topic Re: arctan in field calculator in Spatial Data Science Questions

arctan in field calculator

aTomasaLooström — Fri, 31 Oct 2014 09:41:46 GMT

Hello!

I want to calculate the slope of the roof of the house and get the result in degrees. I have the height difference between the highest and lowest points of the roof and the length of the roof in the attribute table. Have tried math.atan () but do not get it to work. I have used field calculator.

Tomas

Re: arctan in field calculator

DanPatterson_Retired — Fri, 31 Oct 2014 10:54:47 GMT

show the field calculator expression... also, you do have the python parser selected? Did you go to the Results window and check the error message? and if so what was it?

Re: arctan in field calculator

aTomasaLooström — Fri, 31 Oct 2014 11:00:39 GMT

Hi,

Yes I have the python parser, the expression is:

math.atan(2.5/2.75 )

I get a result but it is wrong or not i degree. The result I get is 0,737815 it should be 42.

Re: arctan in field calculator

ArnoldKuilman — Fri, 31 Oct 2014 13:15:09 GMT

Result is in radians: 0.737815 / PI *180 = 42

Solution is to divide the atan output answer by PI, and multiply by 180.

Re: arctan in field calculator

DanPatterson_Retired — Fri, 31 Oct 2014 13:18:58 GMT

of course atan doesn't return degrees, it needs to be converted using the math.degree method

>>> import math

>>> math.degrees(math.atan(2.5/2.75))

42.27368900609374

>>>

Re: arctan in field calculator

aTomasaLooström — Mon, 03 Nov 2014 06:21:53 GMT

Hi,

Thanks a lot!

Re: arctan in field calculator

aTomasaLooström — Mon, 03 Nov 2014 06:22:36 GMT

Thanks a lot, my maths are quite old...