Python script/expression for field calculator for converting bearings to directions?

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09-22-2016 10:03 AM
bobcostanza
New Contributor II

I have a double field with bearings/azimuths (numbers) and I need them in letter directions: N, NE, NW,etc. I would like to calculate them in  a new field.  I have searched high and low for the code to use in the field calculator but I have failed to figure it out.

Thanks,

Bob

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1 Solution

Accepted Solutions
DanPatterson_Retired
MVP Esteemed Contributor

a head messer

import numpy as np
global a
global c
a = np.array([ 45., 135., 225., 315., 360])
c = np.array(['N', 'E', 'S', 'W', 'N'])
def compass(angle):
    """ test """
    return c[np.digitize([angle], a)]

useage

compass(!YourFieldNameHere!)  # using the python processor of course

although I hate to use globals.

Now when you do this in python (TableToNumPyArray or FeatureClassToNumPyArray) you can get the results quickly or as a demo script

    angles = [0, 44, 46, 134, 136, 224, 226, 314, 316, 359]
    for i in angles:
        print("{} => {}".format(i, compass(i)))

Yielding... 

0 => ['N']
44 => ['N']
46 => ['E']
134 => ['E']
136 => ['S']
224 => ['S']
226 => ['W']
314 => ['W']
316 => ['N']
359 => ['N']

Why use this?  Because the next thing is that someone will want to narrow down things into 22.5 degree chunks (ie NNW or NNE etc etc)

To change the above, you just need to fiddle in some more compass bearings and compass designators.

View solution in original post

27 Replies
JakeSkinner
Esri Esteemed Contributor

Hi Bob,

If the lines represent the bearings/azimuth correctly you can add COGO fields to the feature class and then update the COGO attributes.

bobcostanza
New Contributor II

Thanks,

I am not working with points. I think I am in need of an if/else python

script.

Bob

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BlakeTerhune
MVP Regular Contributor

The COGO stuff Jake Skinner‌ posted is worth looking into. If you just want something quick and custom, could expand on logic like this?

if in_field_val >= 0 and in_field_val < 90:
    out_dir = "N"
elif in_field_val >= 90 and in_field_val < 180:
    out_dir = "E"
elif in_field_val >= 180 and in_field_val < 270:
    out_dir = "S"
elif in_field_val >= 270 and in_field_val < 360:
    out_dir = "W"
else:
    out_dir = None
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bobcostanza
New Contributor II

Blake,

so, I don't need to check off the code block in field calculator, i.e., I

don't need the pre-logic script code and the other part?

thanks,

Bob

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DanPatterson_Retired
MVP Esteemed Contributor

when you are using a code block, then you need to show the code block just like in the picture

Calculate Field examples—Help | ArcGIS for Desktop in the code block section.

I use python as everyone will at some stage

DanPatterson_Retired
MVP Esteemed Contributor

a head messer

import numpy as np
global a
global c
a = np.array([ 45., 135., 225., 315., 360])
c = np.array(['N', 'E', 'S', 'W', 'N'])
def compass(angle):
    """ test """
    return c[np.digitize([angle], a)]

useage

compass(!YourFieldNameHere!)  # using the python processor of course

although I hate to use globals.

Now when you do this in python (TableToNumPyArray or FeatureClassToNumPyArray) you can get the results quickly or as a demo script

    angles = [0, 44, 46, 134, 136, 224, 226, 314, 316, 359]
    for i in angles:
        print("{} => {}".format(i, compass(i)))

Yielding... 

0 => ['N']
44 => ['N']
46 => ['E']
134 => ['E']
136 => ['S']
224 => ['S']
226 => ['W']
314 => ['W']
316 => ['N']
359 => ['N']

Why use this?  Because the next thing is that someone will want to narrow down things into 22.5 degree chunks (ie NNW or NNE etc etc)

To change the above, you just need to fiddle in some more compass bearings and compass designators.

bobcostanza
New Contributor II

Isn't a if/else statement possible?

I need to look this over more.

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DanPatterson_Retired
MVP Esteemed Contributor

you copy the first block i posted just like you would any function in the codeblock area (including all lines 1-8)

Then I gave you the expression box syntax (make sure you use the python parser in the field calculator), and replace the !YourFieldNameHere! with your field name surrounded by exclamation marks..

The other two blocks are just demo scripts I used on my iThingy  with Pythonista version 3.5, but it should still work with python 2.7

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DarrenWiens2
MVP Honored Contributor

Very similar to other solutions that could be adapted to the field calculator:

Python parser

Expression:

myfunc( !bearing! )

Codeblock:

dict = {'N':[0,90],'E':[90,180],'S':[180,270],'W':[270,360]}
def myfunc(bearing):
  for k,v in dict.iteritems():
    if bearing >= v[0] and bearing < v[1]:
      return k