topic How to count the adjacent cells that have a different value in a raster dataset? in ArcGIS Spatial Analyst Questions

How to count the adjacent cells that have a different value in a raster dataset?

MarkLimb — Thu, 09 Aug 2018 02:18:35 GMT

Hi,

I'm using a raster dataset and I'm trying to determine a value for land use adjacency as used by Stathakis & Tsilimigkas (2014) (Measuring the compactness of European medium-sized cities by spatial metrics based on fused data sets. International Journal of Image and Data Fusion, 6(1), 42-64. doi:10.1080/19479832.2014.941018)

This involves counting the number of adjacent cells that have a value different to the centre cell. The attached image illustrates this concept.

It needs to return a new raster dataset where the value of each cell equals this count.

Can anyone suggest a method for doing this in ArcMap 10?

Thank you!

EDIT:

Dan, you're an absolute legend! Amazing dedication and perseverance to assist a total stranger on the other side of the world. Thank you so much for all your effort on this!

Just to update, the main issues experienced had much to do with a combination of differences in arcmap 10.3's and ArcGIS Pro's arcpy, and some major changes in numpy that is used by python 2.7 and python 3.6. Dan worked through them and ended up producing the Toolbox/Script I've attached to this edited post. As a final tip, make sure you run the script in a blank dataframe. You will need to manually set the projection of the final output.

Re: How to count the adjacent cells that have a different value in a raster dataset?

DanPatterson_Retired — Thu, 09 Aug 2018 02:36:41 GMT

Focal Statistics—Help | ArcGIS Desktop using variety

….if you are using arcmap or ArcGIS pro (need spatial analyst extension)

numpy if you need more than the number of different values within the neighborhood (ie count by the different classes)

Re: How to count the adjacent cells that have a different value in a raster dataset?

MarkLimb — Thu, 09 Aug 2018 03:17:35 GMT

Thanks Dan,

That's the tool I was looking for!

Doesn't quite get there though as I'm looking for a count of the number cells in the neighborhood that are different to the centre cell. The VARIETY statistics type only tells me the count of the unique values (which would also include the value of the centre cell).

Not sure what you mean by numpy? Do you mean this: NumPy — NumPy ? I've never used it before, are you aware of any useful guides that would help with what I'm trying to do?

Re: How to count the adjacent cells that have a different value in a raster dataset?

DanPatterson_Retired — Sat, 11 Dec 2021 10:46:51 GMT

I think this is what you want.

Don't worry about how I got it for now, but it uses a moving/sliding 3x3 window on a "raster" as an array

See if this is what you really want...

# ---- consider this small 'raster'
input array
[[1 5 2 1 2 5]
 [3 5 3 3 6 6]
 [3 9 8 5 1 3]
 [1 5 8 4 9 8]
 [4 7 3 8 4 2]
 [0 9 8 4 4 6]]

# ---- produce a moving/rolling version using a 3x3 kernel
#      the first row only...

strided array... first block
[[[1 5 2]
  [3 5 3]
  [3 9 8]]

 [[5 2 1]
  [5 3 3]
  [9 8 5]]

 [[2 1 2]
  [3 3 6]
  [8 5 1]]

 [[1 2 5]
  [3 6 6]
  [5 1 3]]]

# ---- look at them individually and calculate the 'statistic'
sub array
[[1 5 2]
 [3 5 3]
 [3 9 8]] ... number different than 5 ... 7
sub array
[[5 2 1]
 [5 3 3]
 [9 8 5]] ... number different than 3 ... 7
sub array
[[2 1 2]
 [3 3 6]
 [8 5 1]] ... number different than 3 ... 7
sub array
[[1 2 5]
 [3 6 6]
 [5 1 3]] ... number different than 6 ... 7

# ---- continue on
‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Re: How to count the adjacent cells that have a different value in a raster dataset?

MarkLimb — Thu, 09 Aug 2018 11:34:46 GMT

Yep, that's it!

Re: How to count the adjacent cells that have a different value in a raster dataset?

