Related
The ConnectionPatch is a useful way to draw a line between two points on two different axes (demo). Is it possible to use this class when one (or both) of the axes is of Cartopy GeoAxes type? A related answer suggests a work-around but I would prefer to avoid this.
I can not answer your question about the use of that class thing. But, if you are interested in plotting the lines between 2 different Cartopy geoaxes, or between matplotlib axes and a geoaxe, that can be achieved with some coordinate transformation. Here is a runnable code and the output plot. I have written some comments within the code to help explain the important steps.
For further information about coordinate system and tranformation:
Cartopy https://scitools.org.uk/cartopy/docs/latest/tutorials/understanding_transform.html
Since Cartopy is built on top of Matplotlib, you need to look into the related subject in Matplotlib.
Matplotlib https://matplotlib.org/3.2.1/tutorials/advanced/transforms_tutorial.html
import cartopy
import cartopy.mpl.geoaxes
import matplotlib.pyplot as plt
from mpl_toolkits.axes_grid1.inset_locator import inset_axes
fig, ax = plt.subplots()
fig.set_size_inches([8,8]) # 9,6; 8,9; 8,3 all OK
# Plot simple line on main axes
ax.plot([4,5,3,1,2])
p1 = [0.5,3.0] # Bangkok text location
p2 = [0.5,2.75] # Himalaya text location
# Plot texts (Bangkok, Himalaya) on the main axes
ax.text(*p1, "Bangkok", ha='right')
ax.text(*p2, "Himalaya", ha='right')
# Ploting on UR inset map (cartopy) on the main axes (ax)
bkk_lon, bkk_lat = 100, 13 # Bangkok
hml_lon, hml_lat = 83.32, 29.22 # Everest peak
# Create cartopy geoaxes inset axes as part of the main axes 'ax'
axins = inset_axes(ax, width="40%", height="30%", loc="upper right",
axes_class = cartopy.mpl.geoaxes.GeoAxes,
axes_kwargs = dict(map_projection = cartopy.crs.PlateCarree()))
# Set map limits on that axes (for Thailand)
llx, lly = 95, 0
urx, ury = 110, 25
axins.set_xlim((llx, urx))
axins.set_ylim((lly, ury))
# Plot coastlines
axins.add_feature(cartopy.feature.COASTLINE)
# Plot line across the inset mao, LL to UR; OK
#ll_p, ur_p = [llx,urx], [lly,ury]
#axins.plot(ll_p, ur_p, "r--")
axins.plot(bkk_lon, bkk_lat, 'ro', transform=cartopy.crs.PlateCarree()) # OK!
# Create another inset map on the main axes (ax)
axins2 = inset_axes(ax, width="40%", height="30%", loc="lower left",
axes_class = cartopy.mpl.geoaxes.GeoAxes,
axes_kwargs = dict(map_projection = cartopy.crs.PlateCarree()))
# Set map limits on that axes (second inset map)
llx2, lly2 = -60, -20
urx2, ury2 = 120, 90
axins2.set_xlim((llx2, urx2))
axins2.set_ylim((lly2, ury2))
axins2.add_feature(cartopy.feature.COASTLINE)
# Plot line from UK to BKK, OK
#p21, p22 = [0, 100], [40, 13]
#axins2.plot(p21, p22, "r--")
# Plot blue dot at Himalaya
axins2.plot(hml_lon, hml_lat, "bo")
plt.draw() # Do this to get updated position
# Do coordinate transformation to get BKK, HML locations in display coordinates
# from axins_data_xy to dp_xy
dpxy_bkk_axins = axins.transData.transform((bkk_lon, bkk_lat)) # get display coordinates
# from axins2_data_xy to dp_xy
dpxy_bkk_axins2 = axins2.transData.transform((hml_lon, hml_lat)) # get display coordinates
# Do coordinate transformation to get BKK, HML locations in data coordinates of the main axes 'ax'
# from both dp_xy to main_ax_data
ur_bkk = ax.transData.inverted().transform( dpxy_bkk_axins )
ll_hml = ax.transData.inverted().transform( dpxy_bkk_axins2 )
# Prep coordinates for line connecting BKK to HML
xs = ur_bkk[0], ll_hml[0]
ys = ur_bkk[1], ll_hml[1]
xs = ur_bkk[0], ll_hml[0]
ys = ur_bkk[1], ll_hml[1]
ax.plot(xs, ys, 'g--') # from Bkk to Himalaya of different inset maps
# Plot lines from texts (on main axes) to locations on maps
ax.plot([p1[0], ur_bkk[0]], [p1[1], ur_bkk[1]], 'y--')
ax.plot([p2[0], ll_hml[0]], [p2[1], ll_hml[1]], 'y--')
# Set cartopy inset background invisible
axins.background_patch.set_visible(False)
axins2.background_patch.set_visible(False)
plt.show()
The output plot:-
I'm trying to create a plot using pyplot that has a discontinuous x-axis. The usual way this is drawn is that the axis will have something like this:
(values)----//----(later values)
where the // indicates that you're skipping everything between (values) and (later values).
