CODEWITHSUNDEEP
rlinesequencepolygonsegment
Nick
Nick

Reputation: 1106

How to split line segments by a line equation?

I have a four segments on the plane defined by coordinats:

A <- matrix(c(0, 4, 4, 0, 0,            # x    
              0, 0, 3, 3, 0), ncol=2)   # y

x <- A[,1]
y <- A[,2]
n <- dim(x)

xx <- c()
yy <- c()

The segment's lengths are great 1. I heed to split all segments with step equals 1.

My attempt is below. I have computed the length of i-th segment, dist, and now working with a horizontal segment only. I should add new values of x-coordinats then repeat dist-1 times y-coordinat.

for (i in 1:n-1){
dist <- sqrt((x[i] - x[i+1])^2 + (y[i] - y[i+1])^2)
if (!is.null(dist) & length(dist) > 0 & dist[1] > 1)
    {   
        # horizontal segment, 'y' is const
        if (y[i] - y[i+1] == 0)
        {    
            # split a horizontal segment on (dist-1) parts with step 1

            tmp <- c(seq(from = min(x[i], x[i+1]),
                            to   = max(x[i], x[i+1])))

            # remove 1st and last elements
            xx <- c(xx, tmp[2 : (length(tmp)-1)]) 
            yy <- c(yy, rep(y[i], dist-1));
         } # if
    } #if
#} # i
xx;yy;

Output is: 

> x
[1] 1 2 3 1 2 3
> y
[1] 0 0 0 3 3 3

C <- matrix(c(x,y), ncol=2)

plot(A, col='red', type= 'l', xlim=c(min(A[,1]),max(A[,1])),
      ylim=c(min(A[,2]),max(A[,2])), xlab='x', ylab='y'); 
points(A, col='black', pch = 22); 

points(C, col='red', pch = 21); 
grid()

seq

Question. How to split segments by equation of a line from 2 points?

https://algs4.cs.princeton.edu/91primitives/

Upvotes: 0

Views: 172

Answers (1)

R&#233;mi Coulaud
R&#233;mi Coulaud

Reputation: 1714

I'm sorry but my understanding of what you clearly want is not perfect. But maybe it is to find all the equation or trace all segments between 2 points from the above exemple ? If I use segments function in R to trace 10 * 10 segments, is it what you want ?

all_points <- unique(rbind(A, C))

indices <- expand.grid(1:10, 1:10)
plot(all_points, xlim = c(0, 4), ylim = c(0, 3), xlab = "X", ylab = "Y")
for(i in 1:10){
  segments(x0 = all_points[indices[i, 1], 1],
           y0 = all_points[indices[i, 1], 2],
           x1 = all_points[indices[i, 2], 1],
           y1 = all_points[indices[i, 2], 2]
           )
}

enter image description here

Upvotes: 1

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