How to do a raster layer summation by loop?

RebeccaRicker

Hey folks,

 

I work with ArcGIS Pro and Python and I need to do a Summation over 31 raster layers. I want to do it by a loop, because I need it more often.

 

 

This is what I want to loop:

 

    arcpy.env.workspace = Folder_Single_Layer_ND_as_0

   

   

    Sum_Layer_ND_as_0 = \

    Raster("/offset_0_1.tif") \

    + Raster("/offset_0_2.tif") \

    + Raster("/offset_0_3.tif") \

    + Raster("/offset_0_4.tif") \

    + Raster("/offset_0_5.tif") \

    + Raster("/offset_0_6.tif") \

    + Raster("/offset_0_7.tif") \

    + Raster("/offset_0_8.tif") \

    + Raster("/offset_0_9.tif") \

    + Raster("/offset_0_10.tif") \

    + Raster("/offset_0_11.tif") \

    + Raster("/offset_0_12.tif") \

    + Raster("/offset_0_13.tif") \

    + Raster("/offset_0_14.tif") \

    + Raster("/offset_0_15.tif") \

    + Raster("/offset_0_16.tif") \

    + Raster("/offset_0_17.tif") \

    + Raster("/offset_0_18.tif") \

    + Raster("/offset_0_19.tif") \

    + Raster("/offset_0_20.tif") \

    + Raster("/offset_0_21.tif") \

    + Raster("/offset_0_22.tif") \

    + Raster("/offset_0_23.tif") \

    + Raster("/offset_0_24.tif") \

    + Raster("/offset_0_25.tif") \

    + Raster("/offset_0_26.tif") \

    + Raster("/offset_0_27.tif") \

    + Raster("/offset_0_28.tif") \

    + Raster("/offset_0_29.tif") \

    + Raster("/offset_0_30.tif") \

    + Raster("/offset_0_31.tif") \

   

    Sum_Layer_ND_as_0.save()

 

 

I tried so far...

 

    # Those are already definite

    # TxWx = "/offset"        # I need this as a Variable.

    # Number_of_Years = 31    # I calculated this from a NetCDF

 

 

...this:

 

    arcpy.env.workspace = Folder_Single_Layer_ND_as_0

   

    for Number in range(1, int(Number_of_Years))

        Sum_Layer_ND_as_0 += Raster(TxWx + "_0_" + Number + ".tif")

 

 

...and this:

 

    arcpy.env.workspace = Folder_Single_Layer_ND_as_0

   

    x = 1

    while True:

        Sum_Layer_ND_as_0 += Raster(TxWx + "_0_" + str(x) + ".tif")

        x += int(Number_of_Years)

 

 

... and this:

 

    arcpy.env.workspace = Folder_Single_Layer_ND_as_0

  

    count = 1

   

    while count <= int(Number_of_Years):

        Sum_Layer_ND_as_0 += Raster(TXWX + "_0_" + str(count) + ".tif")

        count +=1

 

 

Nothing works. I am a very beginner in Python. I would be very grateful if anyone could help me!!!

PS.: If my question is on the wrong position or I am not supposed to ask it here, please tell me.

DanPatterson_Retired

https://community.esri.com/blogs/dan_patterson/2016/08/14/script-formatting to format your code so it is easier to read.

You need to use list rasters and sum the raster datasets using a Local sum

<SPAN class="keyword token">import</SPAN> arcpy
<SPAN class="keyword token">from</SPAN> arcpy <SPAN class="keyword token">import</SPAN> env
env<SPAN class="punctuation token">.</SPAN>workspace <SPAN class="operator token">=</SPAN> <SPAN class="string token">"C:/some_folder/a_folder_or_gdb"</SPAN>
arcpy<SPAN class="punctuation token">.</SPAN>CheckOutExtension<SPAN class="punctuation token">(</SPAN><SPAN class="string token">"Spatial"</SPAN><SPAN class="punctuation token">)</SPAN>
in_rasters <SPAN class="operator token">=</SPAN> arcpy<SPAN class="punctuation token">.</SPAN>ListRasters<SPAN class="punctuation token">(</SPAN><SPAN class="string token">"*"</SPAN><SPAN class="punctuation token">,</SPAN> <SPAN class="string token">"TIF"</SPAN><SPAN class="punctuation token">)</SPAN>&nbsp; <SPAN class="comment token"># change to suit the raster types</SPAN>
sum_cellstats <SPAN class="operator token">=</SPAN> CellStatistics_sa<SPAN class="punctuation token">(</SPAN>in_rasters<SPAN class="punctuation token">,</SPAN> <SPAN class="string token">"SUM"</SPAN><SPAN class="punctuation token">,</SPAN> <SPAN class="string token">"DATA"</SPAN><SPAN class="punctuation token">)</SPAN>&nbsp; <SPAN class="comment token"># read the help!!</SPAN>
sum_cellstats<SPAN class="punctuation token">.</SPAN>save<SPAN class="punctuation token">(</SPAN><SPAN class="string token">"C:/test/output/sum_o_rama"</SPAN><SPAN class="punctuation token">)</SPAN><SPAN class="line-numbers-rows"><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN></SPAN>

which has obviously not been tried but you can examine the various help topics to get the idea of how to work through through the process