[GRASS-user] Slope categories from DEM ?

[Emma]

Dear all,

Thanks a lot for your answers. I tried the following:
----------------
1.
r.slope.aspect elevation=new_dem slope=new_slope format=degrees

2.
r.reclass input=new_slope output=new_slope_30 rules=grassrule.txt

where grassrule.txt contained:
1 thru 30 = 1
31 thru 90 = 2
----------------
This works pretty well and the result corresponds to what I wanted.  
Great !!

Now I also tried to use r.mapcalc instead of r.reclass as follows:
r.mapcalc 'new_slope_30_bis = if(new_slope > 30, 1, 0)'

However for some reason the resulting map new_slope_30_bis has:
Rows:         20
Columns:      20
Total Cells:  400

while the original new_slope, as well as new_slope_30 have both Total  
Cells:  47212692. So you can imagine the result is not very nice...

Why is this happening ? (and am I allowed to attach screenshots to my  
emails in this mailing list??)

Sincerely yours,
Emma


On 6-Nov-10, at 10:08 PM, Rich Shepard wrote:

> On Sat, 6 Nov 2010, Daniel Victoria wrote:
>
>> So, by reversing the test in the if statement will give you values  
>> of 1
>> for low slope areas.
>
>  In the question asked to start this thread, there's apparently no  
> interest
> in values == 30%. By default, those are included in the false  
> category. And
> if one wants them included in the true category the test condition  
> needs to
> be <= rather than just <.
>
> Rich
>
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