new D3Manager(update_rate, velocityField)
    Manages displaying everything with d3 library
    Parameters:
| Name | Type | Description | 
|---|---|---|
update_rate | 
            
            number | the update rate of the renderloop | 
velocityField | 
            
            VelocityField | the related VelocityField | 
- Source:
 
Methods
render(arrows, arrowHeads)
    renders arrows and arrowHeads
d3 update pattern explained here: http://quintonlouisaiken.com/d3-general-update-pattern/
and here: https://bost.ocks.org/mike/join/
and here is an example with lines which helped me : http://bl.ocks.org/jonsadka/482005612916b3f5e408
    Parameters:
| Name | Type | Description | 
|---|---|---|
arrows | 
            
            Array.<Arrow> | the arrows which should be rendered | 
arrowHeads | 
            
            Array.<ArrowHead> | coresponding Arrowheads | 
- Source:
 
setBackgroundImg(imgPath, width, height)
    sets the background image
    Parameters:
| Name | Type | Description | 
|---|---|---|
imgPath | 
            
            String | path to image file | 
width | 
            
            number | final image width | 
height | 
            
            height | final image height | 
- Source:
 
(inner) arrowHeadsToTriangleData(arrowHeads) → {Array}
    restructure ArrowHeads for d3
    Parameters:
| Name | Type | Description | 
|---|---|---|
arrowHeads | 
            
            Array.<ArrowHead> | the ArrowHeads | 
- Source:
 
Returns:
    restructured Arrowsheads for d3
- Type
 - Array
 
(inner) arrowsToLineData(arrows) → {Array}
    map all positional data from the arrows array to an array of coordinates for the SVG to render paths
    Parameters:
| Name | Type | Description | 
|---|---|---|
arrows | 
            
            Array.<Arrow> | the arrows | 
- Source:
 
Returns:
    restructured arrows for d3
- Type
 - Array