topic Re: Exp function to get antilog in Geoprocessing Questions

Exp function to get antilog

MichaelAugust — Thu, 09 Oct 2014 17:50:27 GMT

I am trying to take some result values and log transform them with the field calculator, then krig them to a surface - I found this in the help regarding the log function:

"field calculator uses the natural Log not Log10(x)

try;

Log ( [Area] ) / Log ( 10 )"

I did that and it seemed to work, but how do I calculate the antilog or exp back correctly of the surface, I can't seem to get back to values that correlate to my original data (which ranges from 0.00001 to 0.003047) - I run:

Exp("log_krig")

in the raster calculator and end up with values of 0.00252001 to 0.0755711...I'm wondering if there's a reverse of the above trick to get the antilog of my surface somehow (i.e. get back from Log transformed data to original)? My mathematics are not strong...thanks for any help!

Re: Exp function to get antilog

DanPatterson_Retired — Thu, 09 Oct 2014 20:08:26 GMT

Natural log Ln This example calculates the natural logarithm (base e) of the input raster values

Exp This example calculates the base e exponential of the input raster values,

Is this the pairing you are looking for? there is Log10, Ln, Log2 and Exp10, Exp, Exp2

Re: Exp function to get antilog

MichaelAugust — Thu, 09 Oct 2014 20:27:51 GMT

Wow, somehow I just did not see the exp10 in the raster calculator list the first time - thanks Dan!

Re: Exp function to get antilog

DanPatterson_Retired — Thu, 09 Oct 2014 20:46:06 GMT

No problem...the terms differ depending upon which software you are using...wait until you get into python...