48 September 2007 | GEOconnexion International Magazine

ALISTAIR MACLENAN LOOKS AT HOWLIZARDTECH’S COMPRESSIONTECHNOLOGY HELPS THE STATE ARCHIVEOF ROME TO PRESERVE AND PUBLISHTHOUSANDS OF HISTORIC MAPS

HISTORIC MAP PRESERVATIONTHE DIGITAL WAY

The State Archive of Rome (ASRoma), established in 1871, housesand preserves tens of thousands of historical maps, registries, andother documents produced in centuries past and relating to theregion around Rome and the Papal State. They range in physicalsize from very small drawings to roll maps several meters in length.The Archive provides access to these documents and search aidsand other services to researchers of Italian history. However, even inthe age of scanning technologies the lack of an efficient means ofdistributing visual reproductions of these documents has limitedtheir usefulness to the 30-plus daily visitors to its reading room inBorromini’s celebrated Palazzo della Sapienza. Multi-resolutionimage formats and Web-server optimizing software has emerged asthe solution for capturing once and for all the full-color detail ofthese maps and other documents and preserving the originals insafe archival storage.

The Quest for Balance In the 1950s ASRoma launched a massive effort to put the mostprecious and most often consulted documents on microfilm, whichwould enable the Archive to better preserve the originals whilemaking it possible for researchers to view this treasured culturalheritage. At the time, this was the best balance between access andpreservation, the twin mission of archiving.

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Over the years many of the documentswere also photographed, both so thatauthors could publish images from thecollection in articles and books and so thatthe Archive’s visitors could take awayprinted copies. A reprographic service wasadded early on to facilitate these processes,though digital reprographics service for theArchive was only developed in 1997.

While traditional photography andmicrofilm aided in preservation, they didlittle to help in providing access. Microfilmuse was tied to the viewers on site andphotograph copies, while portable, wereneither quick nor cheap. Furthermore, large-format documents were not even able to beadequately captured on film so that theiroriginals could be preserved.

The Problem of Management andDistributionIn 1997 ASRoma initiated the Imago IIproject, in which a significant initial digitalasset was produced by scanning 130,000 ofthe most precious and most consulted ofthe Archive’s documents, approximately15,000 of them maps. The goal of Imago IIwas to better preserve the originaldocuments while at the same time broaden-ing access to them through publishing onthe Internet. As scanners and digital backsbecame more prevalent and their technolo-gy improved it was finally possible to createdigital TIFFs of the large-format maps at 250-300 DPI, a printable resolution.

At this point, management and distribu-tion of digital files became the mostproblematic issue facing the Archive. Theelectronic files that resulted from thescanning process were much too large forWeb distribution. At resolutions suitable fordetailed viewing and printing, even thesmallest documents would be unacceptably

slow to download for Web users, and thelarge-format documents would remaininaccessible once again.

Many digital libraries at the time used aprocess in which TIFF masters of their imagefiles were converted to lower-resolutionJPEG files that could be more efficientlydistributed over the Internet, but this

50 September 2007 | GEOconnexion International Magazine

solution to the problem came at theexpense of visual detail and printability.ASRoma’s administrators had heard aboutthe success the American Memory projecthad had using a multi-resolution imagetechnology from LizardTech on maps in thecollections of the United States Library ofCongress.

Assembling the SolutionAs the second phase in the Imago II projectstarting in 2000, ASRoma, supported byLizardTech’s Italian Reseller, Sysdeco Italia,provided users worldwide with access tofull-resolution imagery via the Web byconverting all of its imagery from TIFF toLizardTech’s MrSID format using LizardTech’sGeoExpress image manipulation andencoding software.