I haven't been able to find any examples of this, so I'm wondering if it's even possible. I know you can join data over a discontinuity for, eg, financial data, but I'd like to make the jump in the axis more explicit. At the moment I'm just using subplots but I'd really like to have everything end up on the same graph in the end.
Paul's answer is a perfectly fine method of doing this.
However, if you don't want to make a custom transform, you can just use two subplots to create the same effect.
Rather than put together an example from scratch, there's an excellent example of this written by Paul Ivanov in the matplotlib examples (It's only in the current git tip, as it was only committed a few months ago. It's not on the webpage yet.).
This is just a simple modification of this example to have a discontinuous x-axis instead of the y-axis. (Which is why I'm making this post a CW)
Basically, you just do something like this:
import matplotlib.pylab as plt
import numpy as np
# If you're not familiar with np.r_, don't worry too much about this. It's just
# a series with points from 0 to 1 spaced at 0.1, and 9 to 10 with the same spacing.
x = np.r_[0:1:0.1, 9:10:0.1]
y = np.sin(x)
fig,(ax,ax2) = plt.subplots(1, 2, sharey=True)
# plot the same data on both axes
ax.plot(x, y, 'bo')
ax2.plot(x, y, 'bo')
# zoom-in / limit the view to different portions of the data
ax.set_xlim(0,1) # most of the data
ax2.set_xlim(9,10) # outliers only
# hide the spines between ax and ax2
ax.spines['right'].set_visible(False)
ax2.spines['left'].set_visible(False)
ax.yaxis.tick_left()
ax.tick_params(labeltop='off') # don't put tick labels at the top
ax2.yaxis.tick_right()
# Make the spacing between the two axes a bit smaller
plt.subplots_adjust(wspace=0.15)
plt.show()
To add the broken axis lines // effect, we can do this (again, modified from Paul Ivanov's example):
import matplotlib.pylab as plt
import numpy as np
# If you're not familiar with np.r_, don't worry too much about this. It's just
# a series with points from 0 to 1 spaced at 0.1, and 9 to 10 with the same spacing.
x = np.r_[0:1:0.1, 9:10:0.1]
y = np.sin(x)
fig,(ax,ax2) = plt.subplots(1, 2, sharey=True)
# plot the same data on both axes
ax.plot(x, y, 'bo')
ax2.plot(x, y, 'bo')
# zoom-in / limit the view to different portions of the data
ax.set_xlim(0,1) # most of the data
ax2.set_xlim(9,10) # outliers only
# hide the spines between ax and ax2
ax.spines['right'].set_visible(False)
ax2.spines['left'].set_visible(False)
ax.yaxis.tick_left()
ax.tick_params(labeltop='off') # don't put tick labels at the top
ax2.yaxis.tick_right()
# Make the spacing between the two axes a bit smaller
plt.subplots_adjust(wspace=0.15)
# This looks pretty good, and was fairly painless, but you can get that
# cut-out diagonal lines look with just a bit more work. The important
# thing to know here is that in axes coordinates, which are always
# between 0-1, spine endpoints are at these locations (0,0), (0,1),
# (1,0), and (1,1). Thus, we just need to put the diagonals in the
# appropriate corners of each of our axes, and so long as we use the
# right transform and disable clipping.
d = .015 # how big to make the diagonal lines in axes coordinates
# arguments to pass plot, just so we don't keep repeating them
kwargs = dict(transform=ax.transAxes, color='k', clip_on=False)
ax.plot((1-d,1+d),(-d,+d), **kwargs) # top-left diagonal
ax.plot((1-d,1+d),(1-d,1+d), **kwargs) # bottom-left diagonal
kwargs.update(transform=ax2.transAxes) # switch to the bottom axes
ax2.plot((-d,d),(-d,+d), **kwargs) # top-right diagonal
ax2.plot((-d,d),(1-d,1+d), **kwargs) # bottom-right diagonal
# What's cool about this is that now if we vary the distance between
# ax and ax2 via f.subplots_adjust(hspace=...) or plt.subplot_tool(),
# the diagonal lines will move accordingly, and stay right at the tips
# of the spines they are 'breaking'
plt.show()
I see many suggestions for this feature but no indication that it's been implemented. Here is a workable solution for the time-being. It applies a step-function transform to the x-axis. It's a lot of code, but it's fairly simple since most of it is boilerplate custom scale stuff. I have not added any graphics to indicate the location of the break, since that is a matter of style. Good luck finishing the job.
