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Commit 9f0e5a7

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jklymakjklymak
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DOC: add infor to transforms tutorial about fig.dpi_scale_trans
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‎tutorials/advanced/transforms_tutorial.py

Copy file name to clipboardExpand all lines: tutorials/advanced/transforms_tutorial.py
+78-36Lines changed: 78 additions & 36 deletions
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@@ -18,38 +18,45 @@
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``ax`` is a :class:`~matplotlib.axes.Axes` instance, and ``fig`` is a
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:class:`~matplotlib.figure.Figure` instance.
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+-----------+-----------------------------+-----------------------------------+
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|Coordinates|Transformation object |Description |
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+-----------+-----------------------------+-----------------------------------+
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|"data" |``ax.transData`` |The coordinate system for the data,|
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| | |controlled by xlim and ylim. |
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+-----------+-----------------------------+-----------------------------------+
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|"axes" |``ax.transAxes`` |The coordinate system of the |
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| | |`~matplotlib.axes.Axes`; (0, 0) |
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| | |is bottom left of the axes, and |
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| | |(1, 1) is top right of the axes. |
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+-----------+-----------------------------+-----------------------------------+
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|"figure" |``fig.transFigure`` |The coordinate system of the |
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| | |`.Figure`; (0, 0) is bottom left |
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| | |of the figure, and (1, 1) is top |
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| | |right of the figure. |
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+-----------+-----------------------------+-----------------------------------+
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|"display" |``None``, or |The pixel coordinate system of the |
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| |``IdentityTransform()`` |display; (0, 0) is bottom left of |
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| | |the display, and (width, height) is|
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| | |top right of the display in pixels.|
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+-----------+-----------------------------+-----------------------------------+
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|"xaxis", |``ax.get_xaxis_transform()``,|Blended coordinate systems; use |
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|"yaxis" |``ax.get_yaxis_transform()`` |data coordinates on one of the axis|
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| | |and axes coordinates on the other. |
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+-----------+-----------------------------+-----------------------------------+
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+----------------+-----------------------------+-----------------------------------+
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|Coordinates |Transformation object |Description |
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+----------------+-----------------------------+-----------------------------------+
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|"data" |``ax.transData`` |The coordinate system for the data,|
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| | |controlled by xlim and ylim. |
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+----------------+-----------------------------+-----------------------------------+
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|"axes" |``ax.transAxes`` |The coordinate system of the |
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| | |`~matplotlib.axes.Axes`; (0, 0) |
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| | |is bottom left of the axes, and |
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| | |(1, 1) is top right of the axes. |
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+----------------+-----------------------------+-----------------------------------+
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|"figure" |``fig.transFigure`` |The coordinate system of the |
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| | |`.Figure`; (0, 0) is bottom left |
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| | |of the figure, and (1, 1) is top |
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| | |right of the figure. |
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+----------------+-----------------------------+-----------------------------------+
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|"figure-inches" |``fig.dpi_scale_trans`` |The coordinate system of the |
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| | |`.Figure` in inches; (0, 0) is |
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| | |bottom left of the figure, and |
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| | |(width, height) is the top right |
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| | |of the figure ininches. |
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+----------------+-----------------------------+-----------------------------------+
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|"display" |``None``, or |The pixel coordinate system of the |
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| |``IdentityTransform()`` |display window; (0, 0) is bottom |
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| | |left of the window, and (width, |
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| | |height) is top right of the |
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| | |display window in pixels. |
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+----------------+-----------------------------+-----------------------------------+
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|"xaxis", |``ax.get_xaxis_transform()``,|Blended coordinate systems; use |
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|"yaxis" |``ax.get_yaxis_transform()`` |data coordinates on one of the axis|
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| | |and axes coordinates on the other. |
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+----------------+-----------------------------+-----------------------------------+
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All of the transformation objects in the table above take inputs in
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their coordinate system, and transform the input to the `display`
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coordinate system. That is why the `display` coordinate system has
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`None` for the `Transformation Object` column -- it already is in
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their coordinate system, and transform the input to the ``display``
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coordinate system. That is why the ``display`` coordinate system has
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``None`` for the ``Transformation Object`` column -- it already is in
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display coordinates. The transformations also know how to invert
