topic Re: Creating Polylines to track migration in Geoprocessing Questions

Creating Polylines to track migration

RichardOwens1 — Fri, 23 Jan 2015 07:21:15 GMT

Hello!

I am a beginner in GIS and would like to create a representation of migration across borders. Can anyone recommend a "how to" resource?

I would like to show the movement from provinces, districts and/or towns.

Re: Creating Polylines to track migration

XanderBakker — Fri, 23 Jan 2015 13:01:11 GMT

If you have a table with the X,Y (or lat, lon) of the from and to locations on a single record you can use the XY To Line (Data Management) tool. This will create straight lines between the from and to locations. The bad thing about this is that if you have migration between two locations in both directions, it will overlap.

Re: Creating Polylines to track migration

XanderBakker — Sun, 12 Dec 2021 08:19:23 GMT

In case you don't want to have straight lines you could do something like this (black lines are the curves created in the script):

... using a little of Python code (ugly, I know, but will clean it up and convert it into a toolbox later...)

import arcpy
import math

def main():
    tbl = r"D:\Xander\GeoNet\MigrationRoutes\gdb\test.gdb\test_tbl"
    fc_out = r"D:\Xander\GeoNet\MigrationRoutes\gdb\test.gdb\migration06"
    sr = arcpy.SpatialReference(28992)

    flds = ("X1", "Y1", "X2", "Y2")
    curvature = 0.05 # 5%
    pnts_on_curve = 100

    lst_lines = []
    with arcpy.da.SearchCursor(tbl, flds) as curs:
        for row in curs:
            pnt1 = arcpy.Point(row[0], row[1])
            pnt2 = arcpy.Point(row[2], row[3])
            line = arcpy.Polyline(arcpy.Array([pnt1, pnt2]), sr)
            length = line.length
            offset = curvature * length
            delta_x = row[2] - row[0]
            delta_y = row[3] - row[1]

            # extract points on line
            arr = arcpy.Array()
            for i in range(0, pnts_on_curve + 1):
                frac = i / float(pnts_on_curve)
                pnt = line.positionAlongLine(frac, use_percentage=True)
                line_perp = perpendicular_line(line.firstPoint, line.lastPoint, pnt.firstPoint)
                asin = math.sin(frac * math.pi)
                dist_off = offset * asin
                pnt_new = line_perp.positionAlongLine(dist_off, use_percentage=False)
                arr.add(pnt_new.firstPoint)
            line_new = arcpy.Polyline(arr, sr)
            lst_lines.append(line_new)

    arcpy.CopyFeatures_management(lst_lines, fc_out)


class Coord(object):
    def __init__(self,x,y):
        self.x = x
        self.y = y

    def __sub__(self,other):
        # This allows you to substract vectors
        return Coord(self.x-other.x,self.y-other.y)

    def __repr__(self):
        # Used to get human readable coordinates when printing
        return "Coord(%f,%f)"%(self.x,self.y)

    def length(self):
        # Returns the length of the vector
        return math.sqrt(self.x**2 + self.y**2)

    def angle(self):
        # Returns the vector's angle
        return math.atan2(self.y,self.x)

def normalize(coord):
    return Coord(
        coord.x/coord.length(),
        coord.y/coord.length()
        )

def perpendicular(coord):
    return Coord(
        coord.length()*math.cos(coord.angle()+math.pi/2),
        coord.length()*math.sin(coord.angle()+math.pi/2)
        )

def perpendicular_line(coord_from, coord_to, coord_at):
    length = math.hypot(coord_from.X - coord_to.X, coord_from.Y - coord_to.Y)
    a = Coord(coord_from.X, coord_from.Y)
    b = Coord(coord_to.X, coord_to.Y)
    perp = perpendicular(normalize(a-b))
    perp_len = Coord(perp.x*length, perp.y*length)
    coord_perp = Coord(perp_len.x+coord_at.X, perp_len.y+coord_at.Y)
    return arcpy.Polyline(arcpy.Array([coord_at,
                                      arcpy.Point(coord_perp.x, coord_perp.y)]))


if __name__ == '__main__':
    main()

Re: Creating Polylines to track migration

XanderBakker — Fri, 23 Jan 2015 21:36:09 GMT

Find attached the toolbox. In case of any problems, please post them back. The toolbox was created with ArcGIS 10.3.

Re: Creating Polylines to track migration

SteveCline — Sat, 24 Jan 2015 03:50:55 GMT

Thank you for the tool. This looks like what I need. I will give it a try and let you know.

Re: Creating Polylines to track migration

RichardOwens1 — Sun, 25 Jan 2015 08:09:33 GMT

Thank you for this information. I will make x,y tables and see if I can get this to work. I am using arcmap 10.1, and I have not used Python yet. Now I will take a class in how to apply it.

-Rich

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