yourSky[^1]: Rapid Desktop Access to\
Custom Astronomical Image Mosaics

Joseph C. Jacob[^2]^a^, Robert Brunner^b^, David W. Curkendall^a^, S.
George Djorgovski^b^, John C. Good^c^, Laura Husman^a^, George
Kremenek^d^, and Ashish Mahabal^b^

^a^Jet Propulsion Laboratory, California Institute of Technology

^b^Astronomy Department, California Institute of Technology

^c^Infrared Processing and Analysis Center, California Institute of
Technology

^d^San Diego Supercomputer Center

abstract

The yourSky custom astronomical image mosaicking software has a Web
portal architecture that allows access via ordinary desktop computers
with low bandwidth network connections to high performance and highly
customizable mosaicking software deployed in a high performance
computing and communications environment. The emphasis is on custom
access to image mosaics constructed from terabytes of raw image data
stored in remote archives. In this context, custom access refers to new
technology that enables on the fly mosaicking to meet user-specified
criteria for region of the sky to be mosaicked , datasets to be used,
resolution, coordinate system, projection, data type and image format.
The yourSky server is a fully automated end-to-end system that handles
all aspects of the mosaic construction. This includes management of
mosaic requests, determining which input images are required to fulfill
each request, management of a data cache for both input image plates and
output mosaics, retrieval of input image plates from massive remote
archives, image mosaic construction on a multiprocessor system, and
making the result accessible to the user on the desktop. The URL for
yourSky is [http://yourSky.jpl.nasa.gov](http://yourSky.jpl.nasa.gov/).

1.  Astronomical image mosaics, Web portal, Image reprojection, Data
    access.

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1.  introduction

In recent years the Astronomy community has witnessed an explosion in
the size and complexity of datasets that are available for astronomical
research due to rapid advances in remote sensing technology. The massive
datasets that now exist collectively contain tens of terabytes of
imagery and catalog data in wavelengths spanning the entire
electromagnetic spectrum. Although this rich data store represents a
significant opportunity for new scientific discoveries, it also
represents a serious challenge to the community: *How does one
effectively and efficiently extract information from such a large and
complex collection of data?* To address this question, the Astronomy and
Information Technology communities have joined forces to launch the
National Virtual Observatory (NVO) \[1,2,3\] in the United States and
related efforts elsewhere in the world \[4,5,6,7\].

As a community effort, the NVO will necessarily exhibit a loosely
coupled, distributed architecture, with an emphasis on interoperability
between components developed and deployed by domain experts in various
areas. Since many of these components will require an enormous amount of
computation and/or data movement, the NVO will need to be deployed in a
distributed, high performance, scalable computing environment. However,
a significant fraction of astronomical research is conducted by
scientists and students with limited resources, ordinary desktop
computers and low bandwidth network connections. Therefore, to be
effective the NVO will also need to provide portals to its high
performance infrastructure that will make it usable by researchers
anywhere. This paper summarizes some of our early efforts to design,
develop and deploy a useful service called yourSky, for custom
astronomical image mosaicking, with an architecture that supports both
high performance computations and lightweight portals, and matches the
loosely coupled, distributed nature of the NVO infrastructure.

In this paper, mosaicking refers to reprojecting input image plates to a
common coordinate system, projection, equinox and epoch, and combining
the resulting plates to produce a single output image. There are strong
science drivers for mosaicking. The most obvious is that large image
mosaics enable analysis of celestial objects that either do not fit on a
single image plate in the native image partitioning scheme used by a
survey, or fall at the boundary between two or more neighboring plates.
Also, mosaics enable analysis of the large-scale structure of the
universe. In addition, mosaicking datasets in different wavelengths or
from different surveys to the same grid enables multi-spectral analysis,
which could be essential for identifying new, previously unknown, types
of objects, or for identifying new objects that are so faint in a single
wavelength that they are overlooked until combined with the signals from
other wavelengths.

