topic Re: calculate central point feature within each grid cell.? in Python Questions

calculate central point feature within each grid cell.?

YamMagar — Thu, 06 Feb 2014 14:39:53 GMT

Hello,

I have points scattered over grid cell (fishnet), would like to calculate a central point for each cell. How do I do it simpler way in python?

Thanks.

Re: calculate central point feature within each grid cell.?

JoshuaChisholm — Sat, 11 Dec 2021 15:10:09 GMT

Hello Milan,

What format is your grid (fishnet) in? Polygons? Raster? Polylines?

If your grid is a series of separate polygons you can check out the Feature To Point tool. This tool can be used in python, model builder or run manually.

Python:

import arcpy
inFC=r"C:\Path\To\Grid.shp"
outFC=r"C:\Path\To\NewPoints.shp"
arcpy.FeatureToPoint_management(inFC,outFC)

Let me know how it goes!
~Josh

Re: calculate central point feature within each grid cell.?

YamMagar — Thu, 06 Feb 2014 15:30:01 GMT

Hi Josh,

Thanks for your tips. Looks like it creates a centroid, but I am expecting a mean point for each cell out of multiple points within a cell. Fishnet is a polygon (vector). Thanks.

[ATTACH=CONFIG]31182[/ATTACH]

Re: calculate central point feature within each grid cell.?

JoshuaChisholm — Thu, 06 Feb 2014 17:10:46 GMT

Ok, I think I understand what you're trying to do now. Let me make sure I got it right:
You want to somehow merge all the points within a given grid to one central point (based on the containing grid).

Next question: how do you want to combine the fields of all those points into one?
For example, if a grid has three points and those points have the values of 11, 74 and 36; should the central point have a value of 121 (sum), 40.333 (average), 36 (median) or something different? If there are string fields, how do you want to handle those?

We should be able to do everything with python.

Re: calculate central point feature within each grid cell.?

YamMagar — Thu, 06 Feb 2014 17:57:32 GMT

Thanks for your follow up, really appreciated !. These points are nothing to do with weight, they are just Lat/Long points feature. I just want to calculate a central point based on their location within a grid. Some grids just have one point which is fine ( I want to leave them as they are), but would like to calculate a central point for those grids that has more then one point.

Re: calculate central point feature within each grid cell.?

DarrenWiens2 — Thu, 06 Feb 2014 18:32:25 GMT

1.) Spatial Join to assign grid ID to points
2.) Mean Center (case = grid ID)

Re: calculate central point feature within each grid cell.?

JoshuaChisholm — Thu, 06 Feb 2014 18:38:11 GMT

Ohhh, now I get it (i think).

You should be able to do that with two tools. You can do this with or without python.

First, you want to do a spatial join to get the polygon grid data to a point level.

Target Features: point data (you can point to either the feature class of the feature layer)

Join Features: grid (fishnet) data (you can point to either the feature class of the feature layer)

Output Feature class: pick a location

Join Operation: JOIN_ONE_TO_MANY (there can be many points inside each grid)

Uncheck the "Keep All Target Features" (we don't want to calculate the central point for points that don't fall into a grid)

In python you would use this line:

arcpy.SpatialJoin_analysis(r"C:\Path\To\Points.shp",r"C:\Path\To\Grid.shp",r"C:\Path\To\PointsWithGridData.shp","JOIN_ONE_TO_MANY","KEEP_COMMON")

Secondly, use Mean Center tool to get your central points.

Input Feature Class: The feature class you created above (you can point to either the feature class of the feature layer)

Output Feature Class: pick a location

Case Field: pick a unique field from the grid feature class. If you have a grid name field, choose that one. If you can't find one, you can just choose 'JOIN_FID'. 'JOIN_FID' will work but will mean the resulting points will only have a number to be identified/labeled by.

In python you would use this line:

arcpy.MeanCenter_stats(r"C:\Path\To\PointsWithGridData.shp",r"C:\Path\To\CentralPoints.shp","#","JOIN_FID")

Let me know if it works. Good luck!

Re: calculate central point feature within each grid cell.?

YamMagar — Thu, 06 Feb 2014 19:47:54 GMT

Thank you Darren and Josh ! It worked well.