ArcPy – How to Place Points Along a Line with Specific Offset Using Python/ArcPy

arcgis-10.1arcpypython

I have a street shapefile with information about the street name, house number from / to on the left side and house number from / to on the right side.

My aim is to create a point shapefile that visualizes all houses along the streets. A first prototype is already implemented. With a Search-cursor I am reading out the total number of houses by building the range by using the paramaters house number from / to on the left side and house number from / to on the right side. The total amount is divided by the length of the street so that I have a value that show me in which distance I have to place the points along the line to map all houses.

The result is that all house numbers are placed like a string of pearls.

Is there a way to place the numbers with an specific offset along the line?

The script is written in python using arcpy and ArcGIS 10.1 SP1.

Thanks!

Best Answer

In case this is helpful to others, i was able to create the following python code using arcpy which will place points at a specified interval based on an input line feature layer.

import arcpy

line_lyr = 'my_line'
pt_lyr =  "my_point"
interval = 200

insertCursor = arcpy.da.InsertCursor(pt_lyr, ["SHAPE@XY"]) # this is the pre-existing pt feature class

with arcpy.da.SearchCursor(line_lyr, ['OID@','SHAPE@','NAME']) as searchCursor: # this is the line feature on which the points will be based
    for row in searchCursor:
        lengthLine = round(row[1].length) # grab the length of the line feature, i'm using round() here to avoid weird rounding errors that prevent the numberOfPositions from being determined
        if int(lengthLine % interval) == 0:
            numberOfPositions = int(lengthLine // interval) - 1
        else:
            numberOfPositions = int(lengthLine // interval)

        print "lengthLine", lengthLine
        print "numberOfPositions", numberOfPositions
        if numberOfPositions > 0: # > 0 b/c we don't want to add a point to a line feature that is less than our interval
            for i in range(numberOfPositions): # using range, allows us to not have to worry about
                distance = (i + 1) * interval
                xPoint = row[1].positionAlongLine(distance).firstPoint.X
                yPoint = row[1].positionAlongLine(distance).firstPoint.Y
                xy = (xPoint, yPoint)
                insertCursor.insertRow([xy])

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[GIS] Creating Point Transects along line using ArcMap

you can follow these steps:

Generalize line
Densify using 50m with densify by distance parameter.
buffer the line with flat option with 10m as distance.
get the polygon result vertices using Feature vertices tool

If I haven't really understood your question, can you provide a simple drawing to explain the problem clearly.

[GIS] Selecting points on one side of the road

EDIT: I've revamped this answer after realizing that Linear Referencing supports determining the side along a line.

The best approach to this problem is to use the Linear Referencing toolbox in ArcGIS:

A linear reference system stores data using a relative position along existing line features. That is, location is given in terms of a known linear feature and a position, or measure, along it. For example, route I-10, mile 23.2, uniquely identifies a position in geographic space, and can be used instead of an x,y coordinate.

Here's how you would do it, assuming we're using the streets and lines below:

Run the Create Routes (Linear Referencing) tool with your streets as your in_line_features. Pick a unique ID field for the route_id_field parameter. You can leave all other parameters as their defaults.
Run the Locate Features Along Routes (Linear Referencing) tool with your points as the in_features, the routes we created above as the in_routes, and the street ID field as your route_id_field. You should change your radius_or_tolerance such that there's enough distance from your streets to capture all of your points. Lastly, uncheck the m_direction_offsetting parameter; this will make it such that the left/right designation is based on the digitization direction of your streets rather than the more arbitrary direction of your routes.
In your output table (shown below), you will have one row for each point. The value in the MEAS field represents the distance along the street that the point is located. The value in the Distance field represents the distance from the point to the snapped nearest location in your street, where the sign of the distance indicate the side of the street. So negative values indicate points to the left of the street and positive values indicate points to the right of the street.

Attribute table

To iterate through your left-side points, sort the table by RID and MEAS and skip positive values; do the same but reverse the sorting of MEAS and skip negative values to iterate through your ride-side points in reverse order. It's probably easiest to sort in Python:

points = []
cursor = arcpy.da.SearchCursor(eventTable, ["RID","MEAS","Distance","OBJECTID"])
for row in cursor:
    if row[2] < 0: #negative value = digitized left
        points.append((row[0],"L",row[1]))
    else: #positive value = digitized right
        points.append((row[0],"R",row[1]*-1.0)) #negate MEAS to reverse direction
points.sort() #will break ties when sorting using 2nd or 3rd element in tuple
print [point[3] for point in points]

This results in our points sorted by street ID, then left side from start to end, then right side from end to start:

[9, 11, 12, 10, 8, 1, 4, 6, 5, 3, 2, 7]

Best Answer

Related Solutions

[GIS] Creating Point Transects along line using ArcMap

[GIS] Selecting points on one side of the road

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