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Drawing polygons with holes on map using vertices exported from QGIS?

.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty{ margin-bottom:0;
}

-1

I have exported from QGIS, for a feature in a layer, all the vertices (lat and lon) of a polygon, into a file. I'm trying now to draw that polygon using that list of vertices (that I re-read from the file), on a map on a web site but that polygon has one or more holes. So far I have been able to draw the polygon but I have issues drawing the "holes" in it. I'm working on a PoC and this is the the biggest issue met so far.

How should I handle the list of vertices from my page in order to be able to draw the polygon... and the holes as well ?

Looking at the list of vertices I can see that the initial pair of coordinate is repeated after some other vertices. This means the polygon gets closed in that point. All the other vertices coming in my list after the polygon closes, to me are holes, so as many other arrays as the holes that are in the polygon, that is so actually the first list of vertices in the list.

qgis polygon export vertices holes

share|improve this question

edited Jul 24 '18 at 21:35

PolyGeo♦

54.1k1782246

asked Jul 24 '18 at 12:35

caramelleascaramelleas

286

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Answer for Google(r) Maps: developers.google.com/maps/documentation/javascript/…
  
  – caramelleas
  Jul 24 '18 at 15:11
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Don't forget to take the Tour to learn about our focussed Q&A format.
  
  – PolyGeo♦
  Jul 24 '18 at 21:37
  

  
  
  
  

add a comment | 

-1

I have exported from QGIS, for a feature in a layer, all the vertices (lat and lon) of a polygon, into a file. I'm trying now to draw that polygon using that list of vertices (that I re-read from the file), on a map on a web site but that polygon has one or more holes. So far I have been able to draw the polygon but I have issues drawing the "holes" in it. I'm working on a PoC and this is the the biggest issue met so far.

How should I handle the list of vertices from my page in order to be able to draw the polygon... and the holes as well ?

Looking at the list of vertices I can see that the initial pair of coordinate is repeated after some other vertices. This means the polygon gets closed in that point. All the other vertices coming in my list after the polygon closes, to me are holes, so as many other arrays as the holes that are in the polygon, that is so actually the first list of vertices in the list.

qgis polygon export vertices holes

share|improve this question

edited Jul 24 '18 at 21:35

PolyGeo♦

54.1k1782246

asked Jul 24 '18 at 12:35

caramelleascaramelleas

286

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Answer for Google(r) Maps: developers.google.com/maps/documentation/javascript/…
  
  – caramelleas
  Jul 24 '18 at 15:11
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Don't forget to take the Tour to learn about our focussed Q&A format.
  
  – PolyGeo♦
  Jul 24 '18 at 21:37
  

  
  
  
  

add a comment | 

I have exported from QGIS, for a feature in a layer, all the vertices (lat and lon) of a polygon, into a file. I'm trying now to draw that polygon using that list of vertices (that I re-read from the file), on a map on a web site but that polygon has one or more holes. So far I have been able to draw the polygon but I have issues drawing the "holes" in it. I'm working on a PoC and this is the the biggest issue met so far.

How should I handle the list of vertices from my page in order to be able to draw the polygon... and the holes as well ?

Looking at the list of vertices I can see that the initial pair of coordinate is repeated after some other vertices. This means the polygon gets closed in that point. All the other vertices coming in my list after the polygon closes, to me are holes, so as many other arrays as the holes that are in the polygon, that is so actually the first list of vertices in the list.

qgis polygon export vertices holes

share|improve this question

edited Jul 24 '18 at 21:35

PolyGeo♦

54.1k1782246

asked Jul 24 '18 at 12:35

caramelleascaramelleas

286

share|improve this question

edited Jul 24 '18 at 21:35

PolyGeo♦

54.1k1782246

asked Jul 24 '18 at 12:35

caramelleascaramelleas

286

share|improve this question

edited Jul 24 '18 at 21:35

PolyGeo♦

54.1k1782246

asked Jul 24 '18 at 12:35

caramelleascaramelleas

286

edited Jul 24 '18 at 21:35

PolyGeo♦

54.1k1782246

edited Jul 24 '18 at 21:35

PolyGeo♦

54.1k1782246

asked Jul 24 '18 at 12:35

caramelleascaramelleas

286

asked Jul 24 '18 at 12:35

caramelleascaramelleas

286

1 Answer
1

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oldest

votes

1

After creating a couple of samples, I could get how the vertices list works:

Polygons are stored in a clockwise fashion except for interior polygon hole parts (i.e. 'donut holes'), which are stored in a counter-clockwise fashion. In fact, that's how polygon holes are recognized.

