Smooth contour of a map

I've pratically resolved my problem (the code is under that), but a  
last thing is not perfect:
when I use the function plot to call after the function polygon,  
there is a marge between my raster and the window. I think it's the  
axis of the function "plot()", but I have not found how delete it.  
Someone have a solution please?

Pierre Bruyer

##smooth contour
	
	contours <- contourLines(V2b,levels=paliers)

	
	par(mar=c(0,0,0,0))
	plot(1,col="white",main="polygon()", asp = 1, axes = FALSE, ann =  
FALSE,xlim=c(0,1), ylim = c(0,1),type = "n", method = c("image"))
	for (i in seq_along(contours)) {
		 x <- contours[[i]]$x
		 y <- contours[[i]]$y
		 c <- contours[[i]]$level
		 j <- 1
		 tmp <- 0
		 while(j < length(level[,1]) && tmp == 0){
		 	if(level[j,1] == c){
		 		tmp <- j
		 	}
		 	j <- j+1
		}	

		polygon( spline( seq_along(x), x)$y, spline( seq_along(y), y) 
$y ,col = colgraph[tmp+1], border = NA)
	}



Le 17 mai 2011 ? 16:44, Pierre Bruyer a ?crit :

The result is good, thanks a lot, but how can I with this method  
fill my raster to color?

Le 17 mai 2011 ? 15:43, Duncan Murdoch a ?crit :

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 ? 15:17, Duncan Murdoch a ?crit :

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 ? 13:05, Duncan Murdoch a ?crit :

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