topic Re: Distance between points along a polyline in Spatial Data Science Questions

Distance between points along a polyline

JodyCamille — Sun, 01 Feb 2015 13:36:41 GMT

I have points marking tagged fish locations along a river. How do I measure the distance between each of those successive points?

Re: Distance between points along a polyline

DanPatterson_Retired — Sat, 11 Dec 2021 06:30:46 GMT

You don't specify the format of your data...but lets assume that the points are in sequential order in something like a shapefile's table. You can create a new field in your table (ie Dist type double etc) and use one of the code blocks specifying a Python parser and copying

dist_between(!Shape!) or dist_cumu(!Shape!)

depending upon whether you need inter-point distance or cumulative distance. (Note...haven't tested in a long time)

EDIT this will give you the point to point distance, if you points form part of the polyline, convert the polyline to points first

otherwise you will get the Euclidean distance between the points and not the points along the polyline

for interpoint distance

I have added a function to produce points along a polyline based upon an increment if that will help

''' input shape field: returns distance between points
dist_between(!Shape!)    #enter into the expression box'''
x0 = 0.0;  y0 = 0.0;  distance = 0.0
def dist_between(shape):
  global x0;  global y0;  global distance
  x = shape.firstpoint.X;  y = shape.firstpoint.Y
  if x0 == 0.0 and y0 == 0.0:
    x0 = x; y0 = y
  distance = math.sqrt((x - x0)**2 + (y - y0)**2)
  x0 = x;  y0 = y
  return distance

for cumulative distance

''' input shape field: returns cumulative distance between points
dist_cumu(!Shape!)    #enter into the expression box'''
x0 = 0.0;  y0 = 0.0;  distance = 0.0
def dist_cumu(shape):
  global x0;  global y0;  global distance
  x = shape.firstpoint.X;  y = shape.firstpoint.Y
  if x0 == 0.0 and y0 == 0.0:
    x0 = x; y0 = y
  distance += math.sqrt((x - x0)**2 + (y - y0)**2)
  x0 = x;  y0 = y
  return distance

# create points along polyline example
''' input shape field, value (distance or decimal fraction, 0-1), use_fraction (True/False), XorY (X or Y):
    returns a point x meters or x  decimal fraction along a line, user specifies whether X or Y coordinates
pnt_along(!Shape!, 100, False, 'X')    #eg.  calculate X coordinate 100 m from start point '''
def pnt_along(shape, value, use_fraction, XorY):
  XorY = XorY.upper()
  if use_fraction and (value > 1.0):
    value = value/100.0
  if shape.type == "polygon":
    shape = shape.boundary()
  pnt = shape.positionAlongLine(value,use_fraction)
  if XorY == 'X':  return pnt.centroid.X
  else:  return pnt.centroid.Y

Re: Distance between points along a polyline

MohamedMagdy — Sun, 01 Feb 2015 15:08:21 GMT

If these points located along river line you can use linear referenceing tool to measure the route length along river

ArcGIS Help 10.1

Re: Distance between points along a polyline

XanderBakker — Sat, 11 Dec 2021 06:30:48 GMT

In case you have a featureclass with the river (1 line) and a point featureclass with the fishing locations, then you should snap those points to the line, obtain the position of the snapped points on the line, define the distance from the start of the river, sort the location on distance from start and determine the distance between consecutive points. In python this would look like this:

import arcpy

fc_pnt = r"C:\Forum\Fishing\test.gdb\fishingpoints"
fc_line = r"C:\Forum\Fishing\test.gdb\river"
fld_diststart = "DistStart"
fld_distprevious = "DistPrev"

# add fields to point featureclass in case they do not exist
add_flds = [fld_diststart, fld_distprevious]
for fld in add_flds:
    if len(arcpy.ListFields(fc_pnt, wild_card=fld)) == 0:
        arcpy.AddField_management(fc_pnt, fld, "DOUBLE")

# get first (only?) polyline from lines featureclass
polyline = arcpy.da.SearchCursor(fc_line, ("SHAPE@",)).next()[0]

dct = {}
flds = ("SHAPE@", "OID@", fld_diststart)
with arcpy.da.SearchCursor(fc_pnt, flds) as curs:
    for row in curs:
        pnt = row[0]
        oid = row[1]
        diststart = polyline.queryPointAndDistance(pnt, False)
        dct[oid] = diststart[1]
del curs, row

