Python code for straight line slope of a polyline (inc. straight line length, pecentage slope, and degrees slope)

[#1]

Follow these instructions to calculate the percentage and degrees slope for any polyline layer with z values.

1. Add fields to the attribute table for: a) straight line length; b) percentage slope; c) degrees slope.

2. Use the Field Calculator to compute the straight line length using this Python code. NB - if your polylines are straight, then you can omit this step and instead calculate the Length field using 'Calculate Geometry' as normal.

Code block:

import math
def GetDistance(shape):
  distance = math.sqrt((math.pow(shape.firstpoint.x - shape.lastpoint.x, 2)) + (math.pow(shape.firstpoint.y - shape.lastpoint.y, 2)))
  return distance

3. Use the Field Calculator to compute the percentage slope using this Python code. NB - if you have straight polylines then you can subsitute the normal 'Length' field for the straight line length (called Straight_L in this example).

Code block:

import math
def GetSlopePerc(shape, leng):
  ratio = (math.fabs(shape.lastpoint.z - shape.firstpoint.z))/ leng
  percentage = ratio * 100
  return percentage

4. Use the Field Calculator to compute the percentage slope using this Python code. Note that Slope_pcen is the percentage slope field.

Code block:

import math
def GetSlopeDeg(shape, percentage):
  ratio = percentage / 100
  radians = math.atan(ratio)
  degrees = radians * (180/math.pi)
  return degrees

Alternatively, you can return the slope in degrees using this maths module function:

math.degrees()

(Thanks to Neil Ayres for suggesting this alteration)

Hopefully this has been helpful! Let me know if these codes through any errors for you.

[NeilAyres]

And the math module has functions

math.radians()

math.degrees()

[CamillaRootes]

Thanks for suggesting this. I'd not thought to put the code block in syntax format but it definitely improves the document.