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I am trying to make a systematic cluster sampling pattern for data collection. The sampling consist of the points placed over the landscape in 6 km span (red). From this major point, I need to create 3x3 sampling spots in 200 m span (grey), in direction towards the east and south, creating L shaped cluster of points.

I was wondering, how to make this sampling scheme in ArcGIS using ArcPy?

It is pretty straightforward to generate a set of equally distributed points over the landscape using Create Fishnet tool and set Create Label Points as TRUE. Cell height and cell width will simply be 6 km.

But do you have any suggestion, how to create set of grey points located towards east and south, in 200 m distance from each other?

I honestly even don't know where to start...

enter image description here

My sample code to generate red grid points:

import arcpy, os
from arcpy import env

# Allow files to overwrite
arcpy.env.overwriteOutput = True

# Set coordinate system of the output fishnet
arcpy.env.outputCoordinateSystem = arcpy.SpatialReference(3067)

# Define working directory
inWD = "C:/Users/data/raw"

# Define variables:
inFC = os.path.join(inWD, "myFC.shp")
outFC = os.path.join(inWD, "myFC_grid.shp")

# Create fishnet
cellSizeWidth = 6000 # 6 km
cellSizeHeight = cellSizeWidth
labels = "LABELS" # Create points in the middle of squares
desc = arcpy.Describe(inFC)  # get describe object to define extent coordinates

# Process: Create fishnet
arcpy.CreateFishnet_management(out_feature_class = outFC,
                               origin_coord = str(desc.extent.lowerLeft),
                               y_axis_coord = str(desc.extent.XMin)  + " " + str(desc.extent.YMax + 100),
                               cell_width = cellSizeWidth,
                               cell_height = cellSizeHeight,
                               number_rows = "0",
                               number_columns ="0",
                               corner_coord = str(desc.extent.upperRight),
                               labels = "LABELS",
                               template = "#",
                               geometry_type = "POLYLINE")

print "basic fishnet created"

# Import newly generated point grid data ""
red_points = os.path.join(inWD, "myFC_grid_label.shp")

# Make new freature class to add new points  
grey_points = os.path.join(inWD, "Lcluster.shp")

How to add clusters points to grey dataset?

  • 2
    It's just a little computational geometry. You don't even need to use trig functions, just use deltas on the X and Y of the reference points. An InsertCursor based on a SearchCursor is the minimum necessary code snippet, with a description of the problem you've encountered. – Vince Oct 3 at 10:54
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Given you already have your RED 6km span points which I am referring to red_points, you can do something like this to obtain your 3X3 200m grey_points.

(please, adjust the sign (+/-) as you wish to achieve your result. Also, here 200 is in meters as long as the units of your reference system is meter.)

import arcpy

red_points = "your_red_points_fc_here"
grey_points = "your_grey_points_fc_here"
sourceid_fld = "SourceID"

# add field "SourceID" to store the ID of the original (red) point
arcpy.AddField_management(grey_points, sourceid_fld, "LONG")

with arcpy.da.SearchCursor(red_points,["SHAPE@X", "SHAPE@Y", "OID@"]) as s_cur:
    with arcpy.da.InsertCursor(grey_points, ["SHAPE@X", "SHAPE@Y", sourceid_fld]) as i_cur:
        for row in s_cur:
            red_id = row[2]
            i_cur.insertRow((row[0] + 200, row[1], red_id))
            i_cur.insertRow((row[0] + 400, row[1], red_id))
            i_cur.insertRow((row[0] + 600, row[1], red_id))
            i_cur.insertRow((row[0], row[1] + 200, red_id))
            i_cur.insertRow((row[0], row[1] + 400, red_id))
            i_cur.insertRow((row[0], row[1] + 600, red_id))
  • 2
    I think this code would be improved if you copied over a red point ID to the generated grey points? So you know those grey points were generated from their respective red point. – Hornbydd Oct 3 at 16:15
  • 2
    Good point @Hornbydd. I added that in my answer. – umbe1987 Oct 4 at 7:28

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