blocks|key|3446426|text|这是我的尝试。这是我找到的最接近的了。我使用gcIntermediate()来计算美国地图的中心点和位于bbox之外的数据点之间的最短距离。因此，箭头位置可能不是您想要的位置。我希望其他人能在这次尝试的基础上提供更好的解决方案。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3446427|我首先用美国缩放地图中的中心点排列了你的df+(即te)。然后我选择了不在美国地图的bbox中的数据点。然后，添加两列以指示美国地图的中心点。重命名两列并使用gcIntermediate计算最短距离。|3446428|library(dplyr)
library(ggplot2)
library(geosphere)

filter(te,+!between(lng,+-128,+-114)+%7C+!between(lat,+30,+52))+%25>%25
mutate(start_long+=+(-128+-+114)+/+2,
+++++++start_lat+=+(30+%2B+52)+/+2)+%25>%25
rename(end_lat+=+lat,+end_long+=+lng)+%25>%25
do(fortify(as(gcIntermediate(.[,c("start_long",+"start_lat")],
+++++++++++++++++++++++++++++.[,c("end_long",+"end_lat")],
+++++++++++++++++++++++++++++100,
+++++++++++++++++++++++++++++breakAtDateLine+=+FALSE,
+++++++++++++++++++++++++++++addStartEnd+=+TRUE,
+++++++++++++++++++++++++++++sp+=+TRUE),+"SpatialLinesDataFrame")))+->+foo|code-block|syntax|javascript|3446429|foo包含100个数据点，用于绘制相应的直线。我选择了靠近bbox边界的数据点。我专门为每一行寻找两个数据点，以便以后可以使用geom_segment()。我承认我有点玩弄了过滤条件。最后，在这种情况下，我没有使用lat设置数据子集。|3446430|filter(foo,+between(long,+-128,+-126.5)+%7C+between(long,+-115.5,+-114))+%25>%25
group_by(group)+%25>%25
slice(c(1,n()))+->+mydf|3446431|在下一步中，我基于this+link对数据帧进行了重新排列|3446432|mutate(mydf,+end_long+=+lag(long),+end_lat+=+lag(lat))+%25>%25
slice(n())+->+mydf2|3446433|最后我用箭头画了一张地图。我希望这将为您提供某种基础。我也希望其他SO用户能提供更好的解决方案。|3446434|ggplot()+%2B
geom_polygon(data+=+all_states,+aes(x+=+long,+y+=+lat,+group+=+group),
+++++++++++++colour+=+"gray",+fill+=+"gray"+)+%2B
coord_cartesian(ylim+=+c(30,+52),+xlim+=+c(-128,-114))+%2B
geom_point(data+=+te,+aes(x+=+lng,y+=+lat),+color+=+"blue",+size+=+5,alpha+=+0.6)+%2B
geom_segment(data+=+mydf2,+aes(x+=+end_long,+xend+=+long,
+++++++++++++++++++++++++++++++y+=+end_lat,+yend+=+lat,+group+=+group),
+++++++++++++++++++++++++++++++arrow+=+arrow(length+=+unit(0.2,+"cm"),+ends+=+"last"))|3446435|​|3446436|📷|atomic|3446437|3446438|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/18747706/adding-a-bunch-of-arrows-to-a-ggmap|1|IMAGE|IMMUTABLE|imageUrl|https://ask.qcloudimg.com/http-save/yehe-900000/0a397b3c9d3b1bb7f8842f9074e254dc.png|imageAlt^0|M|G|0|0|0|0|3|1R|E|0|0|9|9|0|0|0|0|0|0|0|1|1|0|0^^$0|@$1|2|3|4|5|6|7|1I|8|@$9|1J|A|1K|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|1L|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|1M|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|1N|8|@$9|1O|A|1P|B|C]|$9|1Q|A|1R|B|C]]|D|@]|E|$]]|$1|O|3|P|5|J|7|1S|8|@]|D|@]|E|$K|L]]|$1|Q|3|R|5|6|7|1T|8|@]|D|@$9|1U|A|1V|1|1W]]|E|$]]|$1|S|3|T|5|J|7|1X|8|@]|D|@]|E|$K|L]]|$1|U|3|V|5|6|7|1Y|8|@]|D|@]|E|$]]|$1|W|3|X|5|J|7|1Z|8|@]|D|@]|E|$K|L]]|$1|Y|3|Z|5|6|7|20|8|@]|D|@]|E|$]]|$1|10|3|11|5|12|7|21|8|@]|D|@$9|22|A|23|1|24]]|E|$]]|$1|13|3|Z|5|6|7|25|8|@]|D|@]|E|$]]|$1|14|3|-4|5|6|7|26|8|@]|D|@]|E|$]]]|15|$16|$5|17|18|19|E|$1A|1B]]|1C|$5|1D|18|1E|E|$1F|1G|1H|-4]]]]

Here is my attempt. This is the closest I got. I used <code>gcIntermediate()</code> for calculating the shortest distance between the center point of your US map and the data points which stay outside of the bbox. Hence, the arrow positions may not be something you want. My hope is that somebody else would deliver a better solution based on this attempt.

