Plot region from given coordinates

Question

How can I connect given coordinates and create figure from it? Can I fill it with colour? I tried:

Line[{a[[1]], a[[2]], a[[3]], a[[4]], a[[5]], a[[1]]}]

where a is my list. It doesnt look good.

a consists of coordinates in 2D {x,y} pairs. I want to connect all points to form a region/space/figure and fill that region with colour.

We need more information. Provide an example list a. What do you mean by "fill it with color"? - the line has a color? - color fill between the line and the axis? What do you mean by "it doesn't look good"? Did you embed the Line in a Graphics object? Etc. — march, Dec 17 '15 at 19:45
a consists of coordinates {{-0.9504, -0.31103}, {-0.946885, -0.321572}, {0.848087, 0.529857}, {0.998268, -0.0588254}}
I want to connect them to form a region/space/figure and fill that region with colour. — Tsin, Dec 17 '15 at 19:48
Please add relevant information to your post by clicking the grey edit button at the bottom of the post. In addition, please format your code correctly. — march, Dec 17 '15 at 19:50
it doesnt always works. For some values sometimes it creates figures like this http://i.imgur.com/tAeOCSa.png?1
I want it to create geometric figures — Tsin, Dec 17 '15 at 20:16
Either re-order the points so that it works or possibly you can use ConvexHullMesh@a. — march, Dec 17 '15 at 20:28
I am using random points for my list a, so it needs to work for any combination. ConvexHull seems to do the job :) but can I change the colour? thx — Tsin, Dec 17 '15 at 20:42
See also How to ensure that Polygon[list] plots a simple polygon? and Rebuild a polygon so it doesn't self intersect — , Dec 17 '15 at 21:38
Found the solution by combining new commands I found in google. The answer is:
Graphics[Line[{a[[Last[FindShortestTour[a]]]]}]] — Tsin, Dec 17 '15 at 21:53

score 3 · Answer 1 · edited Jan 17 '16 at 16:17

3

Just for fun

(*psuedo-data*)
data = RandomReal[{0, 10}, {5, 2}];

(*process*)
Manipulate[
  Graphics[{col, Polygon @ pts}],
  {{pts, data}, Locator},
  {{col, Green, "Color"}, {Green, Blue, Red}}]

edited Jan 17 '16 at 16:17

m_goldberg

107,779
16
103
257

answered Jan 17 '16 at 01:43

e.doroskevic

5,959
1
13
32

Omg 1k reputation! – e.doroskevic Jan 17 '16 at 16:03

David G. Stork · Answer 2 · 2015-12-18T00:47:53.820

1

To avoid polygons whose edges cross themselves, try this:

ConvexHullMesh[a]

For instance:

a = RandomReal[{0, 1}, {5, 2}];

Graphics[Polygon[a]]

ConvexHullMesh[a]

or

ConvexHullMesh[a, PlotTheme -> "Lines", MeshCellStyle -> Black]

Note that FindShortestTour does not work:

a = {{0, 0}, {1, 0}, {1, .1}, {2, .1}, {2, 0}, {3, 0}, {1.5, 1}};

Graphics[Line[a[[FindShortestTour[a][[2]]]]]]

which is not convex.

edited Dec 18 '15 at 00:47

answered Dec 18 '15 at 00:31

David G. Stork

41,180
3
34
96

1

Why is it a problem if the FindShortestTour solution is not convex? – Dec 18 '15 at 01:22
There is no reason the shortest tour need be convex... The shortest tour must go through every point, which includes those in the interior of the convex hull. Hence the shortest tour will rarely be convex. – David G. Stork Dec 18 '15 at 01:25
Yes, that's fine, but why is that a problem? You say this approach "does not work", but the asker didn't ask for a convex figure. – Dec 18 '15 at 01:28
Yes he did... when he wrote: "it doesn't always work. For some values sometimes it creates figures like this i.imgur.com/tAeOCSa.png?1 I want it to create geometric figures." – David G. Stork Dec 18 '15 at 01:29
@David that's self intersection, but non convex is probably fine. – LLlAMnYP Jan 17 '16 at 01:26

Plot region from given coordinates

2 Answers2