Bug fix to vectaster

[Geary-Layne]

Linear Issue

IDSSE-638

Changes

• The two bugs
  • Not including edge pixels when rasterizing polygons
    • Now after getting 'fill' pixels, also get edge pixels
  • Sometimes pixels were identified more than once when rasterizing polygons
    • Now uses sets
• Other changes
  • Added the ability to create a geo image without background data, helpful for testing
  • Added functionality to ColorPalettes to help scaling color range, helpful for WindGust color palette
  • Added support for passing geojson object as dictionary to some functions
  • Increased test coverage

Explanation

N/A

[mackenzie-grimes-noaa]

No changes needed, just comments to be sure I understand what's happening in this code.

[mackenzie-grimes-noaa]

Just to check for understanding: it looks like we turn the pixel list into a set to prevent duplicates here, but the _pixels_for_line_seg() function we called also turns them into a set before returning them to us.

Is there a reason that _pixels_for_line_seg() isn't guaranteed to return unique pixels, but the similar function _pixels_for_polygon() is? Maybe because Polygons have boundaries + edges so the logic in that function is more complex and complete?

[Geary-Layne]

Putting set around _pixels_for_line_seg() isn't to insure the returned pixels are unique (they are, as are the returned list from three pixels_for...), it is there to cast the returned list to a set, so that when additional pixels are added, they are assured to be unique (notice the pixels.update() below). It might be better to have the return type of all three of these be sets rather than lists, but I'm not sure if there would be any impacts from returning collections, vs sequence. I'll look into this on my next task

[mackenzie-grimes-noaa]

I've never seen this syntax in Python, what does this do? Is it shorthand for looping through all the values in the array and setting them to fill_color?

[Geary-Layne]

It's call the Ellipsis object, I found it in some example code. I originally thought it was just part of numpy but after you comment I looked it up and it is a python thing. In this case it is equivalent to rgb_array[:,:] = fill_color, which sets the third dim equal to fill_color for all of the first 2 dims. So for each pixel location (i,j) set the color to fill_color.