s.surf.tps - handling islands

[Anantha Prasad]

Hi Helena,

As you are aware I used your s.surf.tps to get population density
maps for Insular SE Asia...The problem is that since there are 
so many islands, the interpolation treats the oceans as an inter-
polating surface. Hence we have high population values for 
Kalimantan (which actually has low pop.den but has very few points)
because the neighbouring hi-pop.den Java is spreading the high values
over the ocean, into Kalimantan. 
 I need your advice on this:
1. Is there a way I can tell s.surf.tps (maybe a new version) not 
to interpolate over oceans (ie., have bounds for interpolation).
2. If this is not possible,I was thinking of introducing some dummy
points with v. low pop.den values in the oceans and interpolating -
which can be quite laborious.
3. Do you suggest using hi-tension values with smoothing to 
restrict the spreading of the high popden values...(I had used a 
tension of 600 without smoothing - but the results were NOT 
satisfactory).

Please let me have your input. Thanks a lot. 

Anantha Prasad
Ph: 244-2166