MrSID is a dynamic image technologyand format whose name is an acronym for“multi-resolution seamless image database”,which simply means that users may zoom inand choose any subregion of an image atany desired resolution or “zoom level” andthat portion of the image will be extractedand sent to them, either as a JPEG or asMrSID data. By transforming image datafrom “pixel space” to “wavelet coefficient”space and reordering the bits, the MrSIDtechnology is able to reduce the size ofimage files by about half. This reduction,known as “lossless compression”, is madebefore any data is discarded. The encodingprocess creates multiple resolutions of an

The United Kingdom Hydrographic Office (UKHO) is pleased to announce that it has been contracted by the Military Survey Department (MSD) of the United Arab Emirates (UAE) to advise on the planning and management of the Hydrographic Survey of their Territorial Waters.

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The closing date for submitting the PQQ will be at 12:00 on Friday 12th October 2007.

United Arab Emirates- Hydrographic Survey

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image within one “single-source” image file,so that space-intensive image pyramids areobviated, image updates can be managedmore efficiently, and users can extract anyview at any zoom level very quickly.

The MrSID imagery was used incombination with a Web-interactiveapplication integrating LizardTech’s ExpressServer image delivery software for fastonline image viewing at full resolution.Express Server is server add-on softwarethat enables common Web servers todistribute raster images much more quicklyby taking advantage of inherent efficienciesin wavelet-based formats such as MrSID andJPEG 2000. Dott. Paulo Buonora of ASRomasaid that the project would never havereached success without LizardTech’sproducts.

Integration and InteroperabilityIn 2005, ASRoma began to add the originalroll maps from the Gregoriano Cadastre,some of which measure three to fourmeters in length, to the digital collection.The Archive scanned them directly to MrSIDformat using a special camera (Metis DMC)whose sensor moves internally to put threescans in a single image file. The GregorianoCadastre, commissioned in 1816 by PopePio VII, was carried out and finished in 1835by Pope Gregorio. It was the first geometriccadastre of the Papal State. At 256 DPI,some of these image files were larger than 3GB, and there were 4000 of them. So far

about ten percent of them have beenscanned.

Because it was desirable to have itsdigital image assets in a non-proprietary,ISO standard format, the Archive finallyconverted all of its MrSID images to the ISOstandard JPEG 2000 format at a compres-sion ratio of 20:1 – again using GeoExpress– then catalogued them for efficient onlinepublishing via Express Server. This was thethird and final phase of the project.Conversion to JPEG 2000 means not onlythat the Archive’s library of imagery will besafely stored in a non-proprietary, ISOstandard format for the future, but also thatmaps from the collection can be georefer-enced and then integrated into geographicinformation systems (GIS) to form part ofthe emerging international and interdiscipli-nary “Geospatial Web”. The Archive is nowdeveloping a georeferencing program for itsJPEG 2000 imagery.

BenefitsThe result of the Imago II project is an easilyaccessed online catalog of more than130,000 maps and other documents.Researchers anywhere in the world can nowaccess these pages of Rome’s historywithout having to travel there, and theimagery distributed online is print quality,with all the visual detail of the originalworks. This collection has also been joinedwith other similar archives from othercultural institutes, where they are all made

available as a single digital archive throughthe Center for Preservation Digital Library(www.cflr.beniculturali.it).

The Archive’s user base has alsochanged as a result of the project; whereasit was previously made up of the fewspecialists whose occupations gave themsufficient motivation to make the journey tothe reading room in Rome from far-flunglocations around the globe, it now includesthousands of ordinary Italians and othercitizens of the world who may begin witheven the most casual interest in Romanhistory and find their work or their curiosityeasily served by quick online access anytime of day. The Archive’s digital library nowhas more than 5,000 registered users.

Because the quality of the originalscanned images was so high, the datadiscarded in a compression ratio of 20:1 didnot diminish the fine detail nor indeed anyvisual quality of the imagery, and thereduction in storage space requirements atthat ratio was an additional benefit.

For the Archive, preserving visuallylossless reproductions of these assetsmeans that even in the unthinkable eventthat the originals were lost, the invaluableinformation they contain would now beforever retrievable.

Article submitted by Alistair Maclenan ofQuary One Eleven in the U.K.

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