The only client software required to use the yourSky custom astronomical
image mosaic server is the ubiquitous web browser. By filling out and
submitting the form at http://yourSky.jpl.nasa.gov, users have custom
access on their desktop to all of the publicly released data from the
member surveys. In this context, "custom access" refers to new
technology that enables on-the-fly astronomical image mosaicking to meet
user-specified criteria for region of the sky to be mosaicked, dataset
to be used, resolution, coordinate system, projection, data type, and
image format. All mosaic requests are fulfilled from the original
archive data so that the domain experts maintain control and
responsibility for their data and data corruption due to resampling is
minimized because only one reprojection is done from the raw input data.
Currently the data archives that are accessible with yourSky are the
Digitized Palomar Observatory Sky Survey (DPOSS) \[8,9\] and the Two
Micron All Sky Survey (2MASS) \[10\]. DPOSS has captured the entire
northern Sky at 1 arc second resolution in three visible wavelengths.
2MASS has captured the entire sky at 1 arc second resolution in three
infrared wavelengths. The yourSky architecture supports expansion to
include other surveys, without regard to the native image partitioning
scheme used by a particular survey.

The overall architecture for yourSky is described in Section 2, followed
by more detail about the components of yourSky in later sections. These
components include the custom astronomical image mosaicking software
described in Section 3, the request management system described in
Section 4, the plate coverage database described in Section 5, and the
management of local data caches described in Section 6. The member
archives that are accessible with yourSky are described in Section 7.
Finally, a summary and description of our future plans for yourSky are
provided in Section 8.

2.  architecture

The overall architecture for yourSky is illustrated in Figure 1. In the
figure, the numbered descriptions on some of the arrows give the steps
taken to fulfill a typical mosaic request. The procedure is as follows.
The clients at the top left of the illustration are the Web browsers
that may be used to submit requests to yourSky. A simple HTML form
interface, shown in Figure 2, is used to specify the parameters that are
to be passed to the custom astronomical image mosaicking software. The
mosaicking software and the mosaic parameters are described in detail in
Section 3. The yourSky Mosaic Request Manager running on the yourSky
server checks for mosaic requests and hands them off to the Mosaic
Request Handler, using the user priority scheme described in Section 4.
The Mosaic Request Handler queries the Plate Coverage Database,
described in Section 5, to determine which input image plates from DPOSS
or 2MASS are required to fulfill the mosaic request. A fixed size data
cache is maintained on the yourSky server to store the input image
plates required to build recent mosaic requests. If all of the required
input image plates are already present locally in the data cache, the
mosaic is constructed immediately using the custom astronomical image
mosaicking software, described in Section 3. Currently the mosaic
processing is performed on an SGI Poweronyx with eight R10000 processors
running at 194 MHz, but this machine is quite outdated and will need to
be updated in the near future. If some of the required input image
plates are not already cached locally, they need to be retrieved from
their respective archives. Therefore a "tape request" is issued. The
yourSky Tape Request Manager checks for tape requests and hands them off
to the Tape Request Handler, which retrieves the required input image
plates from the appropriate remote archive. Once all of the input image
plates for a request have been cached on a local disk, the custom
astronomical image mosaicking software is launched to construct the
mosaic. When the mosaic, built precisely to match the user's request
parameters, is ready an email is sent back to the user with the URL
where the image mosaic can be downloaded.

3.  Custom Astronomical image Mosaicking Software

The heart of the yourSky server is the custom astronomical image
mosaicking software that is used to construct an image mosaic precisely
matching user-specified parameters. The inputs to the mosaicking
software are a list of input images to be mosaicked and the custom
parameters that determine the properties of the mosaic to be
constructed. The only requirements on the input images are the
following. First, they must comply with the standard dictated by the
Flexible Image Transport System (FITS), a data format that is well
understood by the astronomy community and has long been used as the de
facto method for sharing data within the community \[11\]. FITS format
images encapsulate the image data with keyword-value pairs that give
additional information about how the data values in the image map to
locations on the sky. The second requirement for input images to the
mosaicking software is that the FITS header must contain valid World
Coordinate System (WCS) information. The WCS defines pixel-to-sky and
sky-to-pixel coordinate transformations for a variety of coordinate
systems and projections commonly used by the astronomy community \[12\].