I first arranged your df (i.e., te) with the center point in the US zoomed map. I then chose data points which are not in the bbox of the US map. Then, add two columns to indicate the center point of the US map. Rename two columns and calculate the shortest distance with gcIntermediate.

<pre><code>library(dplyr)
library(ggplot2)
library(geosphere)

filter(te, !between(lng, -128, -114) | !between(lat, 30, 52)) %&gt;%
mutate(start_long = (-128 - 114) / 2,
 start_lat = (30 + 52) / 2) %&gt;%
rename(end_lat = lat, end_long = lng) %&gt;%
do(fortify(as(gcIntermediate(.[,c("start_long", "start_lat")],
 .[,c("end_long", "end_lat")],
 100,
 breakAtDateLine = FALSE,
 addStartEnd = TRUE,
 sp = TRUE), "SpatialLinesDataFrame"))) -&gt; foo
</code></pre>

<code>foo</code> contains 100 data points to draw respective line. I chose data points which stay close to the bbox boundary. I was specifically looking for two data points for each line so that I could use <code>geom_segment()</code> later. I admit that I played with the filter condition a bit. In the end, I did not subset data using lat in this case.

<pre><code>filter(foo, between(long, -128, -126.5) | between(long, -115.5, -114)) %&gt;%
group_by(group) %&gt;%
slice(c(1,n())) -&gt; mydf
</code></pre>

In the next step, I rearranged the data frame based on <a href="https://stackoverflow.com/questions/18747706/adding-a-bunch-of-arrows-to-a-ggmap">this link</a>

<pre><code>mutate(mydf, end_long = lag(long), end_lat = lag(lat)) %&gt;%
slice(n()) -&gt; mydf2
</code></pre>

Finally I drew the map with arrows. I hope this will provide some kind of base for you. I also hope that other SO users will provide better solutions.

<pre><code>ggplot() +
geom_polygon(data = all_states, aes(x = long, y = lat, group = group),
 colour = "gray", fill = "gray" ) +
coord_cartesian(ylim = c(30, 52), xlim = c(-128,-114)) +
geom_point(data = te, aes(x = lng,y = lat), color = "blue", size = 5,alpha = 0.6) +
geom_segment(data = mydf2, aes(x = end_long, xend = long,
 y = end_lat, yend = lat, group = group),
 arrow = arrow(length = unit(0.2, "cm"), ends = "last"))
</code></pre>

<img src="https://i.stack.imgur.com/WRIwh.png" alt="enter image description here">

blocks|key|399946|text|这个解决方案使用sp和rgeos包来操作空间数据，主要的症结是相交的直线和一个长方体多边形来获得箭头的边缘点。然后，如果使用geom_segment和零宽度绘制箭头，则该线不可见，仅保留箭头头。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|399947|此函数用于计算线框交点：|399948|boxint+<-+function(xlim,+ylim,+xp,+yp){
++++##+build+box+as+SpatialPolygons
++++box+=+cbind(xlim[c(1,2,2,1,1)],
++++++++ylim[c(1,1,2,2,1)])
++++box+<-+sp::SpatialPolygons(list(sp::Polygons(list(sp::Polygon(box)),ID=1)))

++++##+get+centre+of+box
++++x0=mean(xlim)
++++y0=mean(ylim)

++++##+construct+line+segments+to+points
++++sl+=+sp::SpatialLines(
++++++++lapply(1:length(xp),
+++++++++++++++function(i){
+++++++++++++++++++sp::Lines(list(sp::Line(cbind(c(x0,xp[i]),c(y0,yp[i])))),ID=i)
+++++++++++++++}
+++++++++++++++)
++++++++)
++++##+intersect+lines+segments+with+boxes+to+make+points
++++pts+=+rgeos::gIntersection(sl,+as(box,+"SpatialLines"))
++++as.data.frame(sp::coordinates(pts),+row.names=1:length(xp))
}|code-block|syntax|javascript|399949|这将返回带箭头的geom：|399950|wherelse+<-+function(xlim,+ylim,+points){
++++##+get+points+outside+bounding+box
++++outsides+=+points[!(
++++++++points$lng>=xlim[1]+&
++++++++++++points$lng+<=+xlim[2]+&
++++++++++++++++points$lat+>=+ylim[1]+&
++++++++++++++++++++points$lat+<=+ylim[2]),]
++++npts+=+nrow(outsides)
++++##+get+centre+point+of+box
++++x+=+rep(mean(xlim),npts)
++++y+=+rep(mean(ylim),npts)

