扇形的

What he wanted for Sydney was the effect he had noticed when tacking round the promontory at Elsinore, of the castle's piled-up turrets against the piled-up clouds and his own billowing white sails; the liberation he had felt on the great platforms of the Mayan temples in Mexico, of being lifted above the dark jungle into another world of light; the height and presence of Gothic cathedrals, whose ogival shape was to show in the cross-sections of the Sydney roof-shells; and the curved, three-dimensional rib-work of boat-building , as he had watched his own father doing it at Aalborg.

当他在艾尔西诺海岬旁作之字形航行时，天边积云朵朵，海水蓝天融为一色，海风一过，巨大的白帆随之鼓起，城堡上层叠而立的塔楼在一片湛蓝中像条游龙飘忽不定。如此景致早已收藏于心。他所向往的悉尼巨作不正是这幅美景的再现么？当他伫立于墨西哥玛雅寺庙辽阔的平台之上时，那份无拘无束的洒脱正从昏暗的丛林中抽身而出，徐徐升腾，遁入另一个光的世界。这不羁的心不正是他想施予悉尼的么？还有那直插云霄的哥特式大教堂，它们的伟岸和雍容时时撞击着他，剖开未来悉尼歌剧院的扇形穹顶吧，横截面上所展示的不正是带着尖顶拱的外形么？当他在奥尔堡傻傻地看着父亲建造船坞时，那有着优美弧线的三维肋拱结构不也是激活他未来创作的源泉么？

On the basement of conventional direct fan-beam reconstruction, this paper gives a newly improved algorithm-"fast filtering-backprojection". This method utilizes the symmetrical circle geometry to sample projection data, and reconstructs image on the Polarcoordinate firstly, then translates this reconstructed image onto the cartesian coordinate system with two interpolating operations so that the computer can show the result image on the VGA screen. This algorithm rebates the calculating backprojection greatly, and shortens a few times of reconstructing time than same kinds of means. With the size of image enlarging, the reconstructing time abates with 2 exponent times. In addition, according to the idea of parallel-beam, we rearrange the fan-beams and reconstruct image using parallel-beam method fastly. The rearranging constraint condition is given here.

本文首先在传统的扇束直接重建方法的基础上，提出了一个改进的快速滤波反投影重建算法，它利用旋转采集投影数据的圆周对称的几何关系，先在极坐标系统内进行图象的重建，然后通过两次内插运算再将图象转换到计算机显示方式下的笛卡尔坐标系中去，该方法将以往的直接重建方法中的反投影时所需的运算大大降低，并将重建时间比同类方法缩短了几倍，而且随着重建图象的尺寸的增大，重建时间以2的指数次方倍相对缩短，并获得了较好质量的重建图象；另外，又根据平行束投影重建图象的思想，对扇形射束进行了重排，然后利用平行束重建图象的方法进行扇束的重建，并推导了&扇束重排重建图象&方法的约束条件。

The split between the two groups can hardly be papered over.

这两个团体间的分歧难以掩饰。

This approach not only encourages a greater number of responses, but minimizes the likelihood of stale groupthink.

这种做法不仅鼓励了更多的反应，而且减少跟风的可能性。