Framed legend for a combined ErrorListPlot and ListLinePlot

Question

I am struggling to add legends to a combined plot of ErrorListPlot and ListLinePlot.
Here is the code.
When I tried to add PlotLegends to the individuals plots before displaying them on the same plot using Show, it did not work as shown in the screenshot attached below. I also tried using Legended[Show[]] which did not work as well.

Needs["ErrorBarPlots`"];
p1 = ErrorListPlot[{{{0.424, 0.555}, 
     ErrorBar[0.02, 0.15]}, {{0.709, 1.06}, 
     ErrorBar[0.015, 0.15]}, {{0.775, 1.33}, 
     ErrorBar[0.015, 0.15]}, {{0.901, 1.48}, 
     ErrorBar[0.015, 0.15]}, {{1.09, 2.16}, 
     ErrorBar[0.015, 0.15]}, {{1.33, 2.51}, 
     ErrorBar[0.015, 0.15]}, {{1.37, 2.48}, 
     ErrorBar[0.015, 0.1]}, {{1.57, 2.69}, ErrorBar[0.015, 0.1]}},
   PlotStyle -> 
    Directive[Medium, PointSize[Medium], "LineOpacity" -> 0.6, 
     Darker[Blue]] ];

p2 = ListLinePlot[{{ [Pi]/2, 
     2.6130091136816382` }, {1.4707963267948965` , 
     2.571050976016374` }, {1.3707963267948966` , 
     2.451257910107298` }, {1.2707963267948965` , 
     2.268388904666741` }, {1.1707963267948966` , 
     2.0426280363757554` }, {1.0707963267948966` , 
     1.794600396342152` }, {0.9707963267948966` , 
     1.542145438269968` }, {0.8707963267948966` , 
     1.2988682339826867` }, {0.7707963267948966` , 
     1.0738556387461116` }, {0.6707963267948966` , 
     0.8726024301612353` }, {0.5707963267948967` , 
     0.697929615345146` }, {0.4707963267948967` , 
     0.5509379917002875` }, {0.3707963267948966` , 
     0.43163064824113223` }, {0.2707963267948965` , 
     0.3395489795879398` }, {0.17079632679489642` , 
     0.2741253483791365` }, {0.07079632679489634` , 
     0.23498065023767406` }}, InterpolationOrder -> 3, 
   PlotStyle -> Blue, PlotLegends -> "y"];

Show[p1, p2, PlotRange -> Automatic, AxesOrigin -> {0, 0}, 
 Frame -> True, 
 FrameLabel -> {"Rebounding velocity (m/s)", 
   "Contact angle [Theta]"}, 
 FrameStyle -> Directive[Black, FontSize -> 14], 
 LabelStyle -> {FontFamily -> "Helvetica"}]

Is there any way for me to add legends to the combined plot, one for the ErrorListPlot and another one for the ListLinePlot, and put the legends in a box inside the final combined graph? Thank you.

Alexei Boulbitch · Accepted Answer

Try this:
 Show[p1, p2, PlotRange -> Automatic, AxesOrigin -> {0, 0}, 
     Frame -> True, 
     FrameLabel -> {"Rebounding velocity (m/s)", 
       "Contact angle [Theta]"}, 
     FrameStyle -> Directive[Black, FontSize -> 14], 
     LabelStyle -> {FontFamily -> "Helvetica"},
(*Here starts the description of the custom-made legend *)
     Epilog -> 
      Inset[Panel[
        Grid[{{Graphics[{Blue, PointSize[0.3], Point[{0, 0}]}, 
            ImageSize -> {20, 20}], 
           Style["  Data", 
            14]}, {Graphics[{Blue, Thickness[0.1], 
             Line[{{-1, 0}, {1, 0}}]}, ImageSize -> {20, 20}], 
           Style["  Fitting", 14]}}, Alignment -> {Left, Center}, 
         Spacings -> 0], ImageSize -> {105, 80}], Scaled[{0.8, 0.25}]]
(*Here ends the description of the custom-made legend *)
     ]

with the following effect

It is not difficult to programmatically draw the error intervals in addition to the dot within the legend if needed.
Instead of Panel one can use here Framed as follows:
Show[p1, p2, PlotRange -> Automatic, AxesOrigin -> {0, 0}, 
 Frame -> True, 
 FrameLabel -> {"Rebounding velocity (m/s)", 
   "Contact angle [Theta]"}, 
 FrameStyle -> Directive[Black, FontSize -> 14], 
 LabelStyle -> {FontFamily -> "Helvetica"},
 (*Here starts the description of the custom-made legend*)
 Epilog -> 
  Inset[Framed[
    Grid[{{Graphics[{Blue, PointSize[0.3], Point[{0, 0}]}, 
        ImageSize -> {20, 20}], 
       Style["  Data", 
        14]}, {Graphics[{Blue, Thickness[0.1], 
         Line[{{-1, 0}, {1, 0}}]}, ImageSize -> {20, 20}], 
       Style["  Fitting", 14]}}, Alignment -> {Left, Center}, 
     Spacings -> 0], ImageSize -> {105, 80}, RoundingRadius -> 5], 
   Scaled[{0.8, 0.25}]]
 (*Here ends the description of the custom-made legend*)
 ]

yielding this

The advantage is the possibility to make rounded corners (if it is the advantage for you).
Have fun!

kglr · Answer

You can construct the desired legend using LineLegend
legend = LineLegend[{Darker @ Blue, Blue}, {"Data", "y"}, 
  Joined -> {False, True}, 
  LegendFunction -> 
     (Framed[#, RoundingRadius -> 5, FrameStyle -> Directive[Gray, Thin]] &)];

show = Show[p1, p2, 
  AxesOrigin -> {0, 0}, Frame -> True, 
  FrameLabel -> {"Rebounding velocity (m/s)", "Contact angle θ"}, 
  PlotRange -> Automatic, 
  FrameStyle -> Directive[Black, FontSize -> 14], 
  LabelStyle -> {FontFamily -> "Helvetica"}];

and use legend and show with Legended:
Legended[show, Placed[legend, {.8, .25}]]

To place legend interactively inside the plot frame, you can use LocatorPane with show as background and  legend as option setting for Apperance:
LocatorPane[{{1.25, .5}}, show, Appearance -> legend]

Note: With this approach you need to create p1and p2 without the option PlotLegends. By the way, you need to use PlotLegends -> {"y"} to get a legend in your second plot.

Framed legend for a combined ErrorListPlot and ListLinePlot

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