I wanted to draw 2 equilateral triangles. One upside down and the other upside up.
Here is my code:
ord<-c(1,3,5)
ord1<-c(2,4,6)
x1<-x[ord]
y1<-y[ord]
x2<-x[ord1]
y2<-y[ord1]
lines(x1,y1,col="blue")
lines(x2,y2,col="blue")
However, I can't get the figure to make complete triangle. I only get 2 sides of each triangle. What am I doing wrong?
lines will draw from the first coord to the second, second to third, etc. If you want it to come back to the first point, just duplicate it at the end:
ord <- c(1,3,5,1)
ord1 <- c(2,4,6,2)
to get it come back to the first point.
Using the fact that the third point is halfway between the first and the second, and the angle is pi/3, you can do this for example:
angle=pi/3
x <- c(0,0.5,0.5*cos(angle),0)
y <- c(0,0,sin(angle),0)
y1 <- c(0,0,-sin(angle),0)
plot(-1:1,-1:1,type='n')
polygon(x=x,y=y,col='red') ## you can replace polygon by lines here
polygon(x=x,y=y1,col='green')
Related
I have a large rivernetwork as a SpatialLines(DataFrame) and want to subset it so I get a SpatialLine with only the shortest/fastest path between two SpatialPoints(DataFrame) which propably need to be snapped onto the line first.
In the example Code, I want to get the closest line between the red dots, while moving on the lines. Also I want to move between the left red point and the right blue point, which needs to be snapped to the closest SpatialLine
library(sp)
x <- c(1,5,6,8)
y1 <- c(1,3,4,7)
y2 <- c(5,5,5,2)
L <- SpatialLines(list(Lines(Line(cbind(x,y1)), ID="a"),Lines(Line(cbind(x,y2)), ID="b")))
P <- SpatialPoints(data.frame(x=c(1,8),y=c(1,2)))
P_snap <- SpatialPoints(data.frame(x=c(8),y=c(1)))
plot(L)
points(P,col="red")
points(P_snap,col="blue")
I am trying to generate a plot which uses arrows as markers in Gnuplot. These arrows I want to turn in a specific angle which I know. So I have value triples of x1 ... xn, y1...yn, alpha1...alphan. Sorry, I wasn't able to include a pic from my hard drive to illustrate what I want to achieve.
Basically, for every (15th or so) x-y pair, the marker should be an arrow which uses a certain angle.
The measured data is tightly packed so I suppose I will have to define an increment between the markers. The length of the arrow can be the same all over.
I would appreciate your ideas.
Gnuplot has a plot mode with vectors that is what you want
Given that your file has the following format, x y angle and assuming that
your angle is in radians, you have to take into account that
with vectors requires 4 parameters, namely x y dx dy where dx
and dy are the projections of the lenght of the arrow.
this draws only the arrows, if you want a line you have to make
two passes on the data.
you want to draw an arrow for a data point over, say, 10 points.
That said, I'd proceed like this
dx(a) = 0.2*cos(a) # 0.2 is an arbitrary scaling factor
dy(a) = 0.2*sin(a)
# this draws the arrows
plot 'mydata.dat' every 10 using 1:2:(dx(a)):(dy(a)) with vectors
# this draws the line
plot 'mydata.dat'
You may want to use help plot to find the detailed explanation of all the parameters that you can apply to a with vectors plot.
Credits: An article on the gnuplotting site
I am having difficulty of producing X,Y coordinates of a circle and then drawing line segments to it. Basically what I want to do is draw 360 lines from the center of a circle to the outside of the circle in perfect spacing. This is how I am currently doing it but it is not working. If there is a different way to do this, that works great as well! Also I am hoping that degree 0 starts at the left side of the circle.
