220 lines
11 KiB
Markdown
220 lines
11 KiB
Markdown
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### How To Draw A Sinus?
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In data visualization tasks, quite often there is a need to depict mathematical
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functions - for example, to compare the convergence rate of a model
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with ideal one or to find an approximation for a given time series. Such charts
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have a number of features that are not inherent in most other charts: for example,
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visualizing the perpendicular axes (OX, OY) from (0, 0) and a large number of
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additional information. This can be the expected value of the function, its extremum
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points, deviation at various points, etc.
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This article will tell you how to depict an ordinary sinus using the library `Plotly.kt`
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so that in the end you will get a visual and informative plot.
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1. Let's start with drawing perpendicular OX and OY axes. This requires to do a few things:
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hide default axes lines, hide zero lines (it's impossible to draw an arrow on the end of it),
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add perpendicular arrows using annotations (`Text`) with visible arrows on the end, but without
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text. After that, let's sign the axes themselves. It is also important to specify the required
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chart sizes (`width`,` height`) so that after saving the graph will look the same as in the browser.
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```kotlin
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Plotly.page { // making new html page with plot
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layout {
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width = 900 // width of the plot (in px.)
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height = 500 // height of the plot (in px.)
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text { // vertical axis
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x = Value.of(0) // position of the top end of the arrow = (0, 1+eps)
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y = Value.of(1 + eps)
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ax = Value.of(0) // ax, ay means the offset of the bottom edge relative to the top
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ay = Value.of(430) // positive (negative) value is the arrow length
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// upwards (top down) and from right to left (from left to right)
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}
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text { // horizontal axis
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y = Value.of(0) // arrow left position = (2PI + eps, 0)
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x = Value.of(2 * PI + eps)
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ax = Value.of(-800) // position of the left end of the arrow
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ay = Value.of(0)
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}
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xaxis { // OX parameters
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showline = false // hide OX line
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zeroline = false // hide zero line
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}
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yaxis { // OY parameters
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showline = false // hide OY line
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zeroline = false // hide zero line
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}
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}
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}.makeFile() // making temporary file and visualing plot in the browser
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```
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2. Now we will draw the sinus function itself - for its visualization let's choose a bright blue color,
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contrasting with both the white background and the black ticks on the axes. After that using
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the variation of the `mode` parameter (` ScatterMode: lines, markers`) the intersection points with the OY axis
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will be marked with a slightly darker shade of the same color.
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```kotlin
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x1 = (-410..410).map{ it / 200 * PI } // function domain (-2PI - eps, 2PI + eps)
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y1 = sin(x1) // function values
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Plotly.page {
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scatter { // making Scatter plot (sinus)
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x.set(x1) // assigning OX values
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y.set(y1) // assigning OY values
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line { color(XKCD.CERULEAN) } // color of the line is cerulean
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}
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scatter { // making Scatter plot (OX axis dots)
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mode = ScatterMode.markers // visualizing only dots
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x(-2* PI, -PI, PI, 2* PI) // points of intersection of sinus with OX (values along the X axis)
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y(0, 0, 0, 0) // points of intersection of sinus with OX (values along the Y axis)
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line { color(XKCD.CERULEAN_BLUE) } // color of the dots is darker cerulean
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marker { size = 8 } // dot's diameter is 8 px.
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}
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layout { ... }
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}.makeFile()
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```
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3. Let's draw horizontal dashed lines on the chart, corresponding to values equal to -1, 1 (extremum lines) and 1/2.
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This requires changing `line.dash` parameter to `Dash.dash` value. The specified values will be plotted after that
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on the OY axis using the `tickvals` and` ticklabels` parameters.
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```kotlin
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...
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Plotly.page {
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...
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layout {
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shape { // adding new figure (line y = 1)
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x0 = Value.of(-2*PI) // (-2PI, 1) and (2PI, 1) coordinates
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x1 = Value.of(2*PI) // will be connected by a line
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y0 = Value.of(1)
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y1 = Value.of(1)
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line { dash = Dash.dash } // dashed type of the line
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}
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shape { // adding new figure (line y = 1/2)
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x0 = Value.of(-2*PI) // coordinates (-2PI, 1/2) and (2PI, 1/2)
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x1 = Value.of(2*PI) // will be connected by a line
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y0 = Value.of(0.5)
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y1 = Value.of(0.5)
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line {
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color("red") // red color of the line
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dash = Dash.dash // dashed type of the line
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}
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}
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shape { // adding new figure (line y = -1)
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x0 = Value.of(-2*PI) // coordinates (-2PI, -1) and (2PI, -1)
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x1 = Value.of(2*PI) // will be connected by a line
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y0 = Value.of(-1)
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y1 = Value.of(-1)
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line { dash = Dash.dash } // dashed type of the line
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}
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...
