SIA xs sia Implementation of an XML Schema describing a Simple Image Access Service. Based on the Simple Image Access Specification by Doug Tody et al. The capabilities of an SIA implementation. The class of image service: Cutout, Mosaic, Atlas, Pointed The maximum image query region size, expressed in decimal degrees. Not providing this element or specifying a value of 360 degrees indicates that there is no limit and the entire data collection (entire sky) can be queried. Not providing a value is the prefered way to indicate that there is no limit. An upper bound on a region of the sky that can be covered by returned images. That is, no image returned by this service will cover more than this limit. Not providing this element or specifying a value of 360 degrees indicates that there is no fundamental limit to the region covered by a returned image. When the imageServiceType is “Cutout” or “Mosaic”, this represents the largest area that can be requested. In this case, the “no limit” value means that all-sky images can be requested. When the type is “Atlas” or “Pointed”, it should be a region that most closely encloses largest images in the archive, and the ”no limit” value means that the archive contains all-sky (or nearly so) images. Not providing a value is the prefered way to indicate that there is no limit. A measure of the largest image the service can produce given as the maximum number of pixels along the first or second axes. Not providing a value indicates that there is no effective limit to the size of the images that can be returned. This is primarily relevant when the imageServiceType is “Cutout” or “Mosaic”, indicating the largest image that can be created. When the imageServiceType is “Atlas” or “Pointed”, this should be specified only when there are static images in the archive that can be searched for but not returned because they are too big. When a service is more fundementally limited by the total number of pixels in the image, this value should be set to the square-root of that number. This number will then represent a lower limit on the maximum length of a side. The maximum image file size in bytes. Not providing a value indicates that there is no effective limit the size of files that can be returned. This is primarily relevant when the imageServiceType is “Cutout” or “Mosaic”, indicating the largest files that can be created. When the imageServiceType is “Atlas” or “Pointed”, this should be specified only when there are static images in the archive that can be searched for but not returned because they are too big. The largest number of records that the Image Query web method will return. Not providing this value means that there is no effective limit. This does not refer to the total number of images in the archive but rather maximum number of records the service is capable of returning. A limit that is greater than the number of images available in the archive is equivalent to their being no effective limit. (See RM, Hanisch 2007.) a set of query parameters that is expected to produce at least one matched record which can be used to test the service. The maximum size in the longitude (R.A.) direction given in degrees The maximum size in the latitude (Dec.) direction given in degrees The sky position in the longitude (R.A.) direction The sky position in the latitude (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. A query to be sent to the service the center position of the rectangular region that should be used as part of the query to the SIA service. the rectangular size of the region that should be used as part of the query to the SIA service. the verbosity level to use where 0 means the bare minimum set of columns and 3 means the full set of available columns. any extra (particularly non-standard) parameters that must be provided (apart from what is part of base URL given by the accessURL element). this value should be in the form of name=value pairs delimited with ampersands (&).