SOMEWHERE, there is a silvery-white Time Warner Center whose mass seems to dematerialize against the sky, a bronze Trump World Tower whose facade is an animated checkerboard, a Westin New York at Times Square with a cometlike beacon on its north side.

Somewhere, but not in New York City.

Instead, these buildings exist in the imagination of developers and designers and -- because of renderings -- in the public eye. As stand-ins, they are remarkably close to the completed projects. But a look at the differences between renderings and the buildings they depict, and among renderings themselves, casts light on a little-discussed facet of real estate and architectural development.

''It's one of those professions that's under the radar but in everyone's face,'' said Thomas W. Schaller of Manhattan, who as an architect was so inspired by the luminous watercolor renderings of Cyril Farey and the powerful drawings of Hugh Ferriss that he decided to become a renderer himself. ''The process isn't so much recording what isn't there yet, but helping it come to life.''

That process includes selling the project to several audiences. ''For the community planning board and the planning commission, we try to prove how well the project is integrated with its neighbors,'' said Costas Kondylis of Costas Kondylis & Partners, architects of Trump World Tower and many other residential buildings. That might mean peopling the rendering with pedestrians and ornamenting the sidewalks with mature trees.

''At the same time,'' Mr. Kondylis said, ''a developer has to make a presentation to the bank to show how important and substantial the development is going to be. It has to be a glossier rendering, showing how tall it's going to be and the views it's going to get.''

And finally, there is the prospective occupant to consider. ''I'm trying to sell a vision of something that hasn't been built,'' said Donald J. Trump. ''And that's not the easiest thing. I sell apartments for $25 million to people who have never seen the building.''

Mr. Trump has turned most often to Richard C. Baehr of Great Neck, N.Y., a renderer who works in tempera paints. ''Richard brings a building to life,'' he said.

Mr. Baehr, who has been a renderer for more than 45 years, said he is known as the Blue-Sky Guy. ''No client has ever requested a rainy-day rendering,'' he said.

Having trained and practiced as an architect, Mr. Baehr decided in the late 1950's to become a renderer, joining Robert Schwartz's firm. ''I just love to draw,'' he said, ''and most of architecture is not about drawing.'' Mr. Baehr opened his own office in 1962. His big break came four years later when he was hired to do renderings for Levitt & Sons, the builders of Levittown.

Levitt had projects around the country and even overseas. ''I'd do a two-story colonial on Long Island and they'd say, 'For the Maryland job, we want you to change the bricks to shingles and the roof and shutter color,' '' Mr. Baehr recalled.

His first rendering for Mr. Trump in 1978 of the Hyatt Regency Hotel required him to elevate the Pershing Square viaduct over 42nd Street in order to show the hotel's cantilevered bar and cocktail lounge.

In his rendering of Trump World Tower, the color and window articulation differ slightly from the actual building. That had to do with the decision, after the rendering was painted, to use a darker glass.

Though developers and architects may be tempted at times to manipulate a building's appearance materially in a rendering, they say it is not worth squandering credibility. In the insular world of real estate, they are sure to find themselves again before the same regulators and civic groups.

''I'm not interested in raising false expectations,'' said Todd H. Schliemann, a partner in Polshek Partnership Architects, designers of the Rose Center for Earth and Space at the American Museum of Natural History. ''These drawings travel forever. They go into donor packages. They go into The New York Times. They go into corporate brochures. They get resurrected in articles on renderings. You want to make sure that it has a relationship to the building that's there when the building is finished.''

Some illusions are allowed by convention, like removing foreground objects. That is illustrated by the rendering of the Westin New York hotel, designed by Arquitectonica. Such a bottom-to-top view, looking south on Eighth Avenue, does not correspond to reality because the Times Square Hotel stands stoutly in the way.

The rendering also shows a glass-enclosed base on Eighth Avenue and a lighted arc on the north facade that do not exist.

On the other hand, as the photograph of the south facade makes clear, the spirit of the rendered version -- a tower sliced along an arc, with earthy bronze tones on one side and celestial blue colors on the other -- was carried through with considerable fidelity. ''The whole design process started from a watercolor,'' said John T. Livingston, president of the Tishman Urban Development Corporation, the developer of the Westin.

Watercolor is not just a romantic or old-fashioned medium, said Mr. Schaller, a renderer who began his career as an architect in Boston, but a way ''to apply a sense of luminosity to more modernist design.''

