geom_polygonraster - grey lines between pixels

[ThomasLuypaert]

Hi Teun,

First of all, thanks a lot for making this package, you've saved me a lot of time and trouble trying to plot rasters in the polar coordinate system. I'm using your function to map daily patterns in the occurrence of sound over a certain period. I'm getting very close to the plot I want to produce, with one final hurdle: there are always grey lines in between my pixels.

I've encountered this issue before in ggplot with geom_tile, where this can be resolved by setting both the color and fill options. However, this does not seem to help using geom_polygonraster.

Here is an example of a plot I'm getting:

As you can see, there are faint grey lines between my pixels, which creates a weird star-shaped pattern in some areas of the plot.

Here is the code I'm using to produce this plot:

polar_plot <- 

  ggplot(Fuzaca_df_long, aes(x = variable, y = as.numeric(frequency), color = value, fill = value))+

  ggh4x::geom_polygonraster()+

  scale_color_viridis_c(option = "A", end = 1, na.value = "black")+

  scale_fill_viridis_c(option = "A", end = 1, na.value = "black")+

  scale_x_discrete(expand = c(0,0))+
  scale_y_discrete(expand = c(0,0))+

  coord_polar()+

  theme(
    axis.line = element_blank(), 
    axis.text = element_blank(), 
    axis.title = element_blank(), 
    axis.ticks = element_blank(), 
    plot.background = element_rect(color = "black", fill = "black"), 
    panel.background = element_rect(color = "black", fill = "black"), 
    plot.margin = element_blank()
  ) 

If you have any suggestions on how this behaviour may be avoided, that would help me out a great deal!

Cheers, Thomas

[teunbrand]

Hi Thomas,

Thanks for filing this issue. Unfortunately, there isn't a lot that I can do as the underlying problem originates in the graphics device. In particular, the anti-aliasing setting, that for most but not all devices anti-aliases lines but not fills, causes the Moiré patterning you see as stars in your plot. I wish I had a better solution, but if you can control this with geom_tile(), wouldn't that just work better?

[ThomasLuypaert]

Hi Teun,

Thanks for getting back to me on this so quickly, and for explaining what is causing this issue.

Yes, technically I could achieve the same thing using geom_tile with coord_polar, however there are two issues:

1. It is MUCH slower for a plot with this many pixels
2. I can't seem to close the gap that connects the start of the polar coordinate plot with the end (example below)

Here is an example of what I mean by point 2 (notice the gap at 00:00):

I've tried setting expand = c(0,0), but that does not solve the issue...

I know this is not an issue with your package, but if you've got any idea on how I might solve this issue with geom_tile, that would be hugely helpful :)

[teunbrand]

Well you might be interested to try the dev version of ggplot2 for this because drawing rectangles in polar coordinates have been sped up considerably for many rectangles (see https://github.com/tidyverse/ggplot2/pull/5081). I can take a look at the gap issue, but don't know how to reproduce it, so if you have some dummy data + code that makes this gap it would be easier to test solutions.

[teunbrand]

I'm going to close this issue as I think that the underlying issue is with how graphics devices work, which I don't have a lot of control over from gg4hx's POV.