1.  Custom Access

With yourSky, the emphasis is on custom access to astronomical image
mosaics. The following parameters may be used to specify the mosaic to
be constructed:

1.  **Center right ascension and declination:** Required parameters,
    analogous to the CRVAL1 and CRVAL2 FITS keywords, which specify the
    location on the celestial sphere of the tangent point for the image
    projection plane. By default, this center of projection is placed at
    the center pixel in the mosaic, analogous to the CRPIX1 and CRPIX2
    FITS keywords.

2.  **Resolution:** Required parameter(s), analogous to the CDELT1 and
    CDELT2 FITS keywords, which specify the pixel size in degrees in
    each of the two image dimensions *at the mosaic center of
    projection*.

3.  **Radius in degrees:** Optional parameter that limits the mosaic
    size using degrees from the mosaic center. If not specified, the
    radius is determined automatically from the region of coverage of
    the input image
    plates.![](media/image3.png){width="6.533333333333333in"
    height="5.013194444444444in"}

4.  **Width and height in pixels:** Optional parameters, analogous to
    the NAXIS1 and NAXIS2 FITS keywords, that limit the mosaic size
    using a specific number of pixels. These parameters supersede the
    radius in degrees if that is given as well. If not specified, the
    radius is determined automatically from the region of coverage of
    the input image plates.

5.  **Coordinate system:** Required parameter, analogous to the first
    half of the CTYPE1 and CTYPE2 FITS keyword values, that specifies
    the alignment of the mosaic axes in 3-D space. Four coordinate
    systems are supported:

    -   Galactic.

    -   Ecliptic.

    -   J2000 Equatorial.

    -   B1950 Equatorial.

6.  **Projection:** Required parameter, analogous to the second half of
    the CTYPE1 and CTYPE2 FITS keyword values, that specifies how
    locations on the celestial sphere are mapped to the image projection
    plane. All of the projections specified by WCS are supported:

    -   Linear (LIN).

    -   Gnomonic or Tangent Plane (TAN).

    -   Orthographic/Synthesis (SIN).

    -   Stereographic (STG).

    -   Zenithal/Azimuthal Perspective (AZP).

    -   Zenithal/Azimuthal Equidistant (ARC).

    -   Zenithal/Azimuthal Polynomial (ZPN).

    -   Zenithal/Azimuthal Equal Area (ZEA).

    -   Airy (AIR).

    -   Cylindrical Perspective (CYP).

    -   Cartesian (CAR).

    -   Mercator (MER).

    -   Cylindrical Equal Area (CEA).

    -   Conic Perspective (COP).

    -   Conic Equidistant (COD).

    -   Conic Equal Area (COE).

    -   Conic Orthomorphic (COO).

    -   Bonne (BON).

    -   Polyconic (PCO).

    -   Sanson-Flamsteed Sinusoidal (SFL).

    -   Parabolic (PAR).

    -   Hammer-Aitoff (AIT).

    -   Mollweide (MOL).

    -   COBE Quadrilateralized Spherical Cube (CSC).

    -   Quadrilateralized Spherical Cube (QSC).

    -   Tangential Spherical Cube (TSC).

    -   Digitized Sky Survey Plate Solution (DSS).

    -   Plate fit polynomials (PLT).

7.  **Image Format:** Required parameter that specifies the output
    mosaic image format (FITS is recommended but not required). The
    following image formats are currently supported:

    -   FITS.

    -   JPEG.

    -   PGM.

    -   PNG.

    -   TIFF.

    -   Raw Data.

8.  **Data Type:** Required parameter that specifies the data type of
    the mosaic pixels. This is analogous to the BITPIX FITS keyword, but
    for the Raw Data image format some additional data types are
    provided that are not supported by FITS. The following data types
    are supported:

    -   8-bit unsigned integer.

    -   8-bit signed integer (not supported by FITS).

    -   16-bit unsigned integer (not supported by FITS).

    -   16-bit signed integer.

    -   32-bit unsigned integer (not supported by FITS).

    -   32-bit signed integer.

    -   Single precision floating point.

    -   Double precision floating point.

