[GRASSLIST:5182] Regarding interpolation

Abhay Kulkarni abhayak_anr at sancharnet.in
Sat Dec 7 23:43:34 EST 2002

Hi all !!

I am a new grassuser,totally new to GIS and working on grass5.0.0pre2_i686 on 
my RH Linux 7.1. Basically I am a computer profession but interested a lot in 

I digitized a contour map of the scale 1 cm = 30 mtrs. (1:3000) in x-y 
projection. (image size 3500 x 2550 pixels , 300dpi). I wanted to visualize 
it in 3D. The modules r.thin,r.line,r.contour could not help as (probably ) 
there was a lot of text and other markings on the scanned image. So I 
digitized the map manually using v.digit and attributed the lines.

When I ran the module v.surf.rst, it gave the message " taking too long to 
find points for interpolation - please change the region to area where your 
points are. Continuing calculations... ". Before I understand its meaning, 
the system hanged. This happened twice.

Then I ran v.support and then v.to.rast. Then I used r.surf.idw2, created the 
elevation map and viewed it in nviz. I got a wonderful 3D view. That matched 
the contour lines but shape was not smooth (like elevation.dem in the 
spearfish). It was like polygons of sharp edges stacked on each other.

Will anybody please guide me where I was wrong ? It took some 2 and a half 
hours for r.surf.idw2 on my 128 MB (plus 256 Swap) PC for 1256 rows. Is this 
a normal time ?

Thanking you.

Abhay Kulkarni,

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