from matplotlib import pyplot as plt
from matplotlib import scale as mscale
from matplotlib import transforms as mtransforms
import numpy as np
def CustomScaleFactory(l, u):
class CustomScale(mscale.ScaleBase):
name = 'custom'
def __init__(self, axis, **kwargs):
mscale.ScaleBase.__init__(self)
self.thresh = None #thresh
def get_transform(self):
return self.CustomTransform(self.thresh)
def set_default_locators_and_formatters(self, axis):
pass
class CustomTransform(mtransforms.Transform):
input_dims = 1
output_dims = 1
is_separable = True
lower = l
upper = u
def __init__(self, thresh):
mtransforms.Transform.__init__(self)
self.thresh = thresh
def transform(self, a):
aa = a.copy()
aa[a>self.lower] = a[a>self.lower]-(self.upper-self.lower)
aa[(a>self.lower)&(a<self.upper)] = self.lower
return aa
def inverted(self):
return CustomScale.InvertedCustomTransform(self.thresh)
class InvertedCustomTransform(mtransforms.Transform):
input_dims = 1
output_dims = 1
is_separable = True
lower = l
upper = u
def __init__(self, thresh):
mtransforms.Transform.__init__(self)
self.thresh = thresh
def transform(self, a):
aa = a.copy()
aa[a>self.lower] = a[a>self.lower]+(self.upper-self.lower)
return aa
def inverted(self):
return CustomScale.CustomTransform(self.thresh)
return CustomScale
mscale.register_scale(CustomScaleFactory(1.12, 8.88))
x = np.concatenate((np.linspace(0,1,10), np.linspace(9,10,10)))
xticks = np.concatenate((np.linspace(0,1,6), np.linspace(9,10,6)))
y = np.sin(x)
plt.plot(x, y, '.')
ax = plt.gca()
ax.set_xscale('custom')
ax.set_xticks(xticks)
plt.show()
Check the brokenaxes package:
import matplotlib.pyplot as plt
from brokenaxes import brokenaxes
import numpy as np
fig = plt.figure(figsize=(5,2))
bax = brokenaxes(
xlims=((0, .1), (.4, .7)),
ylims=((-1, .7), (.79, 1)),
hspace=.05
)
x = np.linspace(0, 1, 100)
bax.plot(x, np.sin(10 * x), label='sin')
bax.plot(x, np.cos(10 * x), label='cos')
bax.legend(loc=3)
bax.set_xlabel('time')
bax.set_ylabel('value')
A very simple hack is to
scatter plot rectangles over the axes' spines and
draw the "//" as text at that position.
Worked like a charm for me:
# FAKE BROKEN AXES
# plot a white rectangle on the x-axis-spine to "break" it
xpos = 10 # x position of the "break"
ypos = plt.gca().get_ylim()[0] # y position of the "break"
plt.scatter(xpos, ypos, color='white', marker='s', s=80, clip_on=False, zorder=100)
# draw "//" on the same place as text
plt.text(xpos, ymin-0.125, r'//', fontsize=label_size, zorder=101, horizontalalignment='center', verticalalignment='center')
Example Plot:
For those interested, I've expanded upon #Paul's answer and added it to the matplotlib wrapper proplot. It can do axis "jumps", "speedups", and "slowdowns".
There is no way currently to add "crosses" that indicate the discrete jump like in Joe's answer, but I plan to add this in the future. I also plan to add a default "tick locator" that sets sensible default tick locations depending on the CutoffScale arguments.
Adressing Frederick Nord's question how to enable parallel orientation of the diagonal "breaking" lines when using a gridspec with ratios unequal 1:1, the following changes based on the proposals of Paul Ivanov and Joe Kingtons may be helpful. Width ratio can be varied using variables n and m.
import matplotlib.pylab as plt
import numpy as np
import matplotlib.gridspec as gridspec
x = np.r_[0:1:0.1, 9:10:0.1]
y = np.sin(x)
n = 5; m = 1;
gs = gridspec.GridSpec(1,2, width_ratios = [n,m])
plt.figure(figsize=(10,8))
ax = plt.subplot(gs[0,0])
ax2 = plt.subplot(gs[0,1], sharey = ax)
plt.setp(ax2.get_yticklabels(), visible=False)
plt.subplots_adjust(wspace = 0.1)
ax.plot(x, y, 'bo')
ax2.plot(x, y, 'bo')
ax.set_xlim(0,1)
ax2.set_xlim(10,8)
# hide the spines between ax and ax2
ax.spines['right'].set_visible(False)
ax2.spines['left'].set_visible(False)
ax.yaxis.tick_left()
ax.tick_params(labeltop='off') # don't put tick labels at the top
ax2.yaxis.tick_right()
d = .015 # how big to make the diagonal lines in axes coordinates
# arguments to pass plot, just so we don't keep repeating them
kwargs = dict(transform=ax.transAxes, color='k', clip_on=False)
on = (n+m)/n; om = (n+m)/m;
ax.plot((1-d*on,1+d*on),(-d,d), **kwargs) # bottom-left diagonal
ax.plot((1-d*on,1+d*on),(1-d,1+d), **kwargs) # top-left diagonal
kwargs.update(transform=ax2.transAxes) # switch to the bottom axes
ax2.plot((-d*om,d*om),(-d,d), **kwargs) # bottom-right diagonal
ax2.plot((-d*om,d*om),(1-d,1+d), **kwargs) # top-right diagonal
plt.show()
This is a hacky but pretty solution for x-axis breaks.
