[R] Smooth contour of a map
Pierre Bruyer
pbruyer at agaetis.fr
Wed May 18 17:59:06 CEST 2011
It's perfect, thank you!
I would like post the final code if someone need help in this subject, but I try to correct
a last problem, how can I constrain the contourLines() function to take the corner points of the map in his result ... it does not consider this point like a contour point.
Le 18 mai 2011 à 15:18, David Winsemius a écrit :
> You may be looking for the par settings of xaxs="i", yaxs="i", which if you add them to the plot call will prevent the "regular" behavior of adding 4% padding to the axis widths.
>
> ?par
>
> -- David.
>
> On May 18, 2011, at 8:27 AM, Pierre Bruyer wrote:
>
>> 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)$y ,col = colgraph[tmp+1], border = NA)
>> }
>>
>>
>>
>> Le 17 mai 2011 à 16:44, Pierre Bruyer a écrit :
>>
>>> The result is good, thanks a lot, but how can I with this method fill my raster to color?
>>>
>>> Le 17 mai 2011 à 15:43, Duncan Murdoch a écrit :
>>>
>>>> I don't think filled.contour gives you access to the contour lines. If you use contourLines() to compute them, then you can draw them using code like this:
>>>>
>>>> contours <- contourLines(V2b,levels=paliers)
>>>> for (i in seq_along(contours)) {
>>>> x <- contours[[i]]$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
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
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>> and provide commented, minimal, self-contained, reproducible code.
>
> David Winsemius, MD
> Heritage Laboratories
> West Hartford, CT
>
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