I did two tests following this principle: a polygon with 3 holes and a multi part poligon. In both cases this is a standard and corresponds to how vertices are returned.

As far as map polygon/holes drawing, I think there may be an API to do this, able to recognize how a list of coordinates rotates: if it is counterclockwise (= hole) or clockwise (part of a polygon).

share|improve this answer

edited 33 mins ago

PolyGeo♦

54.1k1782246

answered Jul 26 '18 at 22:55

caramelleascaramelleas

286

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  This may be of some help for the map visualization of polygons stackoverflow.com/questions/14505565/…
  
  – caramelleas
  Jul 27 '18 at 14:27
  

  
  
  
  

add a comment | 

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1

After creating a couple of samples, I could get how the vertices list works:

Polygons are stored in a clockwise fashion except for interior polygon hole parts (i.e. 'donut holes'), which are stored in a counter-clockwise fashion. In fact, that's how polygon holes are recognized.

I did two tests following this principle: a polygon with 3 holes and a multi part poligon. In both cases this is a standard and corresponds to how vertices are returned.

As far as map polygon/holes drawing, I think there may be an API to do this, able to recognize how a list of coordinates rotates: if it is counterclockwise (= hole) or clockwise (part of a polygon).

share|improve this answer

edited 33 mins ago

PolyGeo♦

54.1k1782246

answered Jul 26 '18 at 22:55

caramelleascaramelleas

286

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  This may be of some help for the map visualization of polygons stackoverflow.com/questions/14505565/…
  
  – caramelleas
  Jul 27 '18 at 14:27
  

  
  
  
  

add a comment | 

1

After creating a couple of samples, I could get how the vertices list works:

Polygons are stored in a clockwise fashion except for interior polygon hole parts (i.e. 'donut holes'), which are stored in a counter-clockwise fashion. In fact, that's how polygon holes are recognized.

I did two tests following this principle: a polygon with 3 holes and a multi part poligon. In both cases this is a standard and corresponds to how vertices are returned.

As far as map polygon/holes drawing, I think there may be an API to do this, able to recognize how a list of coordinates rotates: if it is counterclockwise (= hole) or clockwise (part of a polygon).

share|improve this answer

edited 33 mins ago

PolyGeo♦

54.1k1782246

answered Jul 26 '18 at 22:55

caramelleascaramelleas

286

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  This may be of some help for the map visualization of polygons stackoverflow.com/questions/14505565/…
  
  – caramelleas
  Jul 27 '18 at 14:27
  

  
  
  
  

add a comment | 

After creating a couple of samples, I could get how the vertices list works:

Polygons are stored in a clockwise fashion except for interior polygon hole parts (i.e. 'donut holes'), which are stored in a counter-clockwise fashion. In fact, that's how polygon holes are recognized.

I did two tests following this principle: a polygon with 3 holes and a multi part poligon. In both cases this is a standard and corresponds to how vertices are returned.

As far as map polygon/holes drawing, I think there may be an API to do this, able to recognize how a list of coordinates rotates: if it is counterclockwise (= hole) or clockwise (part of a polygon).

share|improve this answer

edited 33 mins ago

PolyGeo♦

54.1k1782246

answered Jul 26 '18 at 22:55

caramelleascaramelleas

286

share|improve this answer

edited 33 mins ago

PolyGeo♦

54.1k1782246

answered Jul 26 '18 at 22:55

caramelleascaramelleas

286

edited 33 mins ago

PolyGeo♦

54.1k1782246

edited 33 mins ago

PolyGeo♦

54.1k1782246

answered Jul 26 '18 at 22:55

caramelleascaramelleas

286

answered Jul 26 '18 at 22:55

caramelleascaramelleas

286