9.  **Quantization Extrema:** Optional parameters that specify the
    minimum and maximum over which to stretch the input pixel values for
    those data types that require quantization to a limited number of
    output bits per pixel (especially, 8-bit and 16-bit integers). The
    user can specify these values to control how many gray levels in the
    output mosaic are assigned to low or high intensity regions of the
    sky.

10. **Pixel Masks:** Optional masks may be specified to discard pixels
    around the outer perimeter or from particular rectangular regions in
    each input image.![](media/image4.wmf){width="6.282638888888889in"
    height="2.7569444444444446in"}

11. **Background Matching:** Logical parameter that specifies whether or
    not yourSky should attempt to match the background intensities among
    the input images that comprise a mosaic in an attempt to produce a
    mosaic that is as seamless as possible.

    1.  Parallel Mosaicking Algorithm

The yourSky mosaicking algorithm is designed to be able to handle
arbitrarily large mosaic requests from typical small requests covering a
single celestial object to all-sky mosaics at full resolution. Also, the
algorithm is efficient in the face of arbitrarily sized input image
plates, so that yourSky can be extended to support other image archives
without consideration of the native image partitioning scheme used by
the archive. For example, the two surveys currently accessible by
yourSky have drastically different native image partitioning schemes,
from millions of small 2 MB image plates in the case of 2MASS to
thousands of much larger 1 GB plates in the case of DPOSS. In addition,
the mosaicking algorithm is designed to support arbitrary mappings from
input image pixels to output mosaic pixels.

The mosaicking proceeds in two phases, *Analysis* and *Build*. During
Analysis, the following is accomplished. First, the mosaic width and
height are determined if they are not provided explicitly as part of the
user-specified parameter set. Second, the pixel coordinates that
intersect the mosaic are determined for each input image along with the
corresponding intersection coordinates from the mosaic. These
coordinates are used to set loop bounds and buffer sizes during the
Build phase. Third, in cases where the data type requires quantization
to a limited number of output bits per pixel in the output mosaic (e.g.
8-bit and 16-bit integers), the minimum and maximum over which the pixel
values should be quantized are determined if these extrema are not
specified explicitly as part of the user-specified parameter set.
Fourth, if background matching is to be done, the intensity correction
for each input image plate is determined.

During the Build phase the information gathered during Analysis is used
to construct the custom mosaic. If the mosaic is to be lower resolution
than the input image plates, the outer loop is over the input image
pixels and the mosaic pixel values are calculated as the average of the
input pixels for which the pixel center falls within the mosaic pixel
region of coverage. If the mosaic is to be roughly the same or higher
resolution than the input image plates, the outer loop is over the
mosaic pixels and the mosaic pixel values are computed to be the result
of sampling from the input images using bilinear interpolation. In
either case, mapping from input pixel coordinates to output pixel
coordinates is done by first mapping from input pixels to a location on
the sky, then mapping from the sky coordinates to the output pixel
coordinates, as illustrated in Figure 3.

The mosaicking proceeds in parallel during both Analysis and Build, with
each processor being assigned a subset of the input image pixels. By
default the input images are assigned to processors in a round robin
fashion, with one processor per image, but the user can reconfigure this
at run-time by specifying the number of processors to be assigned to
each input image. Assigning multiple processors to each input image
plate dramatically improves efficiency for archives, such as DPOSS, that
have such large image plates that only a single or a few input image
plates are required for a typical mosaic request. If multiple processors
are assigned to each input image, a group synchronization among the
processors assigned to the same image is required for each image so that
Analysis results can be accumulated and shared. Also, in all cases, a
global synchronization is required between the Analysis and Build phases
so that Analysis results that relate to the entire mosaic, such as pixel
value distributions required to calculate the appropriate quantization
extrema, can be accumulated and shared. The software should be portable
because it is written in ANSI C and all inter-processor communication
and synchronization is done using Message Passing Interface (MPI), which
has been implemented on many platforms
\[13\].![](media/image5.wmf){width="6.544444444444444in"
height="3.1569444444444446in"}![](media/image6.jpeg){width="6.0in"
height="3.0in"}

