topic Re: select random points in Geoprocessing Questions

select random points

LoriEpstein — Fri, 31 Jan 2014 03:19:39 GMT

Hey all!

I have sounding data with tens of thousands of points per feature. I need to reduce the points significantly in density, and was hoping there was a way to randomly select points through an arcmap tool. While the create random points tool does what I need, it does not seem to maintain the attribute data (eg. depth) that I need with each point. Any suggestions?

Re: select random points

DanEvans — Fri, 31 Jan 2014 10:29:37 GMT

I think the Create Random Points tool does just that: creates new points randomly, rather than selecting existing points randomly.

You could try adding a new field to your existing points, then calculating a random 1 or 0 for each point, then just select out the 1s. I think it could still be a bit random how many 1s you get though, it might not reduce the points by much.

If there was a certain factor you wanted to reduce the data by, and as long as the OBJECT_IDs aren't sorted in any way, you could calculate a modulo in your field, e.g. to just pick out every 10th point, you'd calculate OBJECT_ID % 10 (which would give you the remainder left if you divided the OBJECT_ID by 10) and select all the 0s in that field.

Hope that makes sense, if not let me know and I will try to explain better!

Dan

Re: select random points

SteveLynch — Fri, 31 Jan 2014 11:35:36 GMT

Subset Features is designed to do that.

Re: select random points

michaelcollins1 — Fri, 31 Jan 2014 11:38:04 GMT

Try this free tool.

http://www.arcgis.com/home/item.html?id=ecbe1fc44f35465f9dea42ef9b63e785

And the manual.

http://www.arcgis.com/home/item.html?id=f7289cfc69204aa688e8c7c739fc0901

Re: select random points

michaelcollins1 — Fri, 31 Jan 2014 11:39:06 GMT

Subset Features is designed to do that.

*** Requires Geostatistical Analyst ***

Re: select random points

GerryGabrisch — Sat, 11 Dec 2021 15:42:53 GMT

This code will populate an existing attribute with a random number. Run the script. Then, for example, select values less than 0.2 to select about 20% of your points.

#Populates an existing attribute with a randomly generated value 

try:
    import operator, os, random, traceback, sys, arcpy
    arcpy.AddMessage("Adding random numbers to an existing attribute.")
    arcpy.AddMessage("Copyright 2011, Gerry Gabrisch, gerry@gabrisch.us")

    #Path to the feature class.
    fc = arcpy.GetParameterAsText(0)
    #The Attribute to populate...
    attribute = arcpy.GetParameterAsText(1)
  
    uc = arcpy.UpdateCursor(fc)
    for row in uc:
        x = random.random()
        row.setValue(attribute, x)
        uc.updateRow(row)
    arcpy.AddMessage("Done")
    
except arcpy.ExecuteError: 
    msgs = arcpy.GetMessages(2)
    arcpy.AddError(msgs)  
    arcpy.AddMessage(msgs)
except:
    tb = sys.exc_info()[2]
    tbinfo = traceback.format_tb(tb)[0]
    pymsg = "PYTHON ERRORS:\nTraceback info:\n" + tbinfo + "\nError Info:\n" + str(sys.exc_info()[1])
    msgs = "ArcPy ERRORS:\n" + arcpy.GetMessages(2) + "\n"
    arcpy.AddError(pymsg)
    arcpy.AddError(msgs)
    arcpy.AddMessage(pymsg + "\n")
    arcpy.AddMessage(msgs)

Re: select random points

FourCornersMapping — Mon, 16 May 2022 15:54:28 GMT

I'm guessing you're eight years beyond needing an answer to this question. But here is some more info: In ArcGIS Pro 2.8, you can use the Create Random Points tool to select a subset, using your original point feature class as the "Constraining Feature Class". The attributes are not preserved in the output as you note; however, you can join via the CID field, matching to the OID in the original data source.

Re: select random points

Anonymous User — Tue, 13 Sep 2022 21:46:59 GMT

Or select by location using the new feature as the intersecting feature!