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themselves, to go from `display` back to the native coordinate system.
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themselves, to go from ``display`` back to the native coordinate system.
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This is particularly useful when processing events from the user
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interface, which typically occur in display space, and you want to
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know where the mouse click or key-press occurred in your data
@@ -71,6 +78,7 @@
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import numpy as np
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import matplotlib.pyplot as plt
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import matplotlib.patches as mpatches
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x = np.arange(0, 10, 0.005)
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y = np.exp(-x/2.) * np.sin(2*np.pi*x)
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# move, but the circle will remain fixed because it is not in `data`
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# coordinates and will always remain at the center of the axes.
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import matplotlib.patches as patches
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fig = plt.figure()
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ax = fig.add_subplot(111)
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x, y = 10*np.random.rand(2, 1000)
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ax.plot(x, y, 'go') # plot some data in data coordinates
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circ = patches.Circle((0.5, 0.5), 0.25, transform=ax.transAxes,
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circ = mpatches.Circle((0.5, 0.5), 0.25, transform=ax.transAxes,
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facecolor='yellow', alpha=0.5)
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ax.add_patch(circ)
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plt.show()
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# highlight the 1..2 stddev region with a span.
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# We want x to be in data coordinates and y to
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# span from 0..1 in axes coords
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rect = patches.Rectangle((1, 0), width=1, height=1,
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rect = mpatches.Rectangle((1, 0), width=1, height=1,
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transform=trans, color='yellow',
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alpha=0.5)
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#
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# trans = ax.get_xaxis_transform()
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#
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# .. _transforms-fig-scale-dpi:
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#
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# Plotting in physical units
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# ==========================
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#
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# Sometimes we want an object to be a certain physical size on the plot, in
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# which case the ``fig.dpi_scale_trans`` should be used. The following
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# example draws a circle displaced one inch from the bottom-left corner that
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# is 0.5-inches in diameter. Note that if you run this code with an
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# interactive window and resize, the circle stays in the same spot.
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fig, ax = plt.subplots(figsize=(3, 3))
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r = mpatches.Circle((1, 1), 1., transform=fig.dpi_scale_trans)
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fig.artists.append(r)
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plt.show()
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###############################################################################
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# Another use is putting a circle around a data point that is a certain size.
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# Though in this case if the figure is resized the circle doesn't follow the
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# data point. This is a good example of using ``inverted``:
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fig, ax = plt.subplots()
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xdata, ydata = (0.2, 0.7), (0.5, 0.5)
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ax.plot(xdata, ydata, "o")
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ax.set_xlim((0, 1))
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# get the coordinates of the data point in inches from lower left corner:
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x, y = fig.dpi_scale_trans.inverted().transform(
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ax.transData.transform((xdata[0], ydata[0])))
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# plot a circle around the point that is 50 points in diameter...
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circle = mpatches.Circle((x, y), 50/72, fill=None,
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transform=fig.dpi_scale_trans)
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# add to figure
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fig.artists.append(circle)
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plt.show()
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###############################################################################
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# .. _offset-transforms-shadow:
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#
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# Using offset transforms to create a shadow effect
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#
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# where `xt` and `yt` are the translation offsets, and `scale_trans` is
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# a transformation which scales `xt` and `yt` at transformation time
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# before applying the offsets. A typical use case is to use the figure
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# before applying the offsets.
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#
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# A typical use case is to use the figure
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# ``fig.dpi_scale_trans`` transformation for the `scale_trans` argument,
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# to first scale `xt` and `yt` specified in points to `display` space
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# before doing the final offset. The dpi and inches offset is a
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# 1/72 inches, and by specifying your offsets in points, your figure
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# will look the same regardless of the dpi resolution it is saved in.
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fig = plt.figure()
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ax = fig.add_subplot(111)
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fig, ax = plt.subplots()
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# make a simple sine wave
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x = np.arange(0., 2., 0.01)

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