++++##+compute+box-point+intersections
++++pts+=+boxint(xlim,+ylim,+outsides$lng,+outsides$lat)
++++pts$x0=x
++++pts$y0=y
++++##+create+arrow+segments+as+invisible+lines+with+visible+arrowheads
++++ggplot2::geom_segment(data=pts,+aes(x=x0,y=y0,xend=x,yend=y),
+++++++lwd=0,+arrow=grid::arrow(length=unit(0.5,"cm"),
+++++++type="closed"),col="magenta")
}|399951|所以你的例子，基本的图是：|399952|sp+=+ggplot()+%2B+
++geom_polygon(
+++data=all_states,+
++++aes(x=long,+y=lat,+group+=+group),colour="gray",fill="gray"+)+%2B+
++++coord_cartesian(ylim=c(30,+52),+xlim=c(-128,-114))+%2B+
++++geom_point(data=te,aes(x=lng,y=lat),color="blue",size=5,alpha=0.6)|399953|然后使用以下命令添加箭头：|399954|sp+%2B+wherelse(c(-128,-114),+c(30,52),+te)|399955|​|399956|📷|atomic|399957|399958|不过，我不确定是否有像你想要的那样绘制箭头的选项！|399959|entityMap|0|IMAGE|mutability|IMMUTABLE|imageUrl|https://ask.qcloudimg.com/http-save/yehe-900000/3ae20d0f806bb2dec68148fdff8b852b.png|imageAlt^0|8|2|B|5|1Q|C|0|0|0|8|4|0|0|0|0|0|0|0|0|1|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1F|8|@$9|1G|A|1H|B|C]|$9|1I|A|1J|B|C]|$9|1K|A|1L|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|1M|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|1N|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|1O|8|@$9|1P|A|1Q|B|C]]|D|@]|E|$]]|$1|O|3|P|5|J|7|1R|8|@]|D|@]|E|$K|L]]|$1|Q|3|R|5|6|7|1S|8|@]|D|@]|E|$]]|$1|S|3|T|5|J|7|1T|8|@]|D|@]|E|$K|L]]|$1|U|3|V|5|6|7|1U|8|@]|D|@]|E|$]]|$1|W|3|X|5|J|7|1V|8|@]|D|@]|E|$K|L]]|$1|Y|3|Z|5|6|7|1W|8|@]|D|@]|E|$]]|$1|10|3|11|5|12|7|1X|8|@]|D|@$9|1Y|A|1Z|1|20]]|E|$]]|$1|13|3|Z|5|6|7|21|8|@]|D|@]|E|$]]|$1|14|3|15|5|6|7|22|8|@]|D|@]|E|$]]|$1|16|3|-4|5|6|7|23|8|@]|D|@]|E|$]]]|17|$18|$5|19|1A|1B|E|$1C|1D|1E|-4]]]]

This solution uses <code>sp</code> and <code>rgeos</code> packages to manipulate spatial data, the main crux being intersecting lines and a box polygon to get the edge points for arrows. Then if you draw arrows with <code>geom_segment</code> and zero width, the line is invisible and only the arrow head remains.

This function computes the line-box intersections:

<pre><code>boxint &lt;- function(xlim, ylim, xp, yp){
 ## build box as SpatialPolygons
 box = cbind(xlim[c(1,2,2,1,1)],
 ylim[c(1,1,2,2,1)])
 box &lt;- sp::SpatialPolygons(list(sp::Polygons(list(sp::Polygon(box)),ID=1)))

 ## get centre of box
 x0=mean(xlim)
 y0=mean(ylim)

 ## construct line segments to points
 sl = sp::SpatialLines(
 lapply(1:length(xp),
 function(i){
 sp::Lines(list(sp::Line(cbind(c(x0,xp[i]),c(y0,yp[i])))),ID=i)
 }
 )
 )
 ## intersect lines segments with boxes to make points
 pts = rgeos::gIntersection(sl, as(box, "SpatialLines"))
 as.data.frame(sp::coordinates(pts), row.names=1:length(xp))
}
</code></pre>

