[R] Smooth contour of a map

[Duncan Murdoch]

I don't think filled.contour gives you access to the contour lines.  If 
you use contourLines() to compute them, then you can draw them using 
code like this:

  contours <- contourLines(V2b,levels=paliers)
  for (i in seq_along(contours)) {
    x <- contours[[i]]$x
    y <- contours[[i]]$y
    lines( splines( seq_along(x), x)$y, splines( seq_along(y), y)$y )
}

but as I said, you won't get great results.  A better way is to use a 
finer grid, e.g. by fitting a smooth surface to your set of points and 
using predictions from the model to interpolate.

Duncan Murdoch


On 17/05/2011 9:35 AM, Pierre Bruyer wrote:
> I work with large datasets (10000 points) so I can't post them , but my function is :
>
> create_map<- function(grd, level ,map_output, format = c("jpeg"), width_map = 150, height_map = 150,...)
> {	
> 		
> 	##sp<- spline(x = grd[,1], y = grd[,2])
>
> 	grd2<- matrix(grd[,3], nrow = sqrt(length(grd[,3])), ncol = sqrt(length(grd[,3])), byrow = FALSE)
> 	
> 	V2b<- grd2
>
> 	
> 	##creation of breaks for colors
> 	i<-1	
> 	paliers<- c(-1.0E300)
> 	while(i<=length(level[,1]))
> 	{
> 		paliers<- c(paliers,level[i,1])
> 		i<- i+1
> 	}
> 	paliers<- c(paliers, 1.0E300)
> 		
> 	##scale color creation
> 	i<- 1
> 	colgraph<- c(rgb(255,255,255, maxColorValue = 255))
> 	while(i<=length(level[,2]))
> 	{
> 		colgraph<- c(colgraph, rgb(level[i,2],level[i,3],level[i,4], maxColorValue = 255))
> 		i<- i +1
> 	}
>
> 	##user can choose the output format (default is jpeg)
> 	switch(format,
> 		png = png(map_output, width = width_map, height = height_map) ,
> 		jpeg = jpeg(map_output, width = width_map, height = height_map, quality = 100),
> 		bmp = bmp(map_output, width = width_map, height = height_map),
> 		tiff = tiff(map_output, width = width_map, height = height_map),
> 		jpeg(map_output, width = width_map, height = height_map))
>
> 	## drawing map
> 	
> 	##delete marge
> 	par(mar=c(0,0,0,0))
> 	filled.contour(V2b, col = colgraph, levels = paliers, asp = 1, axes = FALSE, ann = FALSE)
> 	dev.off() 		
>
> }
>
> where grd is a xyz data frame,
> map_output is the path+name of the output image file,
> and level is a matrix like this :
>
>
> level<- matrix(0,10,4)
> level[1,1]<- 1.0000E+00
> level[2,1]<- 3.0000E+00
> level[3,1]<- 5.0000E+00
> level[4,1]<- 1.0000E+01
> level[5,1]<- 1.5000E+01
> level[6,1]<- 2.0000E+01
> level[7,1]<- 3.0000E+01
> level[8,1]<- 4.0000E+01
> level[9,1]<- 5.0000E+01
> level[10,1]<- 7.5000E+01
>
>
> level[1,2]<- 102
> level[2,2]<- 102
> level[3,2]<- 102
> level[4,2]<- 93
> level[5,2]<- 204
> level[6,2]<- 248
> level[7,2]<- 241
> level[8,2]<- 239
> level[9,2]<- 224
> level[10,2]<- 153
>
> level[1,3]<- 153
> level[2,3]<- 204
> level[3,3]<- 204
> level[4,3]<- 241
> level[5,3]<- 255
> level[6,3]<- 243
> level[7,3]<- 189
> level[8,3]<- 126
> level[9,3]<- 14
> level[10,3]<- 0
>
> level[1,4]<- 153
> level[2,4]<- 204
> level[3,4]<- 153
> level[4,4]<- 107
> level[5,4]<- 102
> level[6,4]<- 33
> level[7,4]<- 59
> level[8,4]<- 63
> level[9,4]<- 14
> level[10,4]<- 51
>
> Le 17 mai 2011 à 15:17, Duncan Murdoch a écrit :
>
> >  On 17/05/2011 8:24 AM, Pierre Bruyer wrote:
> >>  Thank you for your answer, but the function spline() (and a lot of other function in R)  can't take in its parameters the original contour which are define by a vector, i.e. :
> >>
> >
> >  If you post some reproducible code to generate the contours, someone will show you how to use splines to interpolate them.
> >
> >  Duncan Murdoch
> >
> >>  	##creation of breaks for colors
> >>  	i<-1	
> >>  	paliers<- c(-1.0E300)
> >>  	while(i<=length(level[,1]))
> >>  	{
> >>  		paliers<- c(paliers,level[i,1])
> >>  		i<- i+1
> >>  	}
> >>  	paliers<- c(paliers, 1.0E300)
> >>
> >>
> >>
> >>  Le 17 mai 2011 à 13:05, Duncan Murdoch a écrit :
> >>
> >>  >   On 11-05-17 5:58 AM, Pierre Bruyer wrote:
> >>  >>   I'm a French developer (so I am sorry if my english is not perfect). I have a problem to smooth the contours of a map. I have a dataset with 3 columns, x, y and z, where x and y are the coordinates of my points and z is evaluate to a qualitative elevation and his representation is a set of colors, which is define by levels.
> >>  >>
> >>  >>   The problem is the curve of my contour is so linear, and I would like a more continuous contour. I use the function fitted.contour to draw my map.
> >>  >
> >>  >   If you use a finer grid of x,y values you'll get shorter segments and they will look smoother.
> >>  >
> >>  >   You might be able to use a smooth interpolator (e.g. spline()) rather than linear interpolation, but those occasionally do strange things e.g.
> >>  >
> >>  >   x<- c(1:4, 5.9, 6:10)
> >>  >   y<- c(1:4,   7, 6:10)
> >>  >   plot(spline(x,y, n=200), type="l")
> >>  >   points(x,y)
> >>  >
> >>  >   where one point is out of line with the others, but the curve overcompensates in order to stay smooth.
> >>  >
> >>  >   Duncan Murdoch
> >>
> >
>