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}
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}.makeFile()
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```
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4. After that, it is worth adding vertical lines connecting points on OX, the values in
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which equals 1/2, and the value itself in LaTeX format. Shapes are used again for this - an array
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values of type `Shape.line`. To use LaTeX format you need to include the `MathJax` header.
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```kotlin
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...
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val sub = PI / 6
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val xElems = listOf(-2PI + sub, -PI - sub, 0 + sub, PI - sub)
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// points, where sinus equals 1/2
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val shapesList = mutableListOf<Shape>() // making list of lines
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for (x: xElems) {
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val shape = Shape {
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x0 = Value.of(x) // (x, 0) and (x, 0.5) will be connected
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y0 = Value.of(0)
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x1 = Value.of(x)
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y0 = Value.of(1/2)
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line { color("red") } // red color of the line
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}
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shapesList.add(shape) // adding new figure to the list
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}
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Plotly.page(mathJaxHeader, cdnPlotlyHeader) {
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scatter { // add string "1/2"
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mode = ScatterMode.text // visualing only text
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x(-0.35) // text position on the OX axis
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y(0.56) // text position on the OX axis
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text = listOf("$\Large{1/2}$") // increasing font size with ТеХ
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textfont { color("red") } // red color of the font
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showlegend = false // do not show this trace in the legend
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hoverinfo = "none" // do not show anything on hover
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}
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...
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layout { // adding figure list to the plot
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shapes = shapesList
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...
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}
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}.makeFile()
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```
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5. It remains to add labels on OX corresponding to the intersections of the sinus with the axis. It
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is done in a similar way, using axis labels (`tickvals`,` ticktext`) and writing text in LaTeX format.
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```kotlin
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...
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Plolty.page(mathJaxHeader, cdnPlotlyHeader) {
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...
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layout {
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xaxis { // OX axis parameters
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...
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anchor = "free" // axis position is set manually
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position = 0.43 // assigning axis position
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tickvals(listOf(-2 * PI-0.05, -PI - 0.15, PI - 0.05, 2 * PI + 0.1))
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ticktext(listOf("\$\\huge{-2\\pi}\$", "\$\\huge{-\\pi}\$", "\$\\huge{\\pi}\$", "\$\\huge{2\\pi}\$"))
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// ticks positions and text
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}
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yaxis { // OY axis parameters
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...
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anchor = "free" // axis position is set manually
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position = 0.485 // assigning axis position
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tickvals(listOf(-0.91, 0.09, 1.09))
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ticktext(listOf("\$\\Large{-1}\$", "\$\\Large{0}\$", "\$\\Large{1}\$"))
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// ticks positions and text
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}
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...
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}
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}.makeFile()
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```
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6. As a final improvement, let's add a legend to the plot, which will be placed in upper right corner of the graph.
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First you need to set the name of the corresponding line, after which with using the parameters `xanchor = right`
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and` yanchor = top` set the position of the legend so that the coordinates specified by the parameters
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`x = 1`,` y = 1` correspond to the position in the upper right corner of the image.
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```kotlin
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...
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Plotly.page(mathJaxHeader, cdnPlotlyHeader) {
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scatter { // sinus Scatter trace
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...
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name = "\$\\Large{y = \\mathrm{sin}\\,x}\$"
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// the name of the plot displayed in the legend
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}
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layout {
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legend { // legend parameters
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x = 0.97 // horizontal position of the legend
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y = 1 // vertical position of the legend
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borderwidth = 1 // width of the legend border
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font { size = 32 } // size of the legend font
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xanchor = XAnchor.right // "anchoring" the position of the legend to the right corner
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yanchor = YAnchor.top // "anchoring" the position of the legend to the bottom of the graph
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}
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...
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}
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}.makeFile()
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```
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7. Final picture:
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Source code is available at: https://github.com/mipt-npm/plotly.kt/tree/dev/examples/src/main/kotlin/tutorials/SinusPicture.kt
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