| Bug in mapped polygon objects? [message #91905] |
Mon, 14 September 2015 18:52  |
penteado
Messages: 866
Registered: February 2018
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Senior Member
Administrator |
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Hello,
While developing a mapping application, I found what seems to be an odd bug with fill colors for polygon objects on maps. This happens both on imaps and on Function Graphics maps - due to both of them using ipolygon. The problem only happens on some polygons, apparently due to the way they are tessellated when placed on a map projection.
This shows an example where things work as expected:
lats2=[55d0,55d0,-45d0,-45d0,35d0,35d0,-15d0,-15d0]
lons2=[15d0,65d0,75d0,25d0,-15d0,-35d0,-35d0,-15d0]
colors2=[[255,0,0],[255,0,0],[255,0,0],[255,0,0],$
[0,0,255],[0,0,255],[0,0,255],[0,0,255]]
conn2=[4,0,1,2,3,4,4,5,6,7]
imap,map_projection='equirectangular',background='cyan'
ipolygon,transpose([[lons2],[lats2]]),vert_colors=colors2,$
connectivity=conn2,/data,/visualization
However, with some polygons (in this case, straddling the 0 longitude line), the problem shows up:
lats=[55d0,55d0,-45d0,-45d0,35d0,35d0,-15d0,-15d0]
lons=[-15d0,65d0,75d0,-25d0,-15d0,-35d0,-35d0,-15d0]
colors=[[255,0,0],[255,0,0],[255,0,0],[255,0,0],$
[0,0,255],[0,0,255],[0,0,255],[0,0,255]]
conn=[4,0,1,2,3,4,4,5,6,7]
imap,map_projection='equirectangular',background='cyan'
ipolygon,transpose([[lons],[lats]]),vert_colors=colors,$
connectivity=conn,/data,/visualization
The polygons are drawn with a white fill color, instead of the specified colors.
I tracked this down to the IDLitVisPolygon::_TessellateShapes method, which at lines 540-544 (in the IDL 8.5 version) resets the colors to zero when the tessellation changes the number of vertices, causing a mismatch with the number of colors.
To get around this and make my application work, I copied the source code of that method into my own file, where I edited those 5 lines of code. My programs then compile this edited version of that method before they try to draw the polygons. If anyone is interested in seeing the edit, it is lines 117-120 of http://www.ppenteado.net/idl/pp_lib/doc/tessellateshapes_pp. html
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| Re: Bug in mapped polygon objects? [message #91930 is a reply to message #91905] |
Wed, 16 September 2015 09:15  |
chris_torrence@NOSPAM
Messages: 528
Registered: March 2007
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Senior Member |
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On Monday, September 14, 2015 at 7:52:51 PM UTC-6, Paulo Penteado wrote:
> Hello,
>
> While developing a mapping application, I found what seems to be an odd bug with fill colors for polygon objects on maps. This happens both on imaps and on Function Graphics maps - due to both of them using ipolygon. The problem only happens on some polygons, apparently due to the way they are tessellated when placed on a map projection.
>
> This shows an example where things work as expected:
>
> lats2=[55d0,55d0,-45d0,-45d0,35d0,35d0,-15d0,-15d0]
> lons2=[15d0,65d0,75d0,25d0,-15d0,-35d0,-35d0,-15d0]
> colors2=[[255,0,0],[255,0,0],[255,0,0],[255,0,0],$
> [0,0,255],[0,0,255],[0,0,255],[0,0,255]]
> conn2=[4,0,1,2,3,4,4,5,6,7]
>
> imap,map_projection='equirectangular',background='cyan'
> ipolygon,transpose([[lons2],[lats2]]),vert_colors=colors2,$
> connectivity=conn2,/data,/visualization
>
> However, with some polygons (in this case, straddling the 0 longitude line), the problem shows up:
>
> lats=[55d0,55d0,-45d0,-45d0,35d0,35d0,-15d0,-15d0]
> lons=[-15d0,65d0,75d0,-25d0,-15d0,-35d0,-35d0,-15d0]
> colors=[[255,0,0],[255,0,0],[255,0,0],[255,0,0],$
> [0,0,255],[0,0,255],[0,0,255],[0,0,255]]
> conn=[4,0,1,2,3,4,4,5,6,7]
>
> imap,map_projection='equirectangular',background='cyan'
> ipolygon,transpose([[lons],[lats]]),vert_colors=colors,$
> connectivity=conn,/data,/visualization
>
> The polygons are drawn with a white fill color, instead of the specified colors.
>
> I tracked this down to the IDLitVisPolygon::_TessellateShapes method, which at lines 540-544 (in the IDL 8.5 version) resets the colors to zero when the tessellation changes the number of vertices, causing a mismatch with the number of colors.
>
> To get around this and make my application work, I copied the source code of that method into my own file, where I edited those 5 lines of code. My programs then compile this edited version of that method before they try to draw the polygons. If anyone is interested in seeing the edit, it is lines 117-120 of http://www.ppenteado.net/idl/pp_lib/doc/tessellateshapes_pp. html
Thanks Paulo,
I just incorporated a slightly-different version of your fix into the IDL code.
Cheers,
Chris
p.s. here's my code block:
if (nsubvert lt nsubcolor) then begin
; If we have fewer vertices, just keep the first nsubvert colors.
color1 = color1[*,0:nsubvert-1]
endif else if (nsubvert gt nsubcolor) then begin
; If we have more vertices, just repeat the colors.
index = LINDGEN(nsubvert) mod nsubcolor
color1 = color1[*,index]
endif
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| Re: Bug in mapped polygon objects? [message #91939 is a reply to message #91930] |
Mon, 21 September 2015 14:37 |
penteado
Messages: 866
Registered: February 2018
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Senior Member
Administrator |
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Thanks, Chris! That fix does look better than what I wrote. When the next IDl release is out with that fix, I will add a test in my code, so that my fix only gets compiled if the IDL version is 8.5 or lower.
On Wednesday, September 16, 2015 at 9:15:09 AM UTC-7, Chris Torrence wrote:
> Thanks Paulo,
> I just incorporated a slightly-different version of your fix into the IDL code.
> Cheers,
> Chris
> p.s. here's my code block:
>
> if (nsubvert lt nsubcolor) then begin
> ; If we have fewer vertices, just keep the first nsubvert colors.
> color1 = color1[*,0:nsubvert-1]
> endif else if (nsubvert gt nsubcolor) then begin
> ; If we have more vertices, just repeat the colors.
> index = LINDGEN(nsubvert) mod nsubcolor
> color1 = color1[*,index]
> endif
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