         skipout:
41.         IF ding THEN mp(x, y) = 1 ELSE mp(x, y) = 0
42.  
43.     NEXT
44. NEXT
45.  
46. 'draw map of dots exactly where the map.png was set
47. CLS
48. FOR y = 0 TO 180
49.     FOR x = 0 TO 360
50.         IF mp(x, y) = 1 THEN PSET (tlx + x * dx##, tly + y * dy##), _RGB32(255, 255, 255)
51.     NEXT
52. NEXT
53.  
54. 'frame the dots in a box
55. LINE (tlx, tly)-(brx, bry), _RGB32(0, 0, 200), B
56. LINE (tlx + 180 * dx##, tly)-(tlx + 180 * dx##, bry), _RGB32(0, 0, 200)
57. LINE (tlx, tly + 90 * dy##)-(brx, tly + 90 * dy##), _RGB32(0, 0, 200)
58.  
59. 'Write results to file, actually this is 361 x data points by 181 y data points
60. OPEN "360 x 180 dot array.txt" FOR OUTPUT AS #1
61. FOR y = 0 TO 180
62.     FOR x = 0 TO 360
63.         IF mp(x, y) THEN PRINT #1, "X"; ELSE PRINT #1, "O";
64.     NEXT
65.     PRINT #1, ""
66. NEXT
67. CLOSE #1
68.  
69. 'this gets mouse click location
70. SUB getClick (mx, my, q)
71.     WHILE _MOUSEINPUT: WEND ' clear previous mouse activity
72.     mx = -1: my = -1: q = 0
73.     DO WHILE mx = -1 AND my = -1
74.         q = _KEYHIT
75.         IF q = 27 OR (q > 31 AND q < 126) THEN EXIT SUB
76.         i = _MOUSEINPUT: mb = _MOUSEBUTTON(1)
77.         IF mb THEN
78.             DO WHILE mb 'wait for release
79.                 q = _KEYHIT
80.                 IF q = 27 OR (q > 31 AND q < 126) THEN EXIT SUB
81.                 i = _MOUSEINPUT: mb = _MOUSEBUTTON(1): mx = _MOUSEX: my = _MOUSEY
82.                 _LIMIT 1000
83.             LOOP
84.             EXIT SUB
85.         END IF
86.         _LIMIT 1000
87.     LOOP
88. END SUB
89.  
90.  

[dickel]

Thanks bplus.  It so happens that I DO have a map with more detail (NZ AND Tasmania!) but it also has a lot of "flyspots" on it which will require a tidy-up first.  I'll give it a shot. . .

[dickel]

My bad on the homework thing - I mean, you know how this question was sounding. Can't blame us (me)! Anyway, welcome aboard.

Lemme make one question-comment... are you trying to get accurate distances on the globe using a Mercator projection? Cause... you can't right? My humble understanding of geometry (taking the earth as a sphere) dictates that you need to correct for the actual shape of the planet using a suitable coordinate system.

If you've done so, then great. If this sounds foreign, then imagine a 6 inch line in the map drawn just under the north pole. How many miles long is that? Next imagine the same-length line drawn horizontally near the equator. That one will represent way more miles.

So that's the comment. The question is: what's your distance formula?

Thanks STx.  I don't see how "homework" came into it — must be something between the lines that I can't see — but hey, no problem at all.

No, the distances are all calculated internally for a 'spherical' earth (using high-falutin' trig functions that I couldn't possibly understand!) but the RESULTS are plotted on a 360 x 180 map — hence "Mercator" projection.

I'll see if I can find a link to the original program: "MicroMUF".

[dickel]

Screenshot was easier than I thought!

Two plots on screen:  Top represents Maximum Usable Frequency (MUF); Bottom represents Absorption Limiting Frequency (ALF).
"Maps" are centered on equator and 180 degrees with a 15-degree grid.  Legend stuff at the bottom.

A white "continental outline" overlay will be nice!

Best
Dick

[bplus]

Hi dickel,

Another way to try is transparent colors over a map background.

[dickel]

Here's the right one WITH the legend stuff — used only "Dos" available colors.

[STxAxTIC]

Beautifully retro!

I think I see what you're up to on this mission. We're all tuned in, so keep up the flow.

As for the homework thing, the red flag, so to speak, is when someone pops in out of the blue, and asks a straightforward question about... well... hm... Maybe to answer this, I defer to the supreme court's definition of pornography. I can't define it, but I know it when I see it. They were wrong about that, and so was I in this case.