And this returns the <code>geom</code> with arrows:

<pre><code>wherelse &lt;- function(xlim, ylim, points){
 ## get points outside bounding box
 outsides = points[!(
 points$lng&gt;=xlim[1] &amp;
 points$lng &lt;= xlim[2] &amp;
 points$lat &gt;= ylim[1] &amp;
 points$lat &lt;= ylim[2]),]
 npts = nrow(outsides)
 ## get centre point of box
 x = rep(mean(xlim),npts)
 y = rep(mean(ylim),npts)

 ## compute box-point intersections
 pts = boxint(xlim, ylim, outsides$lng, outsides$lat)
 pts$x0=x
 pts$y0=y
 ## create arrow segments as invisible lines with visible arrowheads
 ggplot2::geom_segment(data=pts, aes(x=x0,y=y0,xend=x,yend=y),
 lwd=0, arrow=grid::arrow(length=unit(0.5,"cm"),
 type="closed"),col="magenta")
}
</code></pre>

So your example, the basic plot is:

<pre><code>sp = ggplot() + 
 geom_polygon(
 data=all_states, 
 aes(x=long, y=lat, group = group),colour="gray",fill="gray" ) + 
 coord_cartesian(ylim=c(30, 52), xlim=c(-128,-114)) + 
 geom_point(data=te,aes(x=lng,y=lat),color="blue",size=5,alpha=0.6)
</code></pre>

and then add the arrows with:

<pre><code>sp + wherelse(c(-128,-114), c(30,52), te)
</code></pre>

<img src="https://i.stack.imgur.com/l35Y3.png" alt="enter image description here">

Not sure if there's an option to draw arrows exactly like you want them though!

I am generating maps with world-scale data, and then zooming in to certain regions. On the zoomed-in view, I would like to show that there are other data points outside the bounding box, by putting arrowheads that point from the center of the box to where the data point is in the outside world. 

Note: I do not need it to be a "great circle" path, just XY vectors in Mercator projection, because I imagine this will be useful for "normal" plots as well.

As an example, here is the world map showing the extent of the data:

<img src="https://i.stack.imgur.com/xdV9c.png" alt="enter image description here">

And here is the zoomed in view, with magenta arrows manually added to show what I would like to generate.

<img src="https://i.stack.imgur.com/8frzf.png" alt="close-up">

Below is the code and data I am using to generate these two basic plots. What I need is a way to generate the arrowheads.

<pre><code>require(ggplot2)

te = structure(list(lat = c(33.7399, 32.8571, 50.2214, 36.96263, 33.5835, 
33.54557, 47.76147, 48, 59.40289, 35.93411, 32.87962, 38.3241, 
50.03844, 37.44, 50.07774, 50.26668, 36.5944), lng = c(-118.37608, 
-117.25746, -5.3865, -122.00809, -117.86159, -117.79805, -124.45055, 
-126, -146.35157, -122.931472, -117.25285, -123.07331, -5.26339, 
25.4, -5.709894, -3.86828, -121.96201)), .Names = c("lat", "lng"
), class = "data.frame", row.names = c(NA, -17L))

all_states = map_data("world")

# world version:
wp = ggplot() + 
 geom_polygon(data = all_states, aes(x = long, y = lat, group = group), colour = "gray",
 fill = "gray") +
 coord_cartesian(ylim = c(0, 80), xlim = c(-155, 45)) + 
 geom_point(data = te, aes(x = lng, y = lat), color = "blue", size = 5,alpha = 0.6)

print(wp)

#states plot
sp = ggplot() +
 geom_polygon(data = all_states, aes(x = long, y = lat, group = group), colour = "gray", fill = "gray") +
 coord_cartesian(ylim = c(30, 52), xlim = c(-128, -114)) + 
 geom_point(data = te, aes(x = lng, y = lat), color = "blue", size = 5, alpha = 0.6) 

print(sp)
</code></pre>

Plot points outside grid as arrows pointing to data with ggplot2 in R

我正在用世界范围的数据生成地图，然后放大到特定的区域。在放大的视图中，我想通过将箭头从框的中心指向外部世界中数据点的位置来显示边界框外还有其他数据点。注：我不需要它是一个“大圆”路径，只需要墨卡托投影中的XY向量，因为我想这对“正常”图也是有用的。作为示例，以下是显示数据范围的世界地图：​​这是放大的视图，手动添加了洋...

问使用R中的ggplot2将栅格外部的点绘制为指向数据的箭头
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