topic Re: Python script/expression for field calculator for converting bearings to directions? in Geoprocessing Questions

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

bobcostanza — Thu, 22 Sep 2016 17:03:16 GMT

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

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

JakeSkinner — Thu, 22 Sep 2016 17:14:04 GMT

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.

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

BlakeTerhune — Sat, 11 Dec 2021 17:39:18 GMT

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

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

DanPatterson_Retired — Sat, 11 Dec 2021 17:39:21 GMT

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.

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

bobcostanza — Thu, 22 Sep 2016 19:39:21 GMT

Thanks,

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

script.

Bob

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

bobcostanza — Thu, 22 Sep 2016 19:47:09 GMT

Isn't a if/else statement possible?

I need to look this over more.

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

DanPatterson_Retired — Thu, 22 Sep 2016 19:51:27 GMT

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

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

bobcostanza — Thu, 22 Sep 2016 19:54:21 GMT

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

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

DanPatterson_Retired — Thu, 22 Sep 2016 19:58:36 GMT

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

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

DarrenWiens2 — Sat, 11 Dec 2021 17:39:23 GMT

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

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

DanPatterson_Retired — Thu, 22 Sep 2016 20:09:50 GMT

Darren... just shift your dictionary by 45 degrees since N-ish is 315 to 45, E-ish 45 to 135

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

DarrenWiens2 — Thu, 22 Sep 2016 20:11:21 GMT

Ahhh, yes that's right. Well, you get the idea.

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

BlakeTerhune — Thu, 22 Sep 2016 20:29:10 GMT

Yeah, I did the same thing

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

DanPatterson_Retired — Thu, 22 Sep 2016 20:31:44 GMT

making digtize so much cleaner, since you can slice the 0-360 range anyway you like and the angle 'fits' in its correct position

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

DanPatterson_Retired — Sat, 11 Dec 2021 17:39:26 GMT

rather than messing up the original script post.

Direction (one variant of many... wiki it for the others)

Cardinal Degree range
N 348.75 - 11.25
NNE 11.25 - 33.75
NE 33.75 - 56.25
ENE 56.25 - 78.75
E 78.75 - 101.25
ESE 101.25 - 123.75
SE 123.75 - 146.25
SSE 146.25 - 168.75
S 168.75 - 191.25
SSW 191.25 - 213.75
SW 213.75 - 236.25
WSW 236.25 - 258.75
W 258.75 - 281.25
WNW 281.25 - 303.75
NW 303.75 - 326.25
NNW 326.25 - 348.75

import numpy as np
global a
global c
a = np.arange(11.25, 360., 22.5)
c = np.array(['N', 'NNE', 'NE', 'ENE', 'E', 'ESE', 'SE', 'SSE', 
              'S', 'SSW', 'SW', 'WSW', 'W', 'WNW', 'NW', 'NNW', 'N'])
def compass(angle):
    """ test """
    return c[np.digitize([angle], a)]‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Expression for the field calculator

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

For general testing or for single entry use and testing.

angles = np.arange(0, 360, 20) #[0, 44, 46, 134, 136, 224, 226, 314, 316, 359]
    for i in angles:
        print("{} => {}".format(i, compass(i)))‍‍‍‍‍‍

Result

0 => ['N']
20 => ['NNE']
40 => ['NE']
60 => ['ENE']
80 => ['E']
100 => ['E']
120 => ['ESE']
140 => ['SE']
160 => ['SSE']
180 => ['S']
200 => ['SSW']
220 => ['SW']
240 => ['WSW']
260 => ['W']
280 => ['W']
300 => ['WNW']
320 => ['NW']
340 => ['NNW']
‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

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

bobcostanza — Fri, 23 Sep 2016 15:41:48 GMT

I don't know what are appropriate responses for this new forum but I want to thank you all for your help. I should be able to give the scripts a test on Monday. I do need to calculate NNE, SSW, WSW, etc.

It appears that the new forum is a collaborative effort between a bunch of people? I'll try to read about it.

I am really surprised that my question was new. I thought a half hour of Googling and I'd find how to do it.

Bob

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

DarrenWiens2 — Fri, 23 Sep 2016 16:21:20 GMT

It depends what you were searching for. Does it ever work to search for a ready-made script that does exactly what you want? You really just need a "Python if statement" (or more likely, several), which produces endless useful search results explaining how to do what you need to do, if you look at the more general problem.

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

bobcostanza — Thu, 29 Sep 2016 16:25:03 GMT

Dan, I just got around to working with the script you provided. Should your last expression from Sep 23, 2016 10:38 AM work as is except for my field name with the angles?

Thanks

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

DanPatterson_Retired — Thu, 29 Sep 2016 17:51:44 GMT

make a text field to put the result in.... the !YourFieldNameWiththeAnglesGoesInTheExpression!

goes between the double ! marks.

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

bobcostanza — Thu, 29 Sep 2016 23:13:09 GMT

Oh, crap. I think I made it a number field!

Thanks Dan, I'll try again on Monday.

Bob