[R-sig-Geo] Distmap Inconsistency?

[Agustin Lobo]

Dear list,

I have 2 raster (im) objects (ai and escenai) which
are identical except by 1 single pixel
at position 356,777:

 > ai$v[356,777]
[1] 255
 > escenai$v[356,777]
[1] NA

I calculate distmap for both:

refdist <- distmap(as.owin(ai))
adist630 <- distmap(as.owin(escenai))

As the only difference is that ai$v has a filled cell
at position 356,777, and distmap calculates distances to the
nearest not NA cell, values of adist630 should be either
equal or higher than refdist values. Nevertheless, this is not
the case for few cells:

dif <- (refdist$v - adist630$v)
 > range(dif)
[1] -25.01976  30.44687
 > dif[dif>0]
  [1]  6.638003 30.446868 29.122913 27.613710 25.879159 23.867316 
21.509986 18.716394
  [9] 15.364044 11.285587  6.250307

Is this a problem with distmap or am I misunderstanding something?
I can send the rda file upon request if anybody can help.

Agus

-- 
Dr. Agustin Lobo
Institut de Ciencies de la Terra "Jaume Almera" (CSIC)
LLuis Sole Sabaris s/n
08028 Barcelona
Spain
Tel. 34 934095410
Fax. 34 934110012
email: Agustin.Lobo at ija.csic.es
http://www.ija.csic.es/gt/obster