addEdge.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
Created on Fri May 15 11:45:07 2020
@author: aransil
"""

import math

# Start and end are lists defining start and end points
# Edge x and y are lists used to construct the graph
# arrowAngle and arrowLength define properties of the arrowhead
# arrowPos is None, 'middle' or 'end' based on where on the edge you want the arrow to appear
# arrowLength is the length of the arrowhead
# arrowAngle is the angle in degrees that the arrowhead makes with the edge
# dotSize is the plotly scatter dot size you are using (used to even out line spacing when you have a mix of edge lengths)
def addEdge(start, end, edge_x, edge_y, lengthFrac=1, arrowPos = None, arrowLength=0.025, arrowAngle = 30, dotSize=40):
    
    # Get start and end cartesian coordinates
    x0, y0 = start
    x1, y1 = end
    
    # Incorporate the fraction of this segment covered by a dot into total reduction
    length = math.sqrt( (x1-x0)**2 + (y1-y0)**2 )
    dotSizeConversion = .0565/20 # length units per dot size
    convertedDotDiameter = dotSize * dotSizeConversion
    lengthFracReduction = convertedDotDiameter / length
    lengthFrac = lengthFrac - lengthFracReduction
    
    # If the line segment should not cover the entire distance, get actual start and end coords
    skipX = (x1-x0)*(1-lengthFrac)
    skipY = (y1-y0)*(1-lengthFrac)
    x0 = x0 + skipX/2
    x1 = x1 - skipX/2
    y0 = y0 + skipY/2
    y1 = y1 - skipY/2

    
    # Append line corresponding to the edge
    edge_x.append(x0)
    edge_x.append(x1)
    edge_x.append(None) # Prevents a line being drawn from end of this edge to start of next edge
    edge_y.append(y0)
    edge_y.append(y1)
    edge_y.append(None)
    
    # Draw arrow
    if not arrowPos == None:
        
        # Find the point of the arrow; assume is at end unless told middle
        pointx = x1
        pointy = y1
        
        eta = math.degrees(math.atan((x1-x0)/(y1-y0+ 0.0000001)))
        
        if arrowPos == 'middle' or arrowPos == 'mid':
            pointx = x0 + (x1-x0)/2
            pointy = y0 + (y1-y0)/2
            
        # Find the directions the arrows are pointing
        signx = (x1-x0)/abs(x1- (x0 + 0.0000001) )
        signy = (y1-y0)/abs(y1-y0 + 0.0000001)
        
        # Append first arrowhead
        dx = arrowLength * math.sin(math.radians(eta + arrowAngle))
        dy = arrowLength * math.cos(math.radians(eta + arrowAngle))    
        edge_x.append(pointx)
        edge_x.append(pointx - signx**2 * signy * dx)
        edge_x.append(None)
        edge_y.append(pointy)
        edge_y.append(pointy - signx**2 * signy * dy)
        edge_y.append(None)
        
        # And second arrowhead
        dx = arrowLength * math.sin(math.radians(eta - arrowAngle))
        dy = arrowLength * math.cos(math.radians(eta - arrowAngle))    
        edge_x.append(pointx)
        edge_x.append(pointx - signx**2 * signy * dx)
        edge_x.append(None)
        edge_y.append(pointy)
        edge_y.append(pointy - signx**2 * signy * dy)
        edge_y.append(None)
    
    
    return edge_x, edge_y