Updating table fields from a raster file

[RenanBarroso]

Hi there! I have some raster files in grid format with signed integer pixels in which I want to add some fields in their table then compute values with some formulas in the new fields. I managed to add the fields but I'm struggling with the second part. I tried with arcpy.da.UpdateCursor but it returns a RuntimeError: 'in_table' is not a table or a feature class. It seems clear for me that I can not use this function with raster file. Is there a way to compute the values directly in the raster or do I have to try a different approach? How?

The code is:

import arcpy as ap
import os
import random_function as rf # change name after
from arcpy.sa import *

if ap.CheckExtension('Spatial') == 'Available':
     ap.CheckOutExtension('Spatial')
else: 
     print('Spatial Analyst extension is not available')

# Setting environments & paths
ap.env.workspace = os.path.join("D:\\", "master", "_thesis_data")
ap.env.scratchWorkspace = os.path.join(ap.env.workspace, "temp")
ap.env.overwriteOutput = True
inp_ws = ap.env.workspace
temp_ws = ap.env.scratchWorkspace 
lu_folder = os.path.join(inp_ws, "lu")

lu_scenarios = []
for dirpath, dirnames, filenames in ap.da.Walk(lu_folder, datatype='RasterDataset'):
     for f in filenames:
          lu_scenarios.append(os.path.join(dirpath,f))

# Setting input data 
climate = Raster("climate_c")
clim_soil = Raster("rc_climsoil_c")
tbl_uSOCr = os.path.join(inp_ws, "uSOCr.txt")
tbl_uSOCf = os.path.join(inp_ws, "uSOCf.txt")
tbl_uBCi = os.path.join(inp_ws, "uBCi.txt")

for (sc, lu_sc) in enumerate(lu_scenarios):
     lu = Raster(lu_sc)
     clim_lu = climate + lu
     soc_f1k = ReclassByTable(clim_lu, tbl_uSOCf, "id", "id", "soc_factor")
     soc_r1k = ReclassByTable(clim_soil, tbl_uSOCr, "id", "id", "soc_ref")
     soc_1k = (soc_f1k*soc_r1k)/1000 
     bc_1k = ReclassByTable(clim_lu, tbl_uBCi, "id", "id", "bcs")          
     tc_1k = (soc_1k + bc_1k)
     tc_1k_new_fields = ["tc", "tot_ha", "tot_cs"]
     for field in tc_1k_new_fields:
          ap.AddField_management(tc_1k, field, "FLOAT", 12, 4)
     with ap.da.UpdateCursor(tc_1k, "*") as cursor:
          tc_all_fields = [f.name for f in arcpy.ListFields(tc_1k)]               
          VALUE, COUNT, tc, tot_ha, tot_cs = row[1], row[2], row[3], row[4], row[5]
                 for row in cursor:
                    tc = VALUE/1000 
                    tot_ha = COUNT*2500  
                    tot_cs = tc*tot_ha  
                    cursor.updateRow(row)                                   
                    
     if ap.GetRasterProperties_management(tc_1k, "ALLNODATA"):
          tc_1k.save(temp_ws + "\\" + "0sc" + str(sc) + "_tc" + str(mc_counter+1)) # ==> TESTING DATA!!!
     print tc_1k‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Thanks again!

[DanPatterson_Retired]

You could export the raster table to a standalone table or a table in a geodatabase

[RenanBarroso]

And how can I do that in arcpy? I was also wondering if there is a way to have the raster attribute tables in numpy array. I have tried the RasterToNumpyArray, but without success. The thing I want to do seems quite easy but I'm really struggling with it =/.

Thanks again!

[DanPatterson_Retired]

I use RasterToNumPyArray all the time.  What was your problem.

pth = r"C:\Temp\dem.tif"


pth = r"C:\Temp\myarray.tif"

a = RasterToNumPyArray(pth)

a.shape
Out[7]: (50, 50)

a
Out[8]: 
array([[68, 33, 78, ..., 53, 39, 89],
       [87, 88, 22, ..., 75,  7, 96],
       [69, 51, 77, ..., 84, 69, 83],
       ...,
       [73,  0,  1, ..., 29, 25, 88],
       [81, 60, 94, ..., 28, 23, 68],
       [47,  5, 55, ..., 19, 78,  9]])

a - a.mean()
 
array([[ 17.9472, -17.0528,  27.9472, ...,   2.9472, -11.0528,  38.9472],
       [ 36.9472,  37.9472, -28.0528, ...,  24.9472, -43.0528,  45.9472],
       [ 18.9472,   0.9472,  26.9472, ...,  33.9472,  18.9472,  32.9472],
       ...,
       [ 22.9472, -50.0528, -49.0528, ..., -21.0528, -25.0528,  37.9472],
       [ 30.9472,   9.9472,  43.9472, ..., -22.0528, -27.0528,  17.9472],
       [ -3.0528, -45.0528,   4.9472, ..., -31.0528,  27.9472, -41.0528]])‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

[RenanBarroso]

Thank you! Now it is working and I've changed all my raster processing to NumpyArray. Much better! 

[DanPatterson_Retired]

I have lots of NumPy examples on my blog post if you are interested in numpy functionality with arcpy and other modules.

[XanderBakker]

The cursors in the da module do not provide access to raster attribute tables (RAT). The old cursors do. Although I have never used it to write to a RAT, I have used the old cursors to read from it...

https://community.esri.com/message/355845?commentID=355845#comment-633411