2.  Sample Mosaics

Some sample image mosaics[^3], constructed with the yourSky custom image
mosaicking software, are shown in Figures 4, 5 and 6. Figure 4 shows a
full resolution, all-sky, 90 arc second resolution, 14,400 x 7,200 pixel
mosaic constructed from 430 Infrared Astronomical Satellite (IRAS)
\[14\] image plates in each of 4 wavelengths, 12, 25, 60, and 100
microns. High performance exploration of this and other large datasets
is possible using visualization software developed previously at JPL
\[15,16\]. Figure 5 shows a center of the galaxy mosaic from the 2MASS H
band before and after background matching is performed. The striped
appearance without background matching is primarily due to atmospheric
effects that become more pronounced as the path length through the
atmosphere gets longer at different look angles. The background matching
algorithm used by yourSky results in a more seamless mosaic, but edge
effects are still visible. This background matching algorithm will be
improved under a NASA Grand Challenge effort to develop high performance
cornerstone technologies for the NVO. This effort, called Montage, has
staged code improvement deliverables with the final deliverable
scheduled for January, 2005 \[17\]. Figure 6 shows a DPOSS F band mosaic
of M31 in a Galactic Tangent Plane projection. The mosaic shown in the
figure is the center part of a larger 34,816 x 36,352 single precision
floating point mosaic constructed from 9 DPOSS plates at full 1 arc
second resolution.![](media/image7.jpeg){width="4.0in" height="4.0in"}

3.  Performance Results

In this section we show timing results for the yourSky mosaicking
software running on a SGI Origin 2000 with 300 MHz R12000 processors and
512 MB of RAM per processor. The first test mosaic is a 2 x 2 degree
2MASS mosaic of the galactic center at full one arc second resolution.
The resulting mosaic is 7,201 x 7,201 single precision floating point
pixels (207 MB) in size in a Galactic Tangent Plane projection,
constructed from 174 2MASS plates totaling 365 MB in size. The second
test mosaic is a 2 x 2 degree DPOSS mosaic of M31 at 10 arc seconds
resolution, resulting in a 721 x 721 single precision floating point
mosaic in the Galactic Tangent Plane projection. This 2.1 MB mosaic was
constructed from 2 DPOSS plates (total size 2.2 GB). No background
matching was performed for this test. Figure 7 shows the wall clock time
required to construct the mosaics on different numbers of processors on
the Origin 2000. For the 2MASS mosaic, one processor was assigned to
each input image plate, but all the processors were assigned to each
input image plate for DPOSS. The plot shows the scaling curves for up to
64 processors.

4.  Request management![](media/image8.png){width="6.48125in"
    height="4.010416666666667in"}

Simultaneous mosaic requests are accepted from a simple HTML form
submitted from the yourSky mosaic request web page at
[http://yourSky.jpl.nasa.gov](http://yourSky.jpl.nasa.gov/), and queued
on the yourSky server by a Common Gateway Interface (CGI) program
interfacing with the Apache web server. The mosaic parameters for each
request are stored on the yourSky server along with the identity of the
user that submitted the request. The yourSky Mosaic Request Manager,
shown in the architecture diagram in Figure 1, needs to locate these
mosaic requests and assign them one at a time to the Mosaic Request
Handler. A user priority scheme is in place that starts off all users
with equal priority. As requests are processed the user priorities
change based on the number of mosaic pixels produced by each user in the
past period referred to as the Priority Window, currently set to 24
hours. Users with the least number of mosaic pixels produced in the
Priority Window period have highest priority for future mosaic requests.
Furthermore, a mosaic request in progress that has had to wait for input
image plate retrieval from a tape archive gets the highest priority to
run next once all of the required input images have been retrieved. This
ensures that all users get a chance to have their mosaic constructed and
no single user will dominate all the available resources.