t <- seq(0,2*pi,length=360)
coords <- t(rbind( sin(t)*127.28125, cos(t)*127.28125))
plot(coords,type='n',xlim=c(-63.625625,63.625625),ylim=c(0,127.28125))
lines(coords)
deg=data.frame(coords[,1],coords[,2])
head(deg)
deg$count=1
deg$degree=1
for(i in 1:nrow(coords)){
if(deg$count[i]<=270){
deg$degree[i]=i-1+90-45
} else {
deg$degree[i]=i-1-270-45
}
}
names(deg)[1] <- "X"
names(deg)[2] <- "Y"
i=1
for(i in 1:19){
segments(0,0,deg$X[deg$degree==((5*(i-1)))],deg$Y[deg$degree==((5*(i-1)))])
cat(((5*(i-1))),'\t')
}
Update:
I am having some issues with where the lines get drawn. Basically as we go around the circle the errors get larger so when pi/2 radians happens and it is straight up, the value is slightly to the right of x=0. This may not be possible to get but thought I would ask to see if there was anyway to fix that! The 45 90 and 135 should all match on the lines.
How about this
th <- seq(0, 2*pi, length.out=360)
r <- 2
x <- r*cos(th)
y <- r*sin(th)
plot(x,y, type="n")
segments(0,0,x,y)
Basically i choose th and r in polar space and convert to Cartesian.
If you want to start with 0 on the left, use
x <- -r*cos(th)
instead.
I am stuck in simple problem. I have a scatter plot.
I am plotted confidence lines around it using my a custom formula. Now, i just want only the names outside the cutoff lines to be displayed nothing inside. But, I can't figure out how to subset my data on the based of the line co-ordinates.
The line is plotted using the lines function which is a vector of 128 x and y values. Now, how do I subset my data (x,y points) based on these 2 values. I can apply a static limit of a single number of sub-setting data like 1,2 or 3 but how to use a vector to subset data, got me stuck.
For an reproducible example, consider :
df=data.frame(x=seq(2,16,by=2),y=seq(2,16,by=2),lab=paste("label",seq(2,16,by=2),sep=''))
plot(df[,1],df[,2])
# adding lines
lines(seq(1,15),seq(15,1),lwd=1, lty=2)
# adding labels
text(df[,1],df[,2],labels=df[,3],pos=3,col="red",cex=0.75)
Now, I need just the labels, which are outside or intersecting the line.
What I was trying to subset my dataframe with the values used for the lines, but I cant make it right.
Now, static sub-setting can be done for single values like
df[which(df[,1]>8 & df[,2]>8),] but how to do it for whole list.
I also tried sapply, to cycle over all the values of x and y used for lines on the df iteratively, but most values become +ve for a limit but false for other values.
Thanks
I will speak about your initial volcano-type-graph problem and not the made up one because they are totally different.
So I really thought this a lot and I believe I reached a solid conclusion. There are two options:
1. You know the equations of the lines, which would be really easy to work with.
2. You do not know the equation of the lines which means we need to work with an approximation.
Some geometry:
The function shows the equation of a line. For a given pair of coordinates (x, y), if y > the right hand side of the equation when you pass x in, then the point is above the line else below the line. The same concept stands if you have a curve (as in your case).
If you have the equations then it is easy to do the above in my code below and you are set. If not you need to make an approximation to the curve. To do that you will need the following code:
df=data.frame(x=seq(2,16,by=2),y=seq(2,16,by=2),lab=paste("label",seq(2,16,by=2),sep=''))
make_vector <- function(df) {
lab <- vector()
for (i in 1:nrow(df)) {
this_row <- df[i,] #this will contain the three elements per row
if ( (this_row[1] < max(line1x) & this_row[2] > max(line1y) & this_row[2] < a + b*this_row[1])
|
(this_row[1] > min(line2x) & this_row[2] > max(line2y) & this_row[2] > a + b*this_row[1]) ) {
lab[i] <- this_row[3]
} else {
lab[i] <- <NA>
}
}
return(lab)
}
#this_row[1] = your x
#this_row[2] = your y
#this_row[3] = your label
df$labels <- make_vector(df)
plot(df[,1],df[,2])
# adding lines
lines(seq(1,15),seq(15,1),lwd=1, lty=2)
# adding labels
text(df[,1],df[,2],labels=df[,4],pos=3,col="red",cex=0.75)
The important bit is the function. Imagine that you have df as you created it with x,y and labs. You also will have a vector with the x,y coordinates for line1 and x,y coordinates for line2.
