C Library Functions - contourlines (3)
NAME
contourlines(3f) - [M_contourplot] calculate contour lines from ungridded data f(x,y) and call user-supplied routine with results
CONTENTS
Synopsis
Description
Authors
Comments
Options
Example
SYNOPSIS
SUBROUTINE ContourLines(x,y,z,ismopt,iexp,jexp,clist,epsilon,ierr,cntcrv)
real,intent(in),dimension(:) :: x real,intent(in),dimension(:) :: y real,intent(in),dimension(:) :: z integer,intent(in) :: ismopt integer,intent(in) :: iexp integer,intent(in) :: jexp real,intent(in),dimension(:) :: clist real,intent(out) :: epsilon integer,intent(out) :: ierr external cntcrv
DESCRIPTION
contourlines(3f) is a general algorithm for the construction of contour plots. It computes contour lines of constant z for the function z = f(x,y).
From the original COSMIC description:
The graphical presentation of experimentally or theoretically generated data sets frequently involves the construction of contour plots. A general computer algorithm has been developed for the construction of contour plots. The algorithm provides for efficient and accurate contouring with a modular approach which allows flexibility in modifying the algorithm for special applications. The algorithm accepts as input data values at a set of points irregularly distributed over a plane. The algorithm is based on an interpolation scheme in which the points in the plane are connected by straight line segments to form a set of triangles. In general, the data is smoothed using a least-squares-error fit of the data to a bivariate polynomial. To construct the contours, interpolation along the edges of the triangles is performed, using the bivariable polynomial if data smoothing was performed. Once the contour points have been located, the contour may be drawn.
AUTHORS
This is a public domain routine from PDAS (Public Domain Aeronautical Software) converted to modules; which was derived from COSMIC Program Number ARC-11441; which originated at NASA Ames Research Center, circa 1981.
COMMENTS
From the original PDAS description:
There are many additional algorithms available for computation of contour lines. There are several in the Transactions for Mathematical Software and elsewhere. This routine was deemed worthy of inclusion in the NASA COSMIC collection, but I cannot swear to its status among contour generators.
OPTIONS
x input list of x values y input list of y values z input list of z values ismopt smoothing option flag (0=no/off, 1=yes/on) iexp,jexp i and j exponent value for smoothing If smoothing is used, these values are used to define a polynomial used for a least-squares fit of the data. clist list of constant contour values epsilon error function (normalized value) returned to caller if ismopt is non-zero ierr return error flag
0. for normal return 1. for invalid value for number of values in x,y,z 2. for number of ismopt coefficients greater than ’maxcof’ or number of values in x,y,z
EXAMPLE
TEST1:
! program demo_contourlines and user routine program TestCase use M_ContourPlot, only : contourlines implicit none ! integer,parameter :: NPTS=121 real,parameter,dimension(8):: c = & [0.1, 0.2, 0.5, 1.0, 2.0, 4.0, 6.0, 8.0] real :: eps integer :: errCode integer,parameter :: DBG=2 integer :: ierr !integer :: iexp=0, jexp=0, ism=0 integer :: iexp=2, jexp=3, ism=1 integer :: i,j,k real,dimension(NPTS) :: x,y,z external :: my_CntCrv ! k=0 do j=0,10 do i=0,10 k=k+1 x(k)=0.1*real(i) y(k)=0.1*real(j) end do end do ! z=(x-0.5)**2 + (y-0.5)**2 z(:)=16.0*z(:) ! ! write out the input values for inspection open(unit=dbg, file=’test.log’, status=’replace’, & & iostat=errCode, action=’write’, position=’rewind’) write(DBG,’(I4,3F12.6)’) (k,x(k),y(k),z(k),k=1,npts) ! call ContourLines(x,y,z, ism,iexp,jexp, c, eps,ierr,my_CntCrv) END PROGRAM TestCase ! ---------------------------------------------------------------- subroutine my_CntCrv(x,y,n,z) ! User-supplied routine used to plot or process the contour lines implicit none integer,intent(in) :: n real,intent(in),dimension(n):: x,y real,intent(in) :: z ! integer,save :: gnu=0 integer :: k integer :: errCode if(gnu.eq.0)then ! on first call, set up output file gnu=1 open(unit=gnu, file=’test1.gnu’, status=’replace’, & & iostat=errCode, action=’write’, position=’rewind’) write(*,*) "File test1.gnu added to your directory" endif ! write a contour line out to a file followed by a blank line write(gnu,’("# level ",g0)’) z write(gnu,’(2f12.5)’) (x(k),y(k),k=1,n) write(gnu,’(a)’) " " ! end subroutine my_CntCrv ! end program demo_contourlines and user routine#!/bin/sh # Example execution of gnuplot(1) to plot the output file gnuplot <<\EOF plot ’test1.gnu’ with lines pause mouse "click mouse to exit ..." quit
EOF
| Nemo Release 3.1 | contourlines (3) | February 23, 2025 |