5.  Plate coverage database

In order to be accessible by yourSky, all member surveys have to be
included in the Plate Coverage Database that contains the minima and
maxima of the longitudes (right ascensions) and latitudes (declinations)
in each of the supported coordinate systems for all of the input image
plates. The yourSky Mosaic Request Handler queries this database to
determine which input image plates are needed to fulfill each mosaic
request. The open source database, MySQL, is used to store this plate
coverage information \[18,19\]. The result of the query to the Plate
Coverage Database is a list of the input image plates that are required
to fulfill the mosaic request. These input image plates are retrieved
from the appropriate tape archives, staged in a local data cache, and
provided as an input to the image mosaicking software described in
Section 3. The plate coverage database is also accessible as a
standalone service, called the yourSky Archive Database Query, at
<http://yourSky.jpl.nasa.gov/query/index.html>.

6.  Data Management

A data management scheme is implemented on the yourSky server to manage
both a data cache for the input image plates used to fulfill recent
mosaic requests and a work area used to store recently constructed
mosaics until they are downloaded.

The input data cache is maintained at a fixed size with image plates
discarded on a least recently used basis. This enables mosaics to be
recomputed with some changes to the custom request parameters without
having to repeat the input image plate retrieval from the tape archives
if the new request is resubmitted shortly after the original request.
Also, mosaics of popular regions of the sky are likely to have their
input image plates already cached on the yourSky server from previous
requests, so they can be constructed more quickly.

Mosaics that have been completed are stored in a work area from where
the appropriate users may download them. Currently mosaics are purged
after a 24 hour period expires.

7.  Data Archive ACCESS

All of the publicly released data from two archives are currently
accessible by yourSky, the Digitized Palomar Observatory Sky Survey
(DPOSS) and the Two Micron All Sky Survey (2MASS).

DPOSS has captured nearly the entire northern sky at 1 arc second
resolution in three wavelengths, 480 nm (J Band - blue), 650 nm (F
Band - red), and 850 nm (N Band -- near-infrared). The survey data were
captured on photographic plates by the 48" Oschin Telescope at the
Palomar Observatory in California \[8,9\]. The total size of the DPOSS
data accessible by yourSky is roughly 3 TB, stored in over 2,600
overlapping image plates on the High Performance Storage System (HPSS)
\[20\] at the Center for Advanced Computing Research (CACR) at the
California Institute of Technology. The DPOSS plates are each about 1 GB
in size and contain 23,552 x 23,552 pixels covering a roughly 6.5 x 6.5
degree region of the sky. The yourSky server uses a client program
called the Hierarchical Storage Interface (HSI) to retrieve selected
DPOSS plates in batch mode from the HPSS \[21\].

2MASS has captured nearly the entire sky at 1 arc second resolution in
three near-infrared wavelengths, 1.25 μm (J Band), 1.65 μm (H Band), and
2.17 μm (K~S~ Band). The survey data were captured using two 1.3 meter
telescopes, one at Mt. Hopkins, AZ and one at the Cerro Tololo
Inter-American Observatory (CTIO) in Chile \[10\]. The 2MASS archives
contain roughly 10 TB of images and the subset that has been publicly
released to date, nearly 4 TB, is fully accessible by yourSky. This 4 TB
of data is stored in about 1.8 million overlapping plates managed by the
Storage Resource Broker (SRB) at the San Diego Supercomputer Center
(SDSC). Each 2MASS plate is about 2 MB in size and contains 512 x 1,024
pixels covering a roughly 0.15 x 0.30 degree region of the sky. The SRB
is a scalable client-server system that provides a uniform interface for
connecting to heterogeneous data resources, transparently manages
replicas of data collections, and organizes data into "containers" for
efficient access \[22\]. The yourSky server uses a set of client
programs called SRB Tools to access selected 2MASS plates in batch mode
from the SRB.

8.  Conclusion

The yourSky architecture and software for desktop access to custom
astronomical image mosaics has been presented. The architecture of
yourSky allows it to exploit high performance computing resources,
supercomputers and high bandwidth networks, on the server side. However,
at the same time it is widely usable from virtually anywhere because the
architecture also supports very lightweight computing resources on the
client side, e.g., ordinary desktop computers with low bandwidth network
connections. Since the user interface to yourSky is a simple HTML form
submitted at
[http://yourSky.jpl.nasa.gov](http://yourSky.jpl.nasa.gov/), the only
client software required to use yourSky is the ubiquitous web browser,
which most of the potential users probably already has and knows how to
use. This combination of being deployed in a high performance computing
and communications environment while allowing access through simple
portals running on the desktop makes yourSky a good match for the
loosely coupled, distributed architecture of the National Virtual
Observatory (NVO).

