Add Figure.hlines for plotting horizontal lines

[michaelgrund]

As discussed in #670 here's a new module (hlines) to plot a single or a set of horizontal lines with only defining the desired y-value(s). For discussion I only add the module for horizontal lines at the moment, however, the adjustments to prepare the same for vertical lines is done very quickly. Furthermore, currently the whole procedure is performed in a loop since it's not possible to pass multi-segment lines to the plot function so far (except using an input file). Please correct me if I'm wrong.

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[seisman]

@michaelgrund Nice work! I just changed the PR title so that we can focus on one feature Figure.hlines in this PR.

[seisman]

Furthermore, currently the whole procedure is performed in a loop since it's not possible to pass multi-segment lines to the plot function so far (except using an input file).

It's possible to use np.NaN record to separate segments:

import numpy as np
import pygmt

x = np.array([2, 4, 4, np.NaN, 5, 6])
y = np.array([3, 5, 7, np.NaN, 4, 2])

fig = pygmt.Figure()
fig.basemap(region=[0, 10, 0, 10], frame=True)
fig.plot(x, y, pen="2p")
fig.show()

but I'm not sure if other features (lines with different colors) are supported.

[michaelgrund]

Furthermore, currently the whole procedure is performed in a loop since it's not possible to pass multi-segment lines to the plot function so far (except using an input file).

It's possible to use np.NaN record to separate segments:

import numpy as np
import pygmt

x = np.array([2, 4, 4, np.NaN, 5, 6])
y = np.array([3, 5, 7, np.NaN, 4, 2])

fig = pygmt.Figure()
fig.basemap(region=[0, 10, 0, 10], frame=True)
fig.plot(x, y, pen="2p")
fig.show()

but I'm not sure if other features (lines with different colors) are supported.

Ok will check that and, if possible, adjust the code.

[willschlitzer]

@GenericMappingTools/pygmt-maintainers This PR has been untouched since August; are we planning to get it wrapped up for v0.5.0?

[maxrjones]

@GenericMappingTools/pygmt-maintainers This PR has been untouched since August; are we planning to get it wrapped up for v0.5.0?

I think the issues raised in #923 (review) will be a bit tricky to address, so I suggest v0.6.0.

[willschlitzer]

@GenericMappingTools/pygmt-maintainers This PR has been untouched since August; are we planning to get it wrapped up for v0.5.0?

I think the issues raised in #923 (review) will be a bit tricky to address, so I suggest v0.6.0.

@michaelgrund I'm going to bump this back to v0.6.0

[michaelgrund]

@GenericMappingTools/pygmt-maintainers This PR has been untouched since August; are we planning to get it wrapped up for v0.5.0?

I think the issues raised in #923 (review) will be a bit tricky to address, so I suggest v0.6.0.

@michaelgrund I'm going to bump this back to v0.6.0

That's fine @willschlitzer. Totally overlooked the review comments from @meghanrjones. Sorry for that.

[willschlitzer]

@michaelgrund Are you hoping to get this in to the v0.6 release?

[michaelgrund]

@michaelgrund Are you hoping to get this in to the v0.6 release?

Unfortunately not @willschlitzer ... Hope I can continue working on this PR end of February/beginning of March. Set the milestone to v0.7.0.

[seisman]

@michaelgrund I think we should get this feature done in v0.13.0. Are you still interested in working on this PR?

[michaelgrund]

@michaelgrund I think we should get this feature done in v0.13.0. Are you still interested in working on this PR?

Yes I am, after 3 years we should definitely bring this in v0.13.0.

[seisman]

Use the Figure.region property (https://www.pygmt.org/dev/api/generated/pygmt.Figure.html#pygmt-figure):

Suggested change

	with Session() as lib:
	# get limits from current map boundings if not given
	# via xmin, xmax
	x = np.array([[lib.extract_region()[0]], [lib.extract_region()[1]]])
	x = np.repeat(x, list_length, axis=1)
	# get limits from current map boundings if not given via xmin, xmax
	xmin, xmax = fig.region[0:2]
	x = np.repeat([[xmin], [xmax]], list_length, axis=1)