# [STATSGRASS] RE: [GRASS-user] kriging

Alexandre Leroux alexandre.leroux at ec.gc.ca
Mon Sep 25 14:54:18 EDT 2006

```Hi Maris,

Using interpolation breaklines (in the actual discussion, 'faults') does
not provide the same results as patching two partly-masked
interpolations. Do no forget breaklines can be non-strait complex
curves, that's why is does not give you the same results as using masks.

Say you have:
xxxxx
xxoxx
xxoxx
x1o2x
ooooo

where o = land, your breakline, and x = water. 1 and 2 are two 'x' water
points. When masking land 'o' and interpolating, 1 and 2 will influence
each side of the land arm (the 'o' land that goes north) while they
shouldn't since there is land between them. I do not know the exact
algorythm, but this can't happen when using breaklines. I hope this
example I was clear enough to convince you the result of masks and
breaklines is not the same... :-)

Cheers,

Alex

Māris Nartišs wrote:
> Hi Maciek,
>
> I will disagree with You - as
> http://surfit.sourceforge.net/surfit/fault__approx_8tcl-example.html says:
> "The main idea of fault curves is that parts of resulting surface between
> fault curve are independent of each other."
> It's like masking areas between fault lines, interpolating them seperatly and
> patching together. Only difference - in GRASS you must do it manualy for each
> fault-enclosed area.
>
> Maris.
>
> On Monday 25 September 2006 15:35, Maciej Sieczka wrote:
>> Markus,
>>
>> That's not the same. I don't you can achieve this:
>>
>> http://surfit.sourceforge.net/surfit/fault_8tcl-example.html
>> http://surfit.sourceforge.net/surfit/fault__approx_8tcl-example.html
>>
>> using Grass. In Grass you can't use lines as interpolation faults. The
>> method you refer to uses area masking, and it can't reproduce the
>> Surfit examples.
>>
>> Maciek
--
Alexandre Leroux, M.Sc., Ing.