The solution is based on https://matplotlib.org/stable/gallery/subplots_axes_and_figures/broken_axis.html, which gets rid of the problem with positioning the break above the spine, solved by How can I plot points so they appear over top of the spines with matplotlib?
from matplotlib.patches import Rectangle
import matplotlib.pyplot as plt
def axis_break(axis, xpos=[0.1, 0.125], slant=1.5):
d = slant # proportion of vertical to horizontal extent of the slanted line
anchor = (xpos[0], -1)
w = xpos[1] - xpos[0]
h = 1
kwargs = dict(marker=[(-1, -d), (1, d)], markersize=12, zorder=3,
linestyle="none", color='k', mec='k', mew=1, clip_on=False)
axis.add_patch(Rectangle(
anchor, w, h, fill=True, color="white",
transform=axis.transAxes, clip_on=False, zorder=3)
)
axis.plot(xpos, [0, 0], transform=axis.transAxes, **kwargs)
fig, ax = plt.subplots(1,1)
plt.plot(np.arange(10))
axis_break(ax, xpos=[0.1, 0.12], slant=1.5)
axis_break(ax, xpos=[0.3, 0.31], slant=-10)
if you want to replace an axis label, this would do the trick:
from matplotlib import ticker
def replace_pos_with_label(fig, pos, label, axis):
fig.canvas.draw() # this is needed to set up the x-ticks
labs = axis.get_xticklabels()
labels = []
locs = []
for text in labs:
x = text._x
lab = text._text
if x == pos:
lab = label
labels.append(lab)
locs.append(x)
axis.xaxis.set_major_locator(ticker.FixedLocator(locs))
axis.set_xticklabels(labels)
fig, ax = plt.subplots(1,1)
plt.plot(np.arange(10))
replace_pos_with_label(fig, 0, "-10", axis=ax)
replace_pos_with_label(fig, 6, "$10^{4}$", axis=ax)
axis_break(ax, xpos=[0.1, 0.12], slant=2)
I am working some meteorological data to plot contour lines on a basemap. The full working example code I have done earlier is here How to remove/omit smaller contour lines using matplotlib. All works fine and I don’t complain with the contour plot. However there is a special case that I have to hide all contour lines over a specific region (irregular lat & lon) on a Basemap.
The only possible solution I can think of is to draw a ploygon lines over a desired region and fill with the color of same as Basemap. After lot of search I found this link How to draw rectangles on a Basemap (code below)
from mpl_toolkits.basemap import Basemap
import numpy as np
import matplotlib.pyplot as plt
from matplotlib.patches import Polygon
def draw_screen_poly( lats, lons, m):
x, y = m( lons, lats )
xy = zip(x,y)
poly = Polygon( xy, facecolor='red', alpha=0.4 )
plt.gca().add_patch(poly)
lats = [ -30, 30, 30, -30 ]
lons = [ -50, -50, 50, 50 ]
m = Basemap(projection='sinu',lon_0=0)
m.drawcoastlines()
m.drawmapboundary()
draw_screen_poly( lats, lons, m )
plt.show()
It seems to work partially. However, I want to draw a region which is irregular.
Any solution is appreciated.
Edit: 1
I have understood where the problem is. It seems that any colour (facecolor) filled within the polygon region does not make it hide anything below. Always it is transparent only, irrespective of alpha value used or not. To illustrate the problem, I have cropped the image which has all three regions ie. contour, basemap region and polygon region. Polygon region is filled with red colour but as you can see, the contour lines are always visible. The particular line I have used in the above code is :-
poly = Polygon(xy, facecolor='red', edgecolor='b')
Therefore the problem is not with the code above. It seem the problem with the polygon fill. But still no solution for this issue. The resulting image (cropped image) is below (See my 2nd edit below the attached image):-
Edit 2:
Taking clue from this http://matplotlib.1069221.n5.nabble.com/Clipping-a-plot-inside-a-polygon-td41950.html which has the similar requirement of mine, I am able to remove some the data. However, the removed data is only from outside of polygon region instead of within. Here is the code I have taken clue from:-
import numpy as np
import matplotlib.pyplot as plt
from matplotlib.patches import RegularPolygon
data = np.arange(100).reshape(10, 10)
fig = plt.figure()
ax = fig.add_subplot(111)
ax.contourf(data)
poly = RegularPolygon([ 0.5, 0.5], 6, 0.4, fc='none',
ec='k', transform=ax.transAxes)
for artist in ax.get_children():
artist.set_clip_path(poly)
Now my question is that what command is used for removing the data within the polygon region?