# sort on distance and determine distance between points
dct2 = {}
cnt = 0
for oid, diststart in sorted(dct.items(), key=lambda x: x[1]):
    cnt += 1
    if cnt == 1:
        distbetween = 0
        distprev = diststart
    else:
        distbetween = diststart - distprev
        distprev = diststart
    dct2[oid] = distbetween

# update the points fc
flds = ("OID@", fld_diststart, fld_distprevious)
with arcpy.da.UpdateCursor(fc_pnt, flds) as curs:
    for row in curs:
        oid = row[0]
        row[1] = dct[oid]
        row[2] = dct2[oid]
        curs.updateRow(row)
del curs, row

The result will look like this:

Re: Distance between points along a polyline

MohammedAlhessi2 — Sun, 01 Feb 2015 16:45:33 GMT

you have many choices. Using the linear referencing as Mohammed Magdy mentioned gives you the cumulative distance from the start of the river. There is another method which utilizes the "Point Distance Tool". The output of the tool is a table containing all distances from any point to other points. For example, If you have 8 points, then the distances from the point 1 to the other seven points are computed and then the distances from point 2 to the other seven points are computed and stored and so on.

There is another method which could be useful. you can split the river into segments at the fishing sites using "Split Line At Point" tool and store the output in a feature class inside a geodatabase. then you can find the distances stored in the Shape_Length field of the output feature class.

Re: Distance between points along a polyline

JodyCamille — Fri, 06 Feb 2015 19:35:45 GMT

I appreciate your comments, Dan.

I have a point shapefile of tagged fish locations. I snapped those points to a polyline shapefile of the rivers that the fish migrated on. Should I convert the river (polyline) shapefile to a point file and calculate your code on a distance field in that newly converted point file?

Thank you,

Jody

Re: Distance between points along a polyline

XanderBakker — Fri, 06 Feb 2015 19:46:44 GMT

Did you try the code I posted? It does not require you to snap your points to the river...

Re: Distance between points along a polyline

DanPatterson_Retired — Fri, 06 Feb 2015 22:07:43 GMT

No...as indicated, the interpoint distance examples I suggested would give you the Euclidean distance between the points, I think you want points to be along the polyline after they are snapped, then distance determined along the polyline...I would go with Xander's solution...just change the input files and run his script in a script editor

Re: Distance between points along a polyline

KelseyRydland — Thu, 28 May 2015 17:51:21 GMT

If you have the Network Analyst extension I think you might find that it is easiest to use the Origins Destinations (OD) Cost Matrix tool. I have done this for several instances like this and it works well. You do need to create a network dataset using fish locations as point data and then your stream(s) as your line data. ESRI has a nice overview of the tool here:

http://resources.arcgis.com/en/help/main/10.1/index.html#//00480000000m000000

Re: Distance between points along a polyline

KirstenLawrence — Sat, 01 Aug 2015 19:09:26 GMT

This looks like a good script for my needs right now. I have many points that are associated with many different lines. They don't necessarily fall on the lines but I know which line they should be associated with by a unique line ID. It seems I can use your script above but I need to somehow find the right line for the right points. Seems like maybe I should set up a cursor first for the lines that accesses the unique line ID field, and below set up a cursor for the points that accesses the unique line ID field that is attached to the points, and when those values match, then do the distance calculations? The data is multidimensional, where I have groups of points associated with a vehicle, and there are time values for each point as well, that essentially represent trips along each line. I've already sorted on the vehicle ID, the line ID, the time and the coords and now want to calculate the distance, and ultimately the speed of the vehicle between each point.

Re: Distance between points along a polyline

RichardFairhurst — Sat, 11 Dec 2021 06:30:51 GMT

Your are wrong on how you should approach this problem. Embedded cursors are virtually never the solution to any problem. Use a dictionary to make the match between the line IDs and the points and then process one cursor normally. The larger your datasets get the embedded cursors slow down exponentially, while Dictionaries have a linear performance impact. So for 10000 points on 100 lines embedded cursors will perform at least 100 times slower than a dictionary lookup.

