API for datatypes derived from googlevoxels (github.com/janelia-flyem/dvid/datatype/googlevoxels)
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Command-line:

$ dvid repo <UUID> new googlevoxels <data name> <settings...>

	Adds voxel support using Google BrainMaps API.

	Example:

	$ dvid repo 3f8c new googlevoxels grayscale volumeid=281930192:stanford jwtfile=/foo/myname-319.json

    Arguments:

    UUID           Hexadecimal string with enough characters to uniquely identify a version node.
    data name      Name of data to create, e.g., "mygrayscale"
    settings       Configuration settings in "key=value" format separated by spaces.

    Required Configuration Settings (case-insensitive keys)

    volumeid       The globally unique identifier of the volume within Google BrainMaps API.
    jwtfile        Path to JSON Web Token file downloaded from http://console.developers.google.com.
                   Under the BrainMaps API, visit the Credentials area, create credentials for a
                   service account key, then download that JWT file.

    Optional Configuration Settings (case-insensitive keys)

    tilesize       Default size in pixels along one dimension of square tile.  If unspecified, 512.


$ dvid googlevoxels volumes <jwtfile>

	Contacts Google BrainMaps API and returns the available volume ids for a user identified by a 
	JSON Web Token (JWT) file.

	Example:

	$ dvid googlevoxels volumes /foo/myname-319.json

    Arguments:

    jwtfile        Path to JSON Web Token file downloaded from http://console.developers.google.com.
                   Under the BrainMaps API, visit the Credentials area, create credentials for a
                   service account key, then download that JWT file.


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HTTP API (Level 2 REST):

GET  <api URL>/node/<UUID>/<data name>/help

	Returns data-specific help message.


GET  <api URL>/node/<UUID>/<data name>/info

    Retrieves characteristics of this data in JSON format.

    Example: 

    GET <api URL>/node/3f8c/grayscale/info

    Arguments:

    UUID          Hexadecimal string with enough characters to uniquely identify a version node.
    data name     Name of googlevoxels data.


GET  <api URL>/node/<UUID>/<data name>/tile/<dims>/<scaling>/<tile coord>[?options]

    Retrieves a tile of named data within a version node.  The default tile size is used unless
    the query string "tilesize" is provided.

    Example: 

    GET <api URL>/node/3f8c/grayscale/tile/xy/0/10_10_20

    Arguments:

    UUID          Hexadecimal string with enough characters to uniquely identify a version node.
    data name     Name of data to add.
    dims          The axes of data extraction in form "i_j_k,..."  Example: "0_2" can be XZ.
                    Slice strings ("xy", "xz", or "yz") are also accepted.
    scaling       Value from 0 (original resolution) to N where each step is downres by 2.
    tile coord    The tile coordinate in "x_y_z" format.  See discussion of scaling above.

  	Query-string options:

    tilesize      Size in pixels along one dimension of square tile.
  	noblanks	  If true, any tile request for tiles outside the currently stored extents
  				  will return a placeholder.
    format        "png", "jpeg" (default: "png")
                    jpeg allows lossy quality setting, e.g., "jpeg:80"  (0 <= quality <= 100)
                    png allows compression levels, e.g., "png:7"  (0 <= level <= 9)


GET  <api URL>/node/<UUID>/<data name>/raw/<dims>/<size>/<offset>[/<format>][?queryopts]

    Retrieves either 2d images (PNG by default) or 3d binary data, depending on the dims parameter.  
    The 3d binary data response has "Content-type" set to "application/octet-stream" and is an array of 
    voxel values in ZYX order (X iterates most rapidly).

    Example: 

    GET <api URL>/node/3f8c/segmentation/raw/0_1/512_256/0_0_100/jpg:80

    Returns a raw XY slice (0th and 1st dimensions) with width (x) of 512 voxels and
    height (y) of 256 voxels with offset (0,0,100) in JPG format with quality 80.
    By "raw", we mean that no additional processing is applied based on voxel
    resolutions to make sure the retrieved image has isotropic pixels.
    The example offset assumes the "grayscale" data in version node "3f8c" is 3d.
    The "Content-type" of the HTTP response should agree with the requested format.
    For example, returned PNGs will have "Content-type" of "image/png", and returned
    nD data will be "application/octet-stream". 

    Arguments:

    UUID          Hexadecimal string with enough characters to uniquely identify a version node.
    data name     Name of data to add.
    dims          The axes of data extraction in form "i_j_k,..."  
                    Slice strings ("xy", "xz", or "yz") are also accepted.
                    Example: "0_2" is XZ, and "0_1_2" is a 3d subvolume.
    size          Size in voxels along each dimension specified in <dims>.
    offset        Gives coordinate of first voxel using dimensionality of data.
    format        Valid formats depend on the dimensionality of the request and formats
                    available in server implementation.
                  2D: "png", "jpg" (default: "png")
                    jpg allows lossy quality setting, e.g., "jpg:80"
                  nD: uses default "octet-stream".

    Query-string Options:

    compression   Allows retrieval or submission of 3d data in "raw" (default) or "lz4" format.  
                     The 2d data will ignore this and use the image-based codec.
  	scale         Default is 0.  For scale N, returns an image down-sampled by a factor of 2^N.
    throttle      Only works for 3d data requests.  If "true", makes sure only N compute-intense operation 
    				(all API calls that can be throttled) are handled.  If the server can't initiate the API 
    				call right away, a 503 (Service Unavailable) status code is returned.