Didn't noticed there was a claim on this so I might just give the solution already proposed here. You can tinker with the zorder to hide stuff behind your polygon:
import matplotlib
import matplotlib.mlab as mlab
import matplotlib.pyplot as plt
matplotlib.rcParams['xtick.direction'] = 'out'
matplotlib.rcParams['ytick.direction'] = 'out'
delta = 0.025
x = np.arange(-3.0, 3.0, delta)
y = np.arange(-2.0, 2.0, delta)
X, Y = np.meshgrid(x, y)
Z1 = mlab.bivariate_normal(X, Y, 1.0, 1.0, 0.0, 0.0)
Z2 = mlab.bivariate_normal(X, Y, 1.5, 0.5, 1, 1)
# difference of Gaussians
Z = 10.0 * (Z2 - Z1)
# Create a simple contour plot with labels using default colors. The
# inline argument to clabel will control whether the labels are draw
# over the line segments of the contour, removing the lines beneath
# the label
fig = plt.figure()
ax = fig.add_subplot(111)
CS = plt.contour(X, Y, Z,zorder=3)
plt.clabel(CS, inline=1, fontsize=10)
plt.title('Simplest default with labels')
rect1 = matplotlib.patches.Rectangle((0,0), 2, 1, color='white',zorder=5)
ax.add_patch(rect1)
plt.show()
, the result is:
In matplotlib how to overlay the shapefile (available in folder) as attached below at the top right position outside the plot.
The code referenced by banderkat:
import matplotlib.pyplot as plt
import Image
import numpy as np
im = Image.open('Jbc4j.jpg')
width = im.size[0]
height = im.size[1]
# We need a float array between 0-1, rather than
# a uint8 array between 0-255
im = np.array(im).astype(np.float) / 255
a = np.random.randint(0,100,100)
b = range(100)
fig = plt.figure(1,figsize=(5, 7), dpi=80, facecolor='w')
ax = fig.add_subplot(111)
ax.scatter(a,b)
fig.canvas.draw()
# With newer (1.0) versions of matplotlib, you can
# use the "zorder" kwarg to make the image overlay
# the plot, rather than hide behind it... (e.g. zorder=10)
fig.figimage(im, fig.bbox.xmax - width, fig.bbox.ymax - height, zorder=0)
# (Saving with the same dpi as the screen default to
# avoid displacing the logo image)
fig.savefig('temp.png', dpi=80)
plt.show()
Produces the following result (imaged cropped to save space).
Changing the zorder=1 will place the image on top.
Other helpful references:
How to change background color for scatter plot in matplotlib
How do you change the size of figures drawn with matplotlib?
Python/Matplotlib - Change the relative size of a subplot
In Matplotlib, what does the argument mean in fig.add_subplot(111)?
Customizing Location of Subplot Using GridSpec
You can use basemap toolkit to load and plot shapefile. Here I've plotted shapeFile in a separate axes and aligned it to top-right of other axes plot using 'subplot2grid'.
import numpy as np
import matplotlib.pyplot as plt
from mpl_toolkits.basemap import Basemap
import matplotlib.gridspec as gridspec
def plotShapeFile():
# Lambert Conformal Conic map.
m = Basemap(llcrnrlon=-100.,llcrnrlat=0.,urcrnrlon=-20.,urcrnrlat=57.,
projection='lcc',lat_1=20.,lat_2=40.,lon_0=-60.,
resolution ='l',area_thresh=1000.)
# read shapefile.
shp_info = m.readshapefile('C:/basemap-1.0.6/basemap-1.0.6/examples/huralll020','hurrtracks',drawbounds=False)
# find names of storms that reached Cat 4.
names = []
for shapedict in m.hurrtracks_info:
cat = shapedict['CATEGORY']
name = shapedict['NAME']
if cat in ['H4','H5'] and name not in names:
# only use named storms.
if name != 'NOT NAMED': names.append(name)
# plot tracks of those storms.
for shapedict,shape in zip(m.hurrtracks_info,m.hurrtracks):
name = shapedict['NAME']
cat = shapedict['CATEGORY']
if name in names:
xx,yy = zip(*shape)
# show part of track where storm > Cat 4 as thick red.
if cat in ['H4','H5']:
m.plot(xx,yy,linewidth=1.5,color='r')
elif cat in ['H1','H2','H3']:
m.plot(xx,yy,color='k')
# draw coastlines, meridians and parallels.
m.drawcoastlines()
m.drawcountries()
m.drawmapboundary(fill_color='#99ffff')
m.fillcontinents(color='#cc9966',lake_color='#99ffff')
m.drawparallels(np.arange(10,70,20),labels=[1,1,0,0])
m.drawmeridians(np.arange(-100,0,20),labels=[0,0,0,1])
if __name__ == '__main__':
fig=plt.figure()
plt.subplots_adjust(wspace=0.001, hspace=0.001)
ax1=plt.subplot2grid((5,5), (0,0), colspan=4, rowspan=4)
labels = 'Frogs', 'Hogs', 'Dogs', 'Logs'
fracs = [15,30,45, 10]
explode=(0, 0.05, 0, 0)
p1,t1,at1 = plt.pie(fracs, explode=explode, labels=labels, autopct='%1.1f%%', shadow=True)
plt.title('Raining Hogs and Dogs', bbox={'facecolor':'0.8', 'pad':5})
ax2=plt.subplot2grid((5,5), (0,4), colspan=1, rowspan=1)
#draw shapeFile on the current active axes, i.e. ax2
plotShapeFile()
plt.tight_layout()
plt.show()
Below are links to references I've used:
http://sourceforge.net/projects/matplotlib/files/matplotlib-toolkits/basemap-1.0.6/
http://matplotlib.org/basemap/users/examples.html
Output:
Originally, I was hoping that I could create a sort of a class for a marker in matplotlib, which would be a square with text showing the, say, x coordinate and a label, so I could instantiate it with something like (pseudocode):
plt.plot(..., marker=myMarkerClass(label="X:"), ... )
... but as far as I can see, you cannot do stuff like that.
