Add a hex tiling glyph

[birdsarah]

hex binning is useful (https://cran.r-project.org/web/packages/hexbin/vignettes/hexagon_binning.pdf) and I've seen a lot of cool hexmaps recently: http://www.theguardian.com/politics/ng-interactive/2016/jun/23/eu-referendum-live-results-and-analysis

[crashMOGWAI]

merge with #4342

[bryevdv]

Drawing a hex glyph would be trivial, I guess the interesting part is integrating a hex coordinate system reasonably.

[birdsarah]

Well if it was basically a marker (so it was just an x y center) then users could figure it out for now.

Sarah Bird
sbird@continuum.io

On Jul 12, 2016, at 2:55 PM, Bryan Van de Ven notifications@github.com wrote:

Drawing a hex glyph would be trivial, I guess the interesting part is integrating a hex coordinate system reasonably.

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[crashMOGWAI]

Would need to be more robust than a marker for feature rich binning visualizations

[bryevdv]

@birdsarah I'm -1 on adding a hard-to-use for things-people-really-want interface, and accumulating knowledge on here, SO and the mailing list that will only have to be updated/countered/deprecated later. Offhand, I think a Hex glyphs might have:

origin = Tuple # cartesian axis coords to "anchor" hex coord system, default (0,0)

size = Float # how big the hex tiles grid is (measured along diag?)

angle = Float # global rotation about origin for the hex grid (optional)

hx = DataSpec # "hex" x coords -- should be integer only 

hy = DataSpec # "hex" y coords -- should be integer only 

This is off the top of my head. We should compare to what other systems do. Whatever we do, I think there are the same/similar problems that e.g. circles have in non 1-1 coordinate systems.

[StevenCHowell]

Looking at the matplotlib and R implementation of hexbin, this seems like two separate issues:

1. Adding a hexagon marker than can be used for representing data points
2. Adding a hexagonal binning and plotting algorithm

The hexagonal binning and plotting algorithm could use hexagon markers/glyphs but this would likely lead to overlapping similar to issue #3315, in which histogram bars overlap. Also, it makes sense for the hexagon marker (point 1) to have a symmetric shape regardless of the plot aspect ratio. For binning and plotting data using a hexagonal grid, it would make sense to have non-symmetric hexagons which match the aspect ratio of the plot. See attached demo showing a zoomed in version of matplotlib's implementation.

[crashMOGWAI]

Agree with @stvn66. Looks like there are a couple of ideas bouncing around that could compliment each other as incremental development goals.

• hex glyph for data points/ markers
• 'respect aspect' mode for hex glyph (suggested by @brevdv in Glyph/Zoom Sanity Check #4802)
• hex binning and plotting algorithm/ multi-purpose mesh or grid feature

[StevenCHowell]

These examples from the D3 gallery show two options of visualizing a hexbin plot:

1. Color Encoding (used for the matplotlib implementation of hexbin)
2. Area Encoding

This second option may be more complicated to get the scaling of markers/glyphs to match the scaling of the plotting area when using different scaling for the x/y axes.

[StevenCHowell]

How much overlap is there between the bokehjs in rbokeh and python bokeh? I just saw that rbokeh has hexbin plots.

[bryevdv]

100% overlap, RBokeh uses the same BokehJS as-is. AFAIK (or have to assume) RBokeh supports hex charts by computing hexagon coordinates in R and drawing as Patches

[hafen]

That's correct.

[bryevdv]

This is obviously an old discussion but I'm interested in reviving it. I think there are two separate things, both worth doing:

• a Hex marker, that is just an x,y,size, angle scatter marker. This should pretty trivial, ref previous work: Stvn66 4786 hex markers #4827

• HexTileglyph that draws non-overlapping hex tiles in a hex tile coordinate system.