DanPatterson_Retired — Thu, 09 Aug 2018 11:57:18 GMT

Ok.. before we get to using numpy, see if you can use the focal statistics variety with an irregular neighborhood

NbrIrregular—Spatial Analyst module | ArcGIS Desktop

effectively you need a kernel file of form

3 3

1 1 1

1 0 1

1 1 1

KernelFile

The irregular inKernelFile is an ASCII text file that defines the shape of an irregular neighborhood. A value of 0 for a cell position indicates that the cell is not a member of the neighborhood, and a nonzero number at a corresponding cell's position indicates that the cell value be included as a member of the neighborhood.

File

which should blot out the core/focal cell

See

Focal Statistics—Help | ArcGIS Desktop

So as an example from PRO

I spent an inordinate amount of time making the kernel file to save you some time

Give the standard tool with the irregular kernel a shot otherwise I will have to put a short script together for you

PS, statistics type should be variety... didn't have any rasters to test on.. that is your job

Re: How to count the adjacent cells that have a different value in a raster dataset?

MarkLimb — Fri, 10 Aug 2018 00:45:56 GMT

Thank you so much for your help Dan, I really appreciate the effort! The kernal is working well in terms of selecting the right neighbourhood, however the statistics aren't. I was thinking of using the annulus to do this, but your idea is more precise.

Basically this is because I need the count of the surrounding cells that are different to the centre cell. The VARIETY statistics option only counts number of unique values. Also, it's currently counting cells that are the same as the centre cell.

The crudely drawn attached image demonstrates the current results vs. what I require. The underlying image is an extract of my raster data.

The Results table show the results returned by the Focal Stats tool for the grid I've drawn in red.

The Required table shows the results I would expect using the method described by Stathakis & Tsilimigkas.

Re: How to count the adjacent cells that have a different value in a raster dataset?

DanPatterson_Retired — Fri, 10 Aug 2018 01:23:42 GMT

so the kernel is basically calculating for 1 cell. with the image you showed above, you have no difference in the values around the kernel/core cell... so cell B1 is giving you 1, where as it should give you 0.

But!!! a variety of 1, implies no variation since the core cell is assigned 0... it may be as simple subtracting 1 from the focal statistics.

Cells b1 to C2 support this, but if you are showing results from the edge of a raster all bets are off since some form of edge fudging may be occurring.

If you could zip and attach a small raster *tif for further inspection, I can look deeper and produce numpy variants like I have shown before... so make sure that those are good... but do the assessment a couple of cells in from edges.

Re: How to count the adjacent cells that have a different value in a raster dataset?

MarkLimb — Fri, 10 Aug 2018 02:09:30 GMT

I don't think just subtracting will work as it's not going to capture what I show in in cells A0 & B0.

The sample I provided above isn't from the edge, it's from the centre of the raster (there are spots throughout that have no data (typically from roads), and this is intentional. Idea is for areas of no data to be ignored.

Please find a sample attached as requested.

Re: How to count the adjacent cells that have a different value in a raster dataset?

DanPatterson_Retired — Fri, 10 Aug 2018 02:24:44 GMT

A0 is surrounded by 5 green and 2 reddish... It's variety is 2, the 'required' version is the frequency count like I showed in one of my numpy examples.

Soooo it sounds like you want the variety (2) but the count for the classes making up the one that is 'different' from the core/focal cell.

That is doable, but if you could articulate the algorithm, I can implement it in numpy...

all that is needed is a sample (small) raster zipped and attached to your original thread for testing. You can do hand calculations, and I can run through variants oke the ones I have shown.

Re: How to count the adjacent cells that have a different value in a raster dataset?

MarkLimb — Fri, 10 Aug 2018 02:38:33 GMT

That's right: for each cell, I need a count of the number of surrounding cells that have a different value to the core (excluding cells with no data).

For the sample you require... do you a raster that includes the input data and another that includes the solved data for that area? If so, what grid size do you require?

Re: How to count the adjacent cells that have a different value in a raster dataset?

