Rasters

As an alternative to voxels, the map component can store what an adapter ingests as a raster: a 2D image in which each pixel covers a fixed area of the ground. Rasters suit flat environments, such as the occupancy grid produced by a 2D lidar, where they are smaller and cheaper to publish than voxels, and can be viewed and edited as an ordinary image.

There are two raster node types:

• A raster map is a single image.
• A raster tiler divides the image into square tiles, and creates a raster map for each tile as it is needed. Tiles which have not been drawn on take up no space, so a tiler can cover a large area at a fine resolution.

An adapter chooses which it writes using its outputMode setting: "rastermap" or "rastertiler". See Output Settings. Adapters which support rasters are ros.pointcloud2, ros.laser-scan, ros.occupancy-grid, spot and static-pointcloud.

Raster Settings

The image is described by the rasterSettings object of the adapter.

Setting	Type	Description	Default
resolutionX	number	The size of a pixel, in metres, in the X direction. If only one of resolutionX and resolutionY is given the other is set to the same value, giving square pixels. The ros.pointcloud2 and ros.laser-scan adapters require a resolution; ros.occupancy-grid takes it from the grid when it is not given.
resolutionY	number	The size of a pixel, in metres, in the Y direction.
pixelFormat	string	How each pixel is stored. One of "gray8" (one byte per pixel), "gray16" (two bytes per pixel) or "rgba" (four bytes per pixel, with transparency).	"rgba"
imageFormat	string	How the image is encoded. One of "png", "tiff" or "raw". A "raw" image is a plain array of pixels with no header.	"png"
tileWidth	integer	The width of a tile in pixels. Only used by a raster tiler.	512
tileHeight	integer	The height of a tile in pixels. Only used by a raster tiler.	512
unknownColor	colour	The colour reported for areas which no tile covers, and used to fill the gaps when a tiled image is assembled.	Transparent

A colour can be written as a CSS colour string, such as "red", "#ff0000" or "rgba(255, 0, 0, 1)", or as an object: {"r": 255, "g": 0, "b": 0, "a": 255}.

Mapping Settings

The mappingSettings object of the adapter chooses the colours used to draw what the adapter has observed. Each is a colour, as above.

Setting	Description	Default
occupiedColor	The colour of space containing an obstacle.	Green: rgb(0, 200, 0)
unoccupiedColor	The colour of space which is known to be free.	Transparent
unexploredColor	The colour of space which has not been observed. If unknownColor is not set it takes this value, so that areas the robot has not visited look unexplored.	Transparent

Example

"uniqueAdapterName": {
  "enabled": true,
  "type": "ros.laser-scan",
  "settings": {
    "source": "/ros/scan",
    "outputMode": "rastertiler",
    "rasterSettings": {
      "resolutionX": 0.05,
      "pixelFormat": "rgba",
      "tileWidth": 256,
      "tileHeight": 256
    },
    "mappingSettings": {
      "occupiedColor": "black",
      "unexploredColor": "#cccccc"
    }
  }
}

Working with Rasters

The pixels of a raster can be read and changed with the raster services of the dynamic map; see Data Model. Together with the Raster File adapter, which keeps a raster node synchronised with an image file on disk, this allows a map to be drawn in an image editor.