The yourSky software includes subsystems for: (i) construction of the
image mosaics on multiprocessor systems, (ii) managing simultaneous user
requests, (iii) determining which image plates from member surveys are
required to fulfill a given request, (iv) caching input image plates and
the output mosaics between requests, and (v) retrieving input image
plates from remote archives. The parallel image mosaicking software
emphasizes custom access to mosaics, allowing the user to specify
parameters that describe the mosaic to be built, including datasets to
be used, location on the sky, size of the mosaic, resolution, coordinate
system, projection, data type, and image format. Performance results
indicate that the yourSky mosaicking software scales well on up to 64
processors, the largest size partition available on the SGI Origin 2000
at the Jet Propulsion Laboratory.

A number of current and future efforts are planned to extend the
capabilities of yourSky. First, a graphical front end to yourSky is
under construction that will allow web-based pan and zoom over a medium
resolution, all sky representation of each dataset, along with the
capability of plotting symbol overlays from catalogs on top of the
imagery. This browse mode for yourSky will be interoperable with the
existing yourSky server so that it can be used to help formulate mosaic
requests to yourSky. Another effort underway is to modify yourSky so
that the mosaicking code is run on computational grids, such as NASA's
Information Power Grid (IPG) \[23\] or NSF's TeraGrid \[24\], rather
than on a local server. The collective computational power of the
existing Grid infrastructure far exceeds that of any local server so
this would enable handling of much larger or more numerous mosaic
requests. Finally, yourSky serves as a pathfinder for the Montage
project \[17\], which is sponsored by the NASA Earth Science Technology
Office (ESTO) -- Computational Technologies (CT) Project as a Grand
Challenge effort. Montage will extend yourSky capabilities in the
following ways: (i) science quality will be improved by ensuring flux
per area is preserved in the output mosaics; (ii) performance will be
improved to meet aggressive throughput milestones; (iii) Montage will be
made fully interoperable with the NVO infrastructure, including
interoperability with other archives, analysis and visualization tools,
and use of any data format standards adopted by the NVO; and (iv)
Montage will be fully interoperable with the grid infrastructure being
established by the TeraGrid. Montage has staged code improvement
deliverables with the final deliverable scheduled for January, 2005.

acknowledgements

This research was sponsored by the Space Science Applications of
Information Technology (SAIT) Program, Office of Space Science, National
Aeronautics and Space Administration (NASA). S.G.D., R.B., and A.M.
acknowledge a partial support from the NASA Applied Information Systems
Research Program (AISRP). Processing of DPOSS was supported in part by a
generous grant from the Norris Foundation and other private donors.
Atlas images obtained as part of the Two Micron All Sky Survey (2MASS),
a joint project of the University of Massachusetts and the Infrared
Processing and Analysis Center/California Institute of Technology,
funded by NASA and the National Science Foundation.

This research was carried out at the Jet Propulsion Laboratory,
California Institute of Technology, under a contract with the National
Aeronautics and Space Administration. Reference herein to any specific
commercial product, process, or service by trade name, trademark,
manufacturer, or otherwise, does not constitute or imply its endorsement
by the United States Government or the Jet Propulsion Laboratory,
California Institute of Technology.

references

1.  The National Virtual Observatory (USA),
    [http://us-vo.org](http://us-vo.org/).

2.  National Virtual Observatory Science Definition Team Report:
    *Towards the National Virtual Observatory*, April, 2002,
    [http://nvosdt.org](http://nvosdt.org/).

3.  NVO White Paper: *Toward a National Virtual Observatory: Science
    Goals, Technical Challenges, and Implementation Plan*, in Virtual
    Observatories of the Future, R.J. Brunner, S.G. Djorgovski, and A.S.
    Szalay, eds., Astronomical Society of the Pacific Conference Series,
    Vol. 225, pp. 353-372, 2001. Also avaliable online at
    <http://www.arxiv.org/abs/astro-ph/0108115> and at
    [http://nvosdt.org](http://nvosdt.org/).