However, it seems that customization of markers is not available in older matplotlib; so I'd like to reduce my question to: how to get custom (path) markers in older matplotlib, so their sizes are defined in screen coordinates (so markers don't scale upon zoom)? To clarify, here are some examples:
Default (uncustomized) markers
Below is an example with the default matplotlib markers, which works with older matplotlib. Note that I've tried instead of using pyplot.plot(), I'm trying to work with matplotlib.figure.Figure directly (as that is the form usually used with diverse backends), requiring use of "figure manager" (see also matplotlib-devel - Backends object structure):
import matplotlib
import matplotlib.pyplot as plt
import matplotlib.figure
import numpy as np
t = np.arange(0.0,1.5,0.25)
s = np.sin(2*np.pi*t)
mfigure = matplotlib.figure.Figure(figsize=(5,4), dpi=100)
ax = mfigure.add_subplot(111)
ax.plot(t,s, marker='o', color='b', markerfacecolor='orange', markersize=10.0)
fig = plt.figure() # create something (fig num 1) for fig_manager
figman = matplotlib._pylab_helpers.Gcf.get_fig_manager(1)
figman.canvas.figure = mfigure # needed
mfigure.set_canvas(figman.canvas) # needed
plt.show()
If we do an arbitrary zoom rect here, the markers remain the same size:
Customized markers via Path
This is documented in artists (Line2D.set_marker) — Matplotlib 1.2.1 documentation; however, it doesn't work with older matplotlib; here's an example:
import matplotlib
import matplotlib.pyplot as plt
import matplotlib.figure
import matplotlib.path
import numpy as np
print("matplotlib version {0}".format(matplotlib.__version__))
def getCustomSymbol1(inx, iny, sc, yasp):
verts = [
(-0.5, -0.5), # left, bottom
(-0.5, 0.5), # left, top
(0.5, 0.5), # right, top
(0.5, -0.5), # right, bottom
(-0.5, -0.5), # ignored
]
codes = [matplotlib.path.Path.MOVETO,
matplotlib.path.Path.LINETO,
matplotlib.path.Path.LINETO,
matplotlib.path.Path.LINETO,
matplotlib.path.Path.CLOSEPOLY,
]
pathCS1 = matplotlib.path.Path(verts, codes)
return pathCS1, verts
t = np.arange(0.0,1.5,0.25)
s = np.sin(2*np.pi*t)
mfigure = matplotlib.figure.Figure(figsize=(5,4), dpi=100)
ax = mfigure.add_subplot(111)
pthCS1, vrtCS1 = getCustomSymbol1(0,0, 1,1)
# here either marker=pthCS1 or marker=np.array(vrtCS1)
# have the same effect:
ax.plot(t,s, marker=pthCS1, markerfacecolor='orange', markersize=10.0)
#ax.plot(t,s, marker=np.array(vrtCS1), markerfacecolor='orange', markersize=10.0)
fig = plt.figure() # create something (fig num 1) for fig_manager
figman = matplotlib._pylab_helpers.Gcf.get_fig_manager(1)
figman.canvas.figure = mfigure # needed
mfigure.set_canvas(figman.canvas) # needed
plt.show()
This runs fine for me in newer matplotlib, but fails in the older:
$ python3.2 test.py
matplotlib version 1.2.0
$ python2.7 test.py # marker=pthCS1
matplotlib version 0.99.3
Traceback (most recent call last):
File "test.py", line 36, in <module>
ax.plot(t,s, marker=pthCS1, markerfacecolor='orange', markersize=10.0)
...
File "/usr/lib/pymodules/python2.7/matplotlib/lines.py", line 804, in set_marker
self._markerFunc = self._markers[marker]
KeyError: Path([[-0.5 -0.5]
[-0.5 0.5]
[ 0.5 0.5]
[ 0.5 -0.5]
[-0.5 -0.5]], [ 1 2 2 2 79])
$ python2.7 test.py # marker=np.array(vrtCS1)
matplotlib version 0.99.3
Traceback (most recent call last):
File "test.py", line 38, in <module>
ax.plot(t,s, marker=np.array(vrtCS1), markerfacecolor='orange', markersize=10.0)
...
