[GRASS-user] log(0)-error in r.mapcalculator

[Patrick S.]

Thank you so much, Markus!

That was the missing hint and it works now!
However, I just went through the documentation, which says: "/F/ means 
that the functions always results in a floating point value" and 
Function "log" has "F".

This is somehow misleading and rather should be an "*". Can I correct 
that somewhere without access-rights (to contribute) or would I rather 
report this?


Patrick






  that On 11/08/2012 07:34 PM, Markus Metz wrote:
> On Thu, Nov 8, 2012 at 10:50 AM, Patrick S. <patrick_GIS at gmx.ch> wrote:
>> Dear List,
>>
>> I keep getting a log(0) error in r.mapcalculator, even if I enlarge the
>> data. This seems to be a bug as I controlled the same data with R and get
>> (non-infinity) values. Does r.mapcalculator eventually truncate the results
>> of formulas to some integer values?
>>
>> logit-expression:  log(((A/100)/(1-(A/100)))
> In r.mapcalc, the numbers are treated as integers. Try instead log(((A
> / 100.0) / (1.0 - (A / 100.0)))
> Changing e.g. 1 to 1.0 forces r.mapcalc to do floating point calculations.
>
> HTH,
>
> Markus M
>
>
>> To avoid error of log(0) I enlarged the data by 0.00001, 1 and 5 but keep
>> getting the error.
>>
>> I run it out of R with:
>> param<-list(amap="r_slope_perc", formula="log(((A+0.00001)/100)/(1-(A/100)))
>> ", outfile="r_slope_perc_logit")
>> execGRASS("r.mapcalculator", parameters=param, flags=c("overwrite"))
>>
>> (r.mapcalculator amap="r_slope_perc",
>> formula="log(((A+0.00001)/100)/(1-(A/100)))" outfile="r_slope_perc_logit"
>> --overwrite)
>>
>>
>> Any ideas why this happens?
>>
>> Patrick
>> _______________________________________________
>> grass-user mailing list
>> grass-user at lists.osgeo.org
>> http://lists.osgeo.org/mailman/listinfo/grass-user

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