Let's see the condition of line1 only (the same exists for line 2 which is implemented on the code above):
this_row[1] < max(line1x) & this_row[2] > max(line1y) & this_row[2] < a + b*this_row[1]
#translates to:
#this_row[1] < max(line1x) = your x needs to be less than the max x (vertical line in graph below
#this_row[2] > max(line1y) = your y needs to be greater than the max y (horizontal line in graph below
#this_row[2] < a + b*this_row[1] = your y needs to be less than the right hand side of the equation (to have a point above i.e. left of the line)
#check below what the line is
This will make something like the below graph (this is a bit horrible and also magnified but it is just a reference. Visualize it approximating your lines):
The above code would pick all the points in the area above the triangle and within the y=1 and x=1 lines.
Finally the equation:
Having 2 points' coordinates you can figure out a line's equation solving a system of two equations and 2 parameters a and b. (y = a +bx by replacing y,x for each point)
The 2 points to pick are the two points closest to the tangent of the first line (line1). Chose those arbitrarily according to your data. The closest to the tangent the better. Just plot the spots and eyeball.
Having done all the above you have your points with your labels (approximately at least).
And that is the only thing you can do!
Long talk but hope it helps.
P.S. I haven't tested the code because I have no data.
I apologize in advance if my code looks very amateurish.
I'm trying to assign quadrants to 4 measurement stations approximately located on the edges of a town.
I have the coordinates of these 4 stations:
a <- c(13.2975,52.6556)
b <- c(14.0083,52.5583)
c <- c(13.3722,52.3997)
d <- c(12.7417,52.6917)
Now my idea was to create lines connecting the north-south and east-west stations:
line.1 <- matrix(c(d[1],b[1],d[2],b[2]),ncol=2)
line.2 <- matrix(c(a[1],c[1],a[2],c[2]),ncol=2)
Plotting all the stations the connecting lines looks allright, however not very helpful for analyzing it on a computer.
So I calculated the eucledian vectors for the two lines:
vec.1 <- as.vector(c((b[1]-d[1]),(b[2]-d[2])))
vec.2 <- as.vector(c((c[1]-a[1]),(c[2]-a[2])))
which allowed me to calculate the angle between the two lines in degrees:
alpha <- acos((vec.1%*%vec.2) / (sqrt(vec.1[1]^2+vec.1[2]^2)*
sqrt(vec.2[1]^2+vec.2[2]^2)))) * 180/pi
The angle I get for alpha is 67.7146°. This looks fairly good. From this angle I can easily calculate the other 3 angles of the intersection, however I need values relative to the grid so I can assign values from 0°-360° for the wind directions.
Now my next planned step was to find the point where the two lines intersect, add a horizontal and vertical abline through that point and then calculate the angle relative to the grid. However I can't find a proper example that does that and I don't think I have a nice linear equation system I could solve.
Is my code way off? Or maybe anyone knows of a package which could help me? It feels like my whole approach is a bit wrong.
Okay I managed to calculate the intersection point, using line equations. Here is how.
The basic equation for two points is like this:
y - y_1 = (y_2-y_1/x_2-x_1) * (x-x_1)
If you make one for each of the two lines, you can just substitute the fractions.
k.1 <- ((c[2]-a[2])/(c[1]-a[1]))
k.2 <- ((b[2]-d[2])/(b[1]-d[1]))
Reshaping the two functions you get a final form for y:
y <- (((-k.1/k.2)*d[2]+k.1*d[1]-k.1*c[1]+d[2])/(1-k.1/k.2))
This one you can now use to calculate the x-value:
x <- ((y-d[2])+d[1]*k.2)/k.2
In my case I get
y = 52.62319
x = 13.3922
I'm starting to really enjoy this program!
Wikipedia has a good article on finding the intersection between two line segments with an explicit formula. However, you don't need to know the point of intersection to calculate the angle to the grid (or axes of coordinate system.) Just compute the angles from your vec.1 and vec.2 to the basis vectors:
e1 <- c(1, 0)
e2 <- c(0, 1)
as you have done.