Describing a tile

Trying to use the Djatoka jpeg2000 image viewer to display the image tiles / regions served up by an installation of the now-defunct eRez image server underscored the value of a good web API.

eRez Tile API

Parm Name	Type	Function
src	string	path to the ptif src, relative to the eRez image root
width	integer	width of the resulting image tile (will stretch to fit)
height	integer	height of the resulting image tile (will stretch to fit)
top	float	the position of the top edge of the tile relative to the entire scaled image, expressed as a decimal fraction
left	float	see "top"
bottom	float	see "top"
right	float	see "top"
scale	float	the ratio of the dimensions of an entire image composed of tiles in the requested size to the dimensions of the original image, expressed as a decimal fraction.
tmp	string constant	the value is "ajax-viewer", unquoted

OpenURL getRegion API

Parm Name	Type	Function
svc.level	integer	a scaling indicator, as specified here
svc.region	integer or float list	the top edge position, left edge position, region height and width. Concatenated as a comma-delimited value.
svc.scale	integer or float list	scaling factor as either a single value, or a targeted width and height. If the latter, a value of zero for one of the dimensions indicates the original proportions should be maintained.

Translating OpenURL Level to eRez Scale

After calculating the maximum levels, any given level converts to scale as:

scale = 1 / 2(maxLevels - requestedLevel)