topic Re: Looping through features in Python Questions

Looping through features

JohannesRein — Thu, 29 Mar 2012 14:08:20 GMT

Hello

I'm quiet new in python and i have the following question.

I want to export my map into jpg's with worldfile. Therfore i created a polygon-featureclass with a grid (400 objects).
As it is a little uninteresting to select and pan to every single polygon and export it, i tried to write a script doing that for me.
The problem is that i do not know how to loop through the features.

This is the code a made.

import arcpy
mxd = arcpy.mapping.MapDocument("CURRENT")
df = arcpy.mapping.ListDataFrames(mxd, "Layers")[0]
gridLayer = arcpy.mapping.ListLayers(mxd, "Grid", df)[0]
arcpy.SelectLayerByAttribute_management(gridLayer, "NEW_SELECTION", "SORT_ID = 1")
df.extent = gridLayer.getSelectedExtent(False)
df.scale = 100000
arcpy.mapping.ExportToJPEG(mxd, r"C:\Daten\Images\Image1.jpg", df, df_export_width=1600, df_export_height=1200, world_file=TRUE)
del mxd

Thank you in advance,
Jo

Re: Looping through features

DarrenWiens2 — Thu, 29 Mar 2012 14:44:18 GMT

Use a SearchCursor.

Re: Looping through features

AnthonyTimpson2 — Sat, 11 Dec 2021 13:42:54 GMT

hey there.. i made something similar a while back

basically it uses a grid to zoom to and export map blocks.

not sure if its helpful for you but maybe you can pull some parts out of it.


import arcpy
from arcpy import env
from arcpy import mapping
env.workspace = r"C:\Users\Desktop\Work\GridExportTesting"

mxd = mapping.MapDocument("Current")

fc = "Grid"
count = str(arcpy.GetCount_management(fc))

x = 1

while x < int(count) + 1:
    rows = arcpy.SearchCursor(fc, "ID = " + str(x))
    for row in rows:
        xmin, ymin, xmax, ymax  = row.shape.extent.XMin, row.shape.extent.YMin, row.shape.extent.XMax, row.shape.extent.YMax
        df = arcpy.mapping.ListDataFrames(mxd)[0]
        newExtent = df.extent
        newExtent.XMin, newExtent.YMin, newExtent.XMax, newExtent.YMax = xmin, ymin, xmax, ymax
        df.extent = newExtent
        arcpy.RefreshActiveView()
        mapping.ExportToJPEG(mxd, r"C:\Users\Desktop\Work\GridExportTesting\Grid\JPEG_" + str(x) + ".jpg", df, df_export_width=1638, df_export_height=880, world_file=True)
        print('Exported image' )
        print(x, 'of', count)
    x += 1

print("Export Complete")

Re: Looping through features

JohannesRein — Sat, 11 Dec 2021 13:42:56 GMT

Thanks for your answers, especially for the code sample.

I tried to change my code, unfortunaly it does not yet work.
The problem is the selection of the feature. In the posteted example the attribute seems to be a string. I tried with a string attribute and a number(long). None works.

import arcpy
from arcpy import env
from arcpy import mapping
env.workspace = r"C:\Daten\Test"
mxd = mapping.MapDocument("Current")
df = mapping.ListDataFrames(mxd, "Layers")[0]
fc = "Grid_100k"
count = str(arcpy.GetCount_management(fc))
x = 1
while x < int(count) + 1:
    rows = arcpy.SearchCursor(fc, "SORT_ID = " + str(x))
    for row in rows:
 df.extent = fc.getSelectedExtent(False)
 df.scale = 100000
 arcpy.mapping.ExportToJPEG(mxd, r"C:\Daten\Test\Image_" + Str(x) + ".jpg", df, df_export_width=1200, df_export_height=800, world_file=TRUE)
        print('Exported image')
        print(x, 'of', count)
    x = x + 1
print("Export Complete")

Update:

i found out that if i use a value instead of a variable, it works. But how can i use the value from the variable?

>>> arcpy.SelectLayerByAttribute_management("Grid_100k", "NEW_SELECTION", "\"SORT_ID\" = 23")
<Result 'Grid_100k'>
>>> arcpy.SelectLayerByAttribute_management("Grid_100k", "NEW_SELECTION", "\"SORT_ID\" = x")
Runtime error <class 'arcgisscripting.ExecuteError'>: ERROR 000358: Invalid expression Failed to execute (SelectLayerByAttribute).

Re: Looping through features

FabianBlau — Fri, 30 Mar 2012 10:59:29 GMT

arcpy.SelectLayerByAttribute_management("Grid_100k", "NEW_SELECTION", "\"SORT_ID\" = %i" % x)

arcpy.SelectLayerByAttribute_management("Grid_100k", "NEW_SELECTION", "\"SORT_ID\" = " + str(x))

you also can use a for-loop, for example:

for x in range(1, count+1):

Re: Looping through features

JohannesRein — Sat, 11 Dec 2021 13:42:59 GMT

The looping and nameing of the files work, but all images have the same extend.
Why does the extend not update?

It seems that ArcMap does not like the script. It crashed several times.

>>> import arcpy
... from arcpy import env
... from arcpy import mapping
... env.workspace = r"C:\Daten\Test"
... mxd = mapping.MapDocument("Current")
... df = mapping.ListDataFrames(mxd, "Layers")[0]
... fc = "Grid_100k"
... count = str(arcpy.GetCount_management(fc))
... x = 1
... while x < int(count) + 1:
...     rows = arcpy.SearchCursor(fc, "MAP = '" + str(x) + "'")
...     print(x)
...     for row in rows:
...         df.zoomToSelectedFeatures()
...         df.scale = 100000
...         arcpy.RefreshActiveView()
...         arcpy.mapping.ExportToJPEG(mxd, r"C:\Daten\Test\100k_" + str(x) + ".jpg", df, df_export_width=5866, df_export_height=3106, world_file=True)
...         print('Bild exportiert')
...         print(x, 'von', count)
...         arcpy.SelectLayerByAttribute_management(fc, "CLEAR_SELECTION")
...     x += 1
... print("Export beendet")

Re: Looping through features

MathewCoyle — Mon, 02 Apr 2012 12:49:14 GMT

You are using

df.zoomToSelectedFeatures()

But no where are you making a selection. And if you are starting with a selection in ArcMap it is getting cleared after the first iteration at this line.

arcpy.SelectLayerByAttribute_management(fc, "CLEAR_SELECTION")