File "/usr/lib/pymodules/python2.7/matplotlib/lines.py", line 798, in set_marker
if marker not in self._markers:
TypeError: unhashable type: 'numpy.ndarray'
However, when it works in Python 3.2, the markers again keep their size across zoom of the graph, as I'd expect:
... though note this issue: Custom marker created from vertex list scales wrong · Issue #1980 · matplotlib/matplotlib · GitHub, in respect to this type of custom markers.
Through Paths in PatchCollection
I've picked up parts of this code from some internet postings, but cannot find the links now. In any case, we can avoid drawing the markers and PatchCollection can be used, to draw what should be the markers. Here is the code, which runs in older matplotlib:
import matplotlib
import matplotlib.pyplot as plt
import matplotlib.figure
import matplotlib.path, matplotlib.patches, matplotlib.collections
import numpy as np
def getCustomSymbol1(inx, iny, sc, yasp):
verts = [
(inx-0.5*sc, iny-0.5*sc*yasp), # (0., 0.), # left, bottom
(inx-0.5*sc, iny+0.5*sc*yasp), # (0., 1.), # left, top
(inx+0.5*sc, iny+0.5*sc*yasp), # (1., 1.), # right, top
(inx+0.5*sc, iny-0.5*sc*yasp), # (1., 0.), # right, bottom
(inx-0.5*sc, iny-0.5*sc*yasp), # (0., 0.), # ignored
]
codes = [matplotlib.path.Path.MOVETO,
matplotlib.path.Path.LINETO,
matplotlib.path.Path.LINETO,
matplotlib.path.Path.LINETO,
matplotlib.path.Path.CLOSEPOLY,
]
pathCS1 = matplotlib.path.Path(verts, codes)
return pathCS1
def getXyIter(inarr):
# this supports older numpy, where nditer is not available
if np.__version__ >= "1.6.0":
return np.nditer(inarr.tolist())
else:
dimensions = inarr.shape
xlen = dimensions[1]
xinds = np.arange(0, xlen, 1)
return np.transpose(np.take(inarr, xinds, axis=1))
t = np.arange(0.0,1.5,0.25)
s = np.sin(2*np.pi*t)
mfigure = matplotlib.figure.Figure(figsize=(5,4), dpi=100)
ax = mfigure.add_subplot(111)
ax.plot(t,s)
customMarkers=[]
for x, y in getXyIter(np.array([t,s])): #np.nditer([t,s]):
#printse("%f:%f\n" % (x,y))
pathCS1 = getCustomSymbol1(x,y,0.05,1.5*500.0/400.0)
patchCS1 = matplotlib.patches.PathPatch(pathCS1, facecolor='orange', lw=1) # no
customMarkers.append(patchCS1)
pcolm = matplotlib.collections.PatchCollection(customMarkers)
pcolm.set_alpha(0.9)
ax.add_collection(pcolm)
fig = plt.figure() # create something (fig num 1) for fig_manager
figman = matplotlib._pylab_helpers.Gcf.get_fig_manager(1)
figman.canvas.figure = mfigure # needed
mfigure.set_canvas(figman.canvas) # needed
plt.show()
Now, here I tried to take figure initial aspect ratio into consideration and indeed, at first render, the "markers" look right in respect to size - but...:
... when we try to do arbitrary zoom, it is obvious that the paths have been specified in data coordinates, and so their sizes change depending on the zoom rect. (Another nuissance is that facecolor='orange' is not obeyed; but that can be fixed with pcolm.set_facecolor('orange'))
So, is there a way that I can use PatchCollection as markers for older matplotlib, in the sense that the rendered paths would be defined in screen coordinates, so they would not change their size upon arbitrary zooming?