Although I have not tested the code below, I believe it will work. The main part I am unsure of is the sort of dct that creates dct2. In any case, once all bugs are worked out this code will perform wonderfully.

import arcpy  
  
fc_pnt = r"C:\Forum\Fishing\test.gdb\fishingpoints"  
fc_line = r"C:\Forum\Fishing\test.gdb\river"  
fld_diststart = "DistStart"  
fld_distprevious = "DistPrev"  
  
# add fields to point featureclass in case they do not exist  
add_flds = [fld_diststart, fld_distprevious]  
for fld in add_flds:  
    if len(arcpy.ListFields(fc_pnt, wild_card=fld)) == 0:  
        arcpy.AddField_management(fc_pnt, fld, "DOUBLE")  

fields = ["LINE_ID", "SHAPE@"]

# Create a dictionary of lines with their geometry
valueDict = {r[0]:(r[1:]) for r in arcpy.da.SearchCursor(fc_line, fields)}
  
dct = {}  
flds = ["LINE_ID", "SHAPE@", "OID@", fld_diststart]
with arcpy.da.SearchCursor(fc_pnt, flds) as curs:  
    for row in curs:
        line = row[0]
        if line in valueDict:
            polyline = valueDict[line]
            pnt = row[1]  
            oid = row[2]  
            diststart = polyline.queryPointAndDistance(pnt, False)  
            dct[(line, oid)] = diststart[1]
del curs, row  

# sort on distance and determine distance between points  
dct2 = {}  
cnt = 0
prevline = -1  
for line_oid, diststart in sorted(dct.items(), key=lambda x: x[1]):  
    cnt += 1  
    if cnt == 1:  
        distbetween = 0  
        distprev = diststart
        prevline = line_oid[0] 
    elif line_oid[0] != prevline: 
        distbetween = 0  
        distprev = diststart
        prevline = line_oid[0] 
    else:  
        distbetween = diststart - distprev  
        distprev = diststart  
    dct2[line_oid] = distbetween  
  
# update the points fc  
flds = ("LINE_ID", "OID@", fld_diststart, fld_distprevious)  
with arcpy.da.UpdateCursor(fc_pnt, flds) as curs:  
    for row in curs:  
        line = row[0]
        oid = row[1]  
        if (line, oid) in dct:
            row[2] = dct[(line, oid)]  
            row[3] = dct2[(line, oid)]  
            curs.updateRow(row)  
del curs, row

Re: Distance between points along a polyline

KirstenLawrence — Sun, 02 Aug 2015 14:06:26 GMT

Thanks for your reply that does make sense. I will test your code, thanks again.

Re: Distance between points along a polyline

KirstenLawrence — Sun, 02 Aug 2015 14:22:19 GMT

I need to sort on more than just line id, oid and distance.. as I mentioned there are multiple sets of a points along each line that need to be grouped and then have the distance calculated.. essentially I think the dct key needs to include some additional fields

Re: Distance between points along a polyline

DanPatterson_Retired — Sun, 02 Aug 2015 14:56:43 GMT

Do you have a screen grab? What sounded like a simple question now has more dimensions to it.

Re: Distance between points along a polyline

KirstenLawrence — Sun, 02 Aug 2015 16:03:19 GMT

Here is a screenshot. The different colored points represent different vehicles that are traveling along the road. I have date/time values associated with each point, and the idea is to determine the avg speed of each vehicle by using the distance between each point in a given trip (which I am roughly determining by date and time), and then calculate the time difference between points to then determine the speed. I have over a million points!

Re: Distance between points along a polyline

XanderBakker — Sun, 02 Aug 2015 17:40:55 GMT

If you are willing to share a "small" part of the data we could have a look and see what method best matches your specific question.

Re: Distance between points along a polyline

RichardFairhurst — Sun, 02 Aug 2015 20:47:59 GMT

The lines dictionary won't change, since it only has the line ID. The points dictionary can have any tuple for the key that you may want as long as the line ID is the first field in the tuple or at a known position in the key, so the look up of the line does not change. I see no real difference in the way the code would be structured other than what values reset the counter. So dct and dct2 would change but not valueDict.

In any case with over 1 million points and probably thousands of lines you would wait days or months for an embedded cursor to finish. However, with that many points and lines you may run out of memory if you process the complete set into these dictionaries in one run. You have to create a loop surrounding my code and process queries in the outer loop to segment the line and point sets into smaller groups (say iterating through ranges of 500 line IDs in the lines and points) . The dictionaries would be cleared and reset in each loop so that your memory would not run out.

Re: Distance between points along a polyline

KyleCrawford2 — Mon, 06 Mar 2017 19:25:35 GMT

When testing out your code above the script will run, but the first point values return 0 for both DistStart and DistPrev.

Why would this be?

Re: Distance between points along a polyline

XanderBakker — Tue, 07 Mar 2017 02:10:24 GMT

Do you have geographic coordinates?

Re: Distance between points along a polyline

KyleCrawford2 — Tue, 07 Mar 2017 15:18:24 GMT

Made the mistake of not correcting the geographic coordinates. Once corrected script works great thanks for sharing it.