Labeling vertices of a polygon in Mathematica - wolfram-mathematica

Question

Given a set of points in the plane T={a1,a2,...,an} then Graphics[Polygon[T]] will plot the polygon generated by the points. How can I add labels to the polygon's vertices? Have merely the index as a label would be better then nothing. Any ideas?

Answer 1

pts = {{1, 0}, {0, Sqrt[3]}, {-1, 0}};
Graphics[
{{LightGray, Polygon[pts]},
{pts /. {x_, y_} :> Text[Style[{x, y}, Red], {x, y}]}}
]
To add point also
pts = {{1, 0}, {0, Sqrt[3]}, {-1, 0}};
Graphics[
{{LightGray, Polygon[pts]},
{pts /. {x_, y_} :> Text[Style[{x, y}, Red], {x, y}, {0, -1}]},
{pts /. {x_, y_} :> {Blue, PointSize[0.02], Point[{x, y}]}}
}
]
update:
Use the index:
pts = {{1, 0}, {0, Sqrt[3]}, {-1, 0}};
Graphics[
{{LightGray, Polygon[pts]},
{pts /. {x_, y_} :>
Text[Style[Position[pts, {x, y}], Red], {x, y}, {0, -1}]}
}
]

Answer 2

Nasser's version (update) uses pattern matching. This one uses functional programming. MapIndexed gives you both the coordinates and their index without the need for Position to find it.
pts = {{1, 0}, {0, Sqrt[3]}, {-1, 0}};
Graphics[
{
{LightGray, Polygon[pts]},
MapIndexed[Text[Style[#2[[1]], Red], #1, {0, -1}] &, pts]
}
]
or, if you don't like MapIndexed, here's a version with Apply (at level 1, infix notation ###).
pts = {{1, 0}, {0, Sqrt[3]}, {-1, 0}};
idx = Range[Length[pts]];
Graphics[
{
{LightGray, Polygon[pts]},
Text[Style[#2, Red], #1, {0, -1}] & ### ({pts, idx}\[Transpose])
}
]
This can be expanded to arbitrary labels as follows:
pts = {{1, 0}, {0, Sqrt[3]}, {-1, 0}};
idx = {"One", "Two", "Three"};
Graphics[
{
{LightGray, Polygon[pts]},
Text[Style[#2, Red], #1, {0, -1}] & ### ({pts, idx}\[Transpose])
}
]

Answer 3

You can leverage the options of GraphPlot for this. Example:
c = RandomReal[1, {3, 2}]
g = GraphPlot[c, VertexLabeling -> True, VertexCoordinateRules -> c];
Graphics[{Polygon#c, g[[1]]}]
This way you can also make use of VertexLabeling -> Tooltip, or VertexRenderingFunction if you want to. If you do not want the edges overlaid, you may add EdgeRenderingFunction -> None to the GraphPlot function. Example:
c = RandomReal[1, {3, 2}]
g = GraphPlot[c, VertexLabeling -> All, VertexCoordinateRules -> c,
EdgeRenderingFunction -> None,
VertexRenderingFunction -> ({White, EdgeForm[Black], Disk[#, .02],
Black, Text[#2, #1]} &)];
Graphics[{Brown, Polygon#c, g[[1]]}]