Is there a tool or script out there than can be used to create points along a polyline based on a distance in table?
What is the table structure? If they were easily spaced, then a simple densification would work, but obviously this is not the case
You could also look at this thread and the help file on discussion on linear referencing
Thanks for your reply. I will get more specific. I'm working with Sewer CCTV and Esri had created a script to use this data but it was having a lot of issues, mostly because it was the first release. They have reworked some things and I haven't got a chance to get back to it yet but hopefully that helps. If not, I may turn to linear referencing. However, I worry that when I rebuild the network that the routes would also be updated, perhaps I am wrong about how this works.
Normally, the Routes don't rebuild unless you make them rebuild. As a result, holding positions through events can be a challenge. But you can convert events to true points that are not relative to the route and then they will hold their position even if the route changes or you can calculate before and after XY coordinate values into the events and compare then to detect changes and make updates as necessary.
The Roads and Highways Extension does maintain updates as edits are made to Centerlines and registered event tables are synchronized with the edits according to the rules you define. But without that extension the event tables and routes can get out of sync.
That was my main fear of doing that. I actually checked with my account manager on that extension and wow...too pricey for my blood.
What Richard says is true, however, I do not find this a challenging thing to overcome (the price of the Highways Extension is). A general rule, the events will change location if you added length to the beginning of the route or some sort of alignment has occurred. When these conditions occur, I simply:
This is not really a hard process.... Our LRS rarely changes so this is not something I have to do a lot.
Back to the original question, you can fairly easily place a point along a line at a feature-specific distance using arcpy geometry objects - specifically, the positionAlongLine method in the Polyline object.
Returns a point on a line at a specified distance from the beginning of the line.
what about a specific distance rather than a percentage?
Since I use Linear Referencing I have no use for this function. It performs approximately 50 times slower than an LR event layer from a table based on other geometry operations I have tried. Your welcome to pursue it, but unless you can get 120K points to draw in under 30 seconds, I have you beat with my LR event layer.
Josh, positionAlongLine defaults to using an absolute distance. If you want to use a percentage, you would change the optional second parameter to True (I think).
Richard, this is clearly just one method, and for me using Python geometry objects is more flexible than finding the fastest pre-made tool. IMHO, it also directly answers the question, "how do I create points along a polyline based on distance," better than "read the help on Linear Referencing".
As Darren says it is easy it is fairly easy.. As an example, I have an example of a function that I use in the field calculator that allows you to get the X or Y coordinate tool for polylines or polygon perimeters. It is much like the Calculate Geometry tool but allow for some fine tuning of the position and in what format to return (many threads contributed to its final form). But in any event, it could easy be put into use. The "shape" variable is either a shape like when running through a cursor or the shape field (!Shape!, usually) when using the field calculator
def pnt_along(shape, value, use_fraction, XorY): """ :Required: :-------- : shape field, value (planar 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. : :Useage: For field calculator... :------ : pnt_along(!Shape!, 100, False, 'X') #eg. X coordinate 100 m from start point : :Notes: Project the data prior to using absoulte distances. :----- : """ XorY = XorY.upper() if use_fraction and (value > 1.0): value = value/100.0 if shape.type.lower() == "polygon": shape = shape.boundary() pnt = shape.positionAlongLine(value, use_fraction) if XorY == 'X': return pnt.centroid.X else: return pnt.centroid.Y <SPAN class="line-numbers-rows"><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN><SPAN></SPAN></SPAN>
in any event, enjoy... and thanks to the ideas of its predecessors
Absolute distances with the positionAlongLine method always have to be in meters. LR by default uses the length units of the original line when the Length option is checked in the Create Routes tool and that tool has the option to apply a conversion factor that can convert the measures to any units of measurement desired.
Wow, looks like I opened a can of worms on that one. They've released a new version of the CCTV processor that I am going to try out.
Grief Richard....No the function isn't restricted on one planar measure. It uses the coordinate system of the incoming shape.
However, since you bring it up, It is common only to use projected data for such a function, since the position between two geodesic points (ie Long/Lat coordinates) need not be on the imaginary line connecting them but on the geodesic line.
There are other examples for this, but Josh's main issue is getting off topic.
Also, in Canada, we use metres (Canadian and world-wide spelling) or meters (US spelling) and my examples for teaching purposes and serves as a gentle reminder to ensure to use planar coordinates when trying to determine geometric properties of spatial features.
Sorry Josh...back to you
Richard, the units for positionAlongLine are determined by the spatial reference of the Polyline object. For example, the following snippet places a point 1000 feet from the start of the line, because "kentucky_line" uses the Kentucky State Plane US Feet projection:
>>> for row in arcpy.da.SearchCursor("kentucky_line", ["SHAPE@"]): ... point = row[0].positionAlongLine(1000) >>> arcpy.CopyFeatures_management(point, 'in_memory\point')
Sorry about my bad assumption. The descriptions of some of the methods in the Geometry help suggest that they only return values in meters (getLength) and square meters (getArea) and the help document is far from clear about how any of the other functions behave with regard to units, so I thought this method might have a similar restriction. Anyway, I grant that LR and the postionAlongLine geometry function are equal as far as unit handling.
Darren: I am curious. What is the performance of your code example? How many points does it generate and how long does it take?
you acn use this python script to generate point along polyline . here i have taken distance 50.
import arcpy, math, datetime, numpy
print ("starting")
start = datetime.datetime.now() # for calculating time of process
midpoint = "E:/test/testShape.shp"
polyline = "c:/arcgis/MyLR/baseroads.shp"
#housekeeping
with arcpy.da.SearchCursor(polyline, "SHAPE@") as in_cursor, \
for row in in_cursor:
midpoint = row[0].positionAlongLine(50)
out_cursor.insertRow([midpoint])
You can use the geoprocessing tool Create RouteEvent layer
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