4.  The AstroGrid (UK),
    [http://www.astrogrid.org](http://www.astrogrid.org/).

5.  The Astrophysical Virtual Observatory (Europe),
    <http://www.eso.org/avo>.

6.  The Australian Virtual Observatory (Australia),
    <http://www.atnf.csiro.au/people/rnorris/AVO>.

7.  The Virtual Observatory -- India,
    <http://vo.iucaa.ernet.in/~voi/html/homepage.html>.

8.  S.G. Djorgovski, R.R. Gal, S.C. Odewahn, R.R. de Carvalho, R.
    Brunner, G. Longo, and R. Scaramella, *The Palomar Digital Sky
    Survey (DPOSS)*, <http://www.arXiv.org/abs/astro-ph/9809187>.

9.  The Digitized Palomar Observatory Sky Survey (DPOSS),
    <http://www.astro.caltech.edu/~george/dposs>.

10. The Two Micron All Sky Survey (2MASS),
    <http://www.ipac.caltech.edu/2mass>.

11. The Flexible Image Transport System (FITS),
    [http://fits.gsfc.nasa.gov](http://fits.gsfc.nasa.gov/),
    <http://www.cv.nrao.edu/fits>.

12. E.W. Greisen and M. Calabretta, *Representation of Celestial
    Coordinates In FITS*,
    <http://www.atnf.csiro.au/people/mcalabre/WCS.htm>.

13. MPI, The Message Passing Interface Standard,
    <http://www-unix.mcs.anl.gov/mpi>.

14. The Infrared Astronomical Satellite (IRAS),
    <http://www.ipac.caltech.edu/ipac/iras/iras.html>.

15. J.C. Jacob and L. Plesea, *Fusion, Visualization and Analysis
    Framework for Large, Distributed Datasets*, IEEE Aerospace
    Conference, 2001, ISBN 0-7803-6600-X.

16. J.C. Jacob and L.E. Husman, *Large Scale Visualization of Digital
    Sky Surveys*, Virtual Observatories of the Future, R.J. Brunner,
    S.G. Djorgovski, and A.S. Szalay, eds., Astronomical Society of the
    Pacific Conference Series, Vol. 225, pp. 291-296, 2001.

17. Montage: High Performance Cornerstone Technologies for the National
    Virtual Observatory,
    [http://montage.ipac.caltech.edu](http://montage.ipac.caltech.edu/).

18. M. Widenius, MySQL AB, D. Axmark, *MySQL Reference Manual:
    Documentation from the Source*, O'Reilly, June, 2002, ISBN
    0-59600-265-3.

19. MySQL, [http://www.mysql.com](http://www.mysql.com/).

20. The High Performance Storage System (HPSS) at Caltech's Center for
    Advanced Computing Research,
    <http://www.cacr.caltech.edu/resources/HPSS/index.html>.

21. Hierarchical Storage Interface (HSI) for High Performance Storage
    Systems (HPSS), <http://www.sdsc.edu/Storage/hsi>.

22. The Storage Resource Broker (SRB) at San Diego Supercomputer Center
    (SDSC), <http://www.npaci.edu/SRB>.

23. The Information Power Grid (IPG),
    [http://www.ipg.nasa.gov](http://www.ipg.nasa.gov/).

24. The TeraGrid, [http://www.teragrid.org](http://www.teragrid.org/).

[^1]: <http://yourSky.jpl.nasa.gov/>

[^2]: <Joseph.Jacob@jpl.nasa.gov>; phone 1 818 354-0673; fax 1 818
    393-6141; <http://pat.jpl.nasa.gov/public/jjacob>; Jet Propulsion
    Laboratory, 4800 Oak Grove Drive, Mail Stop 126-104, Pasadena, CA
    91109-8099

[^3]: The input data used to construct these mosaics was provided
    courtesy of the respective archives, but the images shown here are
    derived products, constructed by yourSky, and as such have not been
    endorsed by the respective archives, should not be expected to be
    suitable for all scientific purposes, and should not be taken to be
    indicative of the image quality of the raw data provided by the
    respective archives.