DanPatterson_Retired — Sat, 11 Dec 2021 10:46:54 GMT

something to amuse you in the interim.... based on your example

input array
[[1 1 1 2 2]
 [1 2 2 2 2]
 [1 2 2 2 2]
 [1 2 2 2 2]]
strided array... 
[[[[1 1 1]
   [1 2 2]
   [1 2 2]]

  [[1 1 2]
   [2 2 2]
   [2 2 2]]

  [[1 2 2]
   [2 2 2]
   [2 2 2]]]


 [[[1 2 2]
   [1 2 2]
   [1 2 2]]

  [[2 2 2]
   [2 2 2]
   [2 2 2]]

  [[2 2 2]
   [2 2 2]
   [2 2 2]]]]
sub array
[[1 1 1]
 [1 2 2]
 [1 2 2]] ... number different than 2 ... 5
sub array
[[1 1 2]
 [2 2 2]
 [2 2 2]] ... number different than 2 ... 2
sub array
[[1 2 2]
 [2 2 2]
 [2 2 2]] ... number different than 2 ... 1
sub array
[[1 2 2]
 [1 2 2]
 [1 2 2]] ... number different than 2 ... 3
sub array
[[2 2 2]
 [2 2 2]
 [2 2 2]] ... number different than 2 ... 0
sub array
[[2 2 2]
 [2 2 2]
 [2 2 2]] ... number different than 2 ... 0

‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Re: How to count the adjacent cells that have a different value in a raster dataset?

DanPatterson_Retired — Fri, 10 Aug 2018 02:57:59 GMT

Mark, I don't need any specific cell size. The sample you sent is sufficient, I can make my array from it.

Tonight...

Re: How to count the adjacent cells that have a different value in a raster dataset?

MarkLimb — Fri, 10 Aug 2018 02:59:29 GMT

Yep, that's exactly what I'm looking for.

Re: How to count the adjacent cells that have a different value in a raster dataset?

DanPatterson_Retired — Fri, 10 Aug 2018 04:30:25 GMT

I had to trim off a lot of nodata area to get to the crux of the data… a couple of visuals.

I trimmed, ran the 'algorithm', made a fishnet so you could see cell outlines, and zoomed into a random area for you to have a look at. I then converted the 'result' to a point file so that I could use labelling as well. So if the colors aren't great, you dan check a cell value against the number.

The first image is the original values.

The second is the number of cells around the original cell that are different.

Check the logic.

EDIT See images in a subsequent thread

Re: How to count the adjacent cells that have a different value in a raster dataset?

MarkLimb — Fri, 10 Aug 2018 05:17:19 GMT

Thank you very much for this Dan, very clearly explained!

Unless I'm missing something, I'm not sure if this is quite doing it though? Two issues I can see:

Values are being calculated for cells with no data (I'm assuming that's what the black is in the first image?). For example cell 7,B (x,y). It's a null cell but appears to be calculating the two adjacent red cells. The no data cells should be skipped
Others don't seem to be working as expected. For example, cell 8,B is shown as 5 when 0 was expected. Or cell 8,F which is 3, when 0 would be expected. Cell 2,H is 5 when 3 was expected

Mark

Re: How to count the adjacent cells that have a different value in a raster dataset?

DanPatterson_Retired — Sat, 11 Aug 2018 05:25:40 GMT

Mark... forget the other images.

Sorry for the delay (holidays.. sort of)

So, nulls have been removed as being a different value around the focal cell... wasn't sure about that one.

That affects the results.

A newly clipped sample and result... have a gander

Now the result... notice that most of the areas are classes as 0 difference which is to be expected, now that null values are removed from consideration.

Re: How to count the adjacent cells that have a different value in a raster dataset?

MarkLimb — Mon, 13 Aug 2018 00:34:47 GMT

That's the ticket, perfect!

Many thanks Dan! The question now of course is... how did you do it?

Re: How to count the adjacent cells that have a different value in a raster dataset?

DanPatterson_Retired — Mon, 13 Aug 2018 01:47:24 GMT

Just got back, so I am putting it into a useable script form in a toolbox, but I only use PRO, so you will be the tester of whether saving a toolbox to an ArcMap version actually works... so ArcMap 10.????? after the dot would help

Re: How to count the adjacent cells that have a different value in a raster dataset?

MarkLimb — Mon, 13 Aug 2018 01:54:31 GMT

Hi Dan,

I'm not in the office today so not certain... I think it is 10.3 but will need to confirm.

Many thanks again!