His view of the Time Warner Center on Columbus Circle depicts buildings that seem to glow from within, as opposed to the exactly detailed digital version produced by Archimation. (Based in Berlin, Archimation is working with Studio Daniel Libeskind on plans for the World Trade Center site.)

Neither rendering depicts the Time Warner Center seen most often by passers-by, which is typically grayer or bluer and certainly darker. But at some moments, as happened recently when the skies were so roiled in the wake of Hurricane Isabel, the facade can positively shimmer in silver.

''The challenge is how to capture what we see through time,'' said Jeffrey Holmes, an associate partner in Skidmore, Owings & Merrill, architects of Time Warner Center. ''We look at a building temporally. We move around it and the sun is changing. To take a snapshot is never ideal.''

For that reason, Mr. Schaller said, a hand-crafted rendering better conveys the sense of an evolving idea than a digital image that implies a fully finished design.

''What I really, sincerely try to do is have the viewer sense what the building might feel like rather than what it looks like,'' Mr. Schaller said. ''What we do at best is tell the story of the design, capturing the spirit and not necessarily the specifics of materials that may or may not be selected.''

On the other hand, the New York Jets have found that the literalism of a digital rendering helps convey the possibility that an enormous stadium might find a place on the far West Side of Manhattan. ''Photo-realism allows people to envision what it could look like in New York City,'' said Thad Sheely, the vice president of development.

Bridging the divide between digital and hand-done renderings, Lee Dunnette of Allentown, Pa., used a computer model to help to depict the intricate, concave herringbone pattern of the Guastavino-designed vaults in the Food Emporium at Bridgemarket, under the Queensboro Bridge. The rest was done with pen and ink and airbrush.

Even as strong a digital proponent as Matthew Bannister, co-founder of Dbox on West 14th Street, sees his studio concerning itself with the same questions that faced Canaletto as he set out to portray Venice in the 18th century: perspective, time of day, composition of the frame.

''The computer, at the end of the day, is just a tool, like a brush,'' he said. ''The computer has led a lot of people to believe that they are artists. And they are not. If you let a computer cook it for you, you're using it as a recipe, but you're not a chef.''

Ingenuity and enterprise still count. Dbox was called on to render a clinical-skills room at the New York Weill Cornell Medical Center. The image had to include doctors. James Gibbs, a co-founder of the studio, asked his father, who works at the Weill Medical College of Cornell University, to send some lab coats and stethoscopes by Federal Express. Dbox staff members posed with these for photographs that were added as composites to the rendering.

A penchant for detail was evident the other day, on one monitor after another, at the Dbox office in the meatpacking district. Christian Eriksson was building a digital, three-dimensional model of a Universal Gym Equipment cable crossover machine, just one element in a larger rendering of a gym at a new apartment building by Richard Meier & Partners on Charles Street.

Nearby, Lek Jeyifous was working with Dan Southgate on an aerial view of the North Carolina Museum of Art in Raleigh, in an expansion designed by Thomas Phifer & Partners. The image was strikingly realistic. There were even wisps of stratocumulus clouds between the viewer and the verdant landscape below. Demonstrating how a digital rendering is essentially made of layers of different information, Mr. Jeyifous selected different functions on a pop-up window to show or suppress features like shadows, building elements, pathways, people and even outdoor sculptures.

A few feet away, Jon Doyle was making adjustments to the Web site that Dbox has created for the architectural firm Davis Brody Bond (www.davisbrody.com). And Gloria Kim and Gina Matsui were rendering a tower in Beijing for the San Francisco office of Skidmore, Owings & Merrill.

Dbox renderings have alerted architects to the fact that the cornices they have designed will not align with adjacent buildings and that the fiber-optic displays they have placed behind a glass curtain wall will be invisible from nearby vantages.

This kind of collaborative dialogue is embodied in the name of the firm, which refers to the pop-up dialogue boxes on computers. Dbox was founded in 1996 by Mr. Gibbs, Mr. Bannister and Charles d'Autremont.

The studio came to wide attention three years later when it rendered the fantastically complex sphere-in-a-glass-box structure of the Rose Center. The Dbox image even showed shadows cast by structural elements as they fell over the curved surface of the Hayden Planetarium.

Having modeled every nut and bolt of the building, Mr. Bannister said it was eerie to enter the actual space. ''I knew my way around, but I couldn't float around,'' he said. ''I had to walk.''