points_approx.tcl

This example shows how one goes from randomly spaced data points to an evenly sampled surface. We have 13504 approximation points (file examples/surfit/points/points.txt) and equidistant grid with more than 250000 nodes. To approximate points to evenly sampled smooth surface we do the following things:

• load scattered points to the memory
• create equidistant grid of 512x512 nodes
• set some additional parameters (tolerance, map_name)
• create sequence of gridding rules (how to use data points and space between them)
• run Description of the surfit gridding algorithm algorithm
• save results to file

See also:

points, points_add, completer

Here is the image of the resulting surface:

Pic 1. approximation surface

Pic 2. small part of approximation surface

This result was obtained with "examples/surfit/points/points_approx.tcl" script.

Some comments to script:

• map_name variable is used to set name of resulting surface
• tol variable is used to manage tolerance of iterative linear system solver algorithm. If this value is too big, an iterative algorithm will make low number of iterations and it will lead to rough result.
• grid_unload function call to remove grid grid from result file.
• to produce more smoother surface you should reduce weight value in points_add command. To produce more precise approximation (surface tends to interpolation) you should enlarge weight value in points_add command.

#
# This script was generated with funner v2.1beta (www.gridding.info)

# 
# load plugins
# 
load libsurfit[info sharedlibextension]

# remove all previous data and gridding rules
clear_data 

# set name of surface
set map_name "map_points_approx" 

# set tolerance for cg solver
set tol 1e-006 

##
## load initial data 
##
 
# load points from text file 
pnts_read "points.txt" "points"  
 
##
## construct grid 
##
grid 150 150 
 
##
## create gridding rules
##

# resulting surface should tend to be constant or plane 
completer 1 2  

# add "resulting surface at points = points values" with weight 
points_add 0.6 "points" 

##
## run gridding algorithm
##
surfit 

##
## save results 
##

# unload grid from memory
grid_unload 

# save surface to surfit datafile 
surf_save "points_approx.dat" "map_points_approx" 

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surfit: open source gridding and contouring software.