Implementation of an XML Schema describing a Simple Image
Access Service. Based on "The Simple Image Access Specification"
by Doug Tody et al.
Diff 0.01-0.02: The Topologi tool apparently doesn't like
annotations of global elements referenced locally.
Although, this does not appear to be in violation of the XML
Schema standard, they have been commented out for the time
being.
Diff 0.02-0.1: Changed target namespace to
http://www.ivoa.net/xml/prop/VOStdService.
Diff 0.1-0.2: Forgot to put in all-important BaseURL
element in ParamHTTPGet.
Diff 0.3-0.4: Changed name to SIA; moved ParamHTTPGet to VOResource
Diff 0.4-0.5: drop use of "ditem"; updated for changes to
VODataService
The capabilities of an SIA implementation. It includes
the listing of the columns that appear in image query
output VOTable and SIA-specific metadata.
Editor's Notes:
* This is a prototype definition to
illustrate how to extend the schema to a speicific
standard interface.
* Staging information is not included yet.
The largest number of records that the Image Query web
method will return.
The maximum image file size in bytes.
The maximum image query region size, expressed in decimal
degrees. A value of 360 degrees indicates that there is no limit
and the entire data collection (entire sky) can be queried.
The maximum size in the longitude (R.A.) direction
The maximum size in the latitdude (Dec.) direction
The maximum image query region size, expressed in decimal
degrees. A value of 360 degrees indicates that there is no limit
and the entire data collection (entire sky) can be requested.
The maximum size in the longitude (R.A.) direction
The maximum size in the latitdude (Dec.) direction
The largest image (in terms of pixels) that can be requested.
The maximum number of pixels in the longitude (R.A.)
direction
The maximum number of pixels in the latitdude (Dec.)
direction
The class of image service: Cutout, Mosaic, Atlas, Pointed
This is a service which extracts or "cuts out" rectangular
regions of some larger image, returning an image of the
requested size to the client. Such images are usually drawn
from a database or a collection of survey images that cover
some large portion of the sky. To be considered a cutout
service, the returned image should closely approximate (or at
least not exceed) the size of the requested region; however,
a cutout service will not normally resample (rescale or
reproject) the pixel data. A cutout service may mosaic image
segments to cover a large region but is still considered a
cutout service if it does not resample the data. Image
cutout services are fast and avoid image degredation due to
resampling.
This service is similar to the image cutout service
but adds the capability to compute an image of the
size, scale, and projection specified by the
client. Mosaic services include services which
resample and reproject existing image data, as well
as services which generate pixels from some more
fundamental dataset, e.g., a high energy event list
or a radio astronomy measurement set. Image mosaics
can be expensive to generate for large regions but
they make it easier for the client to overlay image
data from different sources. Image mosaicing
services which resample already pixelated data will
degrade the data slightly, unlike the simpler cutout
service which returns the data unchanged.
This category of service provides access to
pre-computed images that make up a survey of some
large portion of the sky. The service, however, is
not capable of dynamically cutting out requested
regions, and the size of atlas images is
predetermined by the survey. Atlas images may range
in size from small cutouts of extended objects to
large calibrated survey data frames.
This category of service provides access to
collections of images of many small, "pointed"
regions of the sky. "Pointed" images normally focus
on specific sources in the sky as opposed to being
part of a sky survey. This type of service usually
applies to instrumental archives from observatories
with guest observer programs (e.g., the HST archive)
and other general purpose image archives (e.g., the
ADIL). If a service provides access to both survey
and pointed images, then it should be considered a
Pointed Image Archive for the purposes of this
specification; if a differentiation between the
types of data is desired the pointed and survey data
collections should be registered as separate image
services.