Provider

Transform

This provider allows you to implement a function to change the RGBA value of each individual pixel in imagery from another provider. Like the "Custom" provider this is implemented using Yaegi and requires you to include your own Go code. The interface for this is however much simpler, it requires just a single function:

Description

func transform(r, g, b, a uint8) (uint8, uint8, uint8, uint8)

You can include the logic in a dedicated file, or inline in configuration. No special types or functions are available for use besides the standard library. A package declaration and any imports are optional.

This can only be used with layers that return JPEG or PNG images. The result is always output in PNG format at the same size as the tile from the downstream provider.

Example

YAML
JSON

provider:
  name: transform
  threads: 8
  formula: |
    func transform(r, g, b, a uint8) (uint8, uint8, uint8, uint8) {
      return g,b,r,a
    }
  provider:
    name: proxy
    url: https://tile.openstreetmap.org/{z}/{x}/{y}.png

{
  "provider": {
    "name": "transform",
    "threads": 8,
    "formula": "func transform(r, g, b, a uint8) (uint8, uint8, uint8, uint8) {\n  return g,b,r,a\n}\n",
    "provider": {
      "name": "proxy",
      "url": "https://tile.openstreetmap.org/{z}/{x}/{y}.png"
    }
  }
}

Configuration

Configuration options
Parameter	Description	Type	Required	Default
`file`	An absolute file path to find the Go code implementing the transformation	string	No	None
`formula`	The go code implementing the transformation. Required if file isn’t included	string	No	None
`provider`	The provider to get the imagery to transform	Provider	Yes	None
`threads`	How many threads (goroutines) to use per tile. The typical tile has 65,536 pixels, setting this to 8 for instance means each thread has to process 8,192 pixels in parallel. This helps avoid latency becoming problematically slow.	int	No	1