Many thanks to #tcaswell for the comment on blended transform - in trying to figure out why that doesn't work for me, I finally found the solution. First, the code - using, essentially, the default marker engine of matplotlib (depending on whether using older matplotlib (0.99) or newer one):
import matplotlib
import matplotlib.pyplot as plt
import matplotlib.figure
import numpy as np
# create vertices and Path of custom symbol
def getCustomSymbol1():
verts = [
(0.0, 0.0), # left, bottom
(0.0, 0.7), # left, top
(1.0, 1.0), # right, top
(0.8, 0.0), # right, bottom
(0.0, 0.0), # ignored
]
codes = [matplotlib.path.Path.MOVETO,
matplotlib.path.Path.LINETO,
matplotlib.path.Path.LINETO,
matplotlib.path.Path.LINETO,
matplotlib.path.Path.CLOSEPOLY,
]
pathCS1 = matplotlib.path.Path(verts, codes)
return pathCS1, verts
if matplotlib.__version__ < "1.0.0":
# define a marker drawing function, that uses
# the above custom symbol Path
def _draw_mypath(self, renderer, gc, path, path_trans):
gc.set_snap(renderer.points_to_pixels(self._markersize) >= 2.0)
side = renderer.points_to_pixels(self._markersize)
transform = matplotlib.transforms.Affine2D().translate(-0.5, -0.5).scale(side)
rgbFace = self._get_rgb_face()
mypath, myverts = getCustomSymbol1()
renderer.draw_markers(gc, mypath, transform,
path, path_trans, rgbFace)
# add this function to the class prototype of Line2D
matplotlib.lines.Line2D._draw_mypath = _draw_mypath
# add marker shortcut/name/command/format spec '#' to Line2D class,
# and relate it to our custom marker drawing function
matplotlib.lines.Line2D._markers['#'] = '_draw_mypath'
matplotlib.lines.Line2D.markers = matplotlib.lines.Line2D._markers
else:
import matplotlib.markers
def _set_mypath(self):
self._transform = matplotlib.transforms.Affine2D().translate(-0.5, -0.5)
self._snap_threshold = 2.0
mypath, myverts = getCustomSymbol1()
self._path = mypath
self._joinstyle = 'miter'
matplotlib.markers.MarkerStyle._set_mypath = _set_mypath
matplotlib.markers.MarkerStyle.markers['#'] = 'mypath'
matplotlib.lines.Line2D.markers = matplotlib.markers.MarkerStyle.markers
# proceed as usual - use the new marker '#'
t = np.arange(0.0,1.5,0.25)
s = np.sin(2*np.pi*t)
mfigure = matplotlib.figure.Figure(figsize=(5,4), dpi=100)
ax = mfigure.add_subplot(111)
ax.plot(t,s, marker='#', color='b', markerfacecolor='orange', markersize=20.0)
fig = plt.figure() # create something (fig num 1) for fig_manager
figman = matplotlib._pylab_helpers.Gcf.get_fig_manager(1)
figman.canvas.figure = mfigure # needed
mfigure.set_canvas(figman.canvas) # needed
plt.show()
It shows a slightly "creative" marker (if I may say so myself :) ) - and this is how it behaves under zoom:
... that is, exactly as I want it - markers keep their position in data coordinates; however preserve their size under zooming.
Discussion
One of the most confusing things for me here, was the following: Essentially, you can specify a rectangle through an x,y coordinate as "location", and size (height/width). So if I specify a rectangle at x,y=(2,3); with halfsize 2 (so, square); then I can calculate its path as vertices through:
[(x-hs,y-hs), (x-hs,y+hs), (x+hs,y+hs), (x+hs,y-hs)]
This is, essentially, what getCustomSymbol1 was trying to return all along. In addition, for instance matplotlib.patches.Rectangle is instantiated through location and size, as in Rectangle((x,y), width, height).
Now, the problem is - what I actually wanted, is that markers, as shapes, stay on their position - in data coordinates, so moving and zooming the graph keeps their position as data; however, they should have kept their size under zooming.
This means that I want (x,y) specified in one coordinate system (data), and size (or width, height, or halfsize) specified in another coordinate system, in this case, the screen coordinate system: since I want the shapes to keep their size under zoom, I actually want to keep their size in screen pixels the same!
That is why no transformation as such would help in my case - any transformation would work on all the vertices of a path, as interpreted in a single coordinate system! Whereas, what I want, would be to get something like:
hsd = screen2dataTransform(10px)
[(x-hsd,y-hsd), (x-hsd,y+hsd), (x+hsd,y+hsd), (x+hsd,y-hsd)]
... and this recalculation of the vertices of the marker path would have to be repeated each time the zoom level, or the figure pan, or the window size changes.
As such, vertices/paths (and patches) and transformation alone cannot be used for this purpose. However, thankfully, we can use matplotlibs own engine; we simply have to know that any call to ax.plot(...marker=...) actually delegates the drawing of markers to matplotlib.lines.Line2D; and Line2D maintains an internal dict, which relates the marker one-character format specifier/command (like 'o', '*' etc) to a specific drawing function; and the drawing function, finally, does the size transformation in code like (in the solution code above, the drawing is for the most part taken from the 's' (square) marker implementation):
side = renderer.points_to_pixels(self._markersize)
transform = matplotlib.transforms.Affine2D().translate(-0.5, -0.5).scale(side)
Note that this is the case for older matplotlib (0.99.3 in my case); for newer matplotlib (1.2.0 in my case), there is a separate class MarkerStyle which maintains the relationship between the marker format specifier, and the function - and the function is not _draw_ anymore, it is just _set_ - but other than that, it is the same principle.
NB: I'm actually not sure when MarkerStyle was introduced, I could only find matplotlib.markers — Matplotlib 1.3.x documentation and it doesn't say; so that if matplotlib.__version__ < "1.0.0": in the code above could be wrong; but worksforme (fornow).
Because the markers size is, so to speak, managed separately (from its position) - that means that you don't have to do any special calculation in your custom marker Path specification; all you need to do is make sure its vertices fit in the range (0.0,0.0) to (1.0, 1.0) - the marker drawing engine will do the rest.
Well, I hope I understood this right - but if there are other approaches that work like this, I'd sure like to know about those :)
Hope this helps someone,
Cheers!