1

Following this question,

D3.geo : Spherical arcs rather than straight lines for parallels?

I was able to draw projected polygons (1) by using path:

var poligono = {                                                                                                                      
"type": "Polygon",                                                                                                                
"coordinates": [                                                                   
    [[0, 0], [0, 20], [100, 20], [100, 0], [0, 0]]                                                              
  ]
}

 // [...]                                                                                                                                     

   svg.append("path")                                                                                                                  
  .attr("class", "arc")                                                                                                               
  .attr("d", path(poligono));                                                                                                         

and unprojected rectangles (2) using .outline():

  var arc = d3.geoGraticule()                                                                                                         
 .extentMajor([[0, 0], [-20, -20]])          

     // [...]                                                                                                                                     


  svg.append("path")                                                                                                                  
  .attr("class", "arc")                                                                                                               
  .attr("d", path(arc.outline()));                                                                                                    

What is the best way to draw a polygon such as the blue one in the figure (3), i.e. an unprojected polygon enrolling the cylinder for more than 360°?

unprojecgted example

(The general goal is to draw this kind of surfaces on a generic cylinder, and not specifically on a geographic projection)

Roy Scheffers
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leonard vertighel
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