PNG是20世纪90年代中期开始开发的图像文件存储格式,其目的是企图替代GIF和TIFF文件格式,同时增加一些GIF文件格式所不具备的特性。1994年,Unysis公司宣布GIF拥有专利的压缩方法,要求开发GIF软件的软件制造商交纳一定费用,该事件成为网...PNG是20世纪90年代中期开始开发的图像文件存储格式,其目的是企图替代GIF和TIFF文件格式,同时增加一些GIF文件格式所不具备的特性。1994年,Unysis公司宣布GIF拥有专利的压缩方法,要求开发GIF软件的软件制造商交纳一定费用,该事件成为网络图像GIF和JPEG两大图像格式独霸天下的格局被打破,促使免费的PNG图像格式的诞生。PNG(Portable Network Graphic Format),中文名称为便携式网络图像格式,名称来源于非官方的“PNG's Not GIF”是一种位图文件存储格式,读成“ping”。1996年10月1日由PNG向国际网络联盟(World Wide Web Consortium)提出并得到推荐认可标准,并且大部分绘图软件支持了PNG这种格式,并最终促使微软公司从IE4.0版本开始支持PNG图像浏览。PNG用来存储灰度图像时,灰度图像的深度可多到16位,存储彩色图像时,彩色图像的深度可多到48位,可以呈现248种颜色,并且还可存储多到16位的α通道数据。PNG使用从LZ77派生的无损数据压缩算法LZ77F,LZ77F是一种词典编码算法。展开更多
We have developed a web-based processing system that can simulate positive and negative sea level changes globally by selecting the best Digital Elevation Model (DEM) for a target region from multiple DEMs. A PNG elev...We have developed a web-based processing system that can simulate positive and negative sea level changes globally by selecting the best Digital Elevation Model (DEM) for a target region from multiple DEMs. A PNG elevation tile format is used as the DEM format, which reduces the DEM data size. The PNG tile format implements client-based processing, and the DEM data are provided from different websites. In addition, the smart tile architecture is adopted, which enables on-demand simulation by adding a tile conversion process (<em>i.e.</em>, a DEM selection process) during image drawing by using JavaScript. To demonstrate the system, we have employed three DEMs,<em> i.e.</em>, the Geospatial Information Authority of Japan (GSI) map (~10-m resolution), the ASTER Global Digital Elevation Models (ASTER GDEM version 3) as global land area (~30-m resolution), and the General Bathymetric Chart of the Oceans as bathymetric data (~1000-m resolution). The ASTER Global Water Bodies Database is also used in the data selection process. The GSI provides their DEM in a PNG elevation tile format, and the other data are provided by the Geological Survey of Japan in PNG elevation tile format. We assume the current DEM sea level as 0 m, and the sea level can be changed to an arbitrary integer value (<span style="white-space:nowrap;">−</span>10,000 to 10,000 m). Combining ASTER GDEM for land and GEBCO for sea makes it possible to target DEM of the whole earth. Moreover, it was shown that if a higher resolution DEM is available, it is possible to combine the higher resolution DEM in that area. The combining the PNG elevation tile format with the smart tile architecture demonstrates the possibilities of a client-based web processing service like that of the server-based OGC Web Processing Service.展开更多
文摘PNG是20世纪90年代中期开始开发的图像文件存储格式,其目的是企图替代GIF和TIFF文件格式,同时增加一些GIF文件格式所不具备的特性。1994年,Unysis公司宣布GIF拥有专利的压缩方法,要求开发GIF软件的软件制造商交纳一定费用,该事件成为网络图像GIF和JPEG两大图像格式独霸天下的格局被打破,促使免费的PNG图像格式的诞生。PNG(Portable Network Graphic Format),中文名称为便携式网络图像格式,名称来源于非官方的“PNG's Not GIF”是一种位图文件存储格式,读成“ping”。1996年10月1日由PNG向国际网络联盟(World Wide Web Consortium)提出并得到推荐认可标准,并且大部分绘图软件支持了PNG这种格式,并最终促使微软公司从IE4.0版本开始支持PNG图像浏览。PNG用来存储灰度图像时,灰度图像的深度可多到16位,存储彩色图像时,彩色图像的深度可多到48位,可以呈现248种颜色,并且还可存储多到16位的α通道数据。PNG使用从LZ77派生的无损数据压缩算法LZ77F,LZ77F是一种词典编码算法。
文摘We have developed a web-based processing system that can simulate positive and negative sea level changes globally by selecting the best Digital Elevation Model (DEM) for a target region from multiple DEMs. A PNG elevation tile format is used as the DEM format, which reduces the DEM data size. The PNG tile format implements client-based processing, and the DEM data are provided from different websites. In addition, the smart tile architecture is adopted, which enables on-demand simulation by adding a tile conversion process (<em>i.e.</em>, a DEM selection process) during image drawing by using JavaScript. To demonstrate the system, we have employed three DEMs,<em> i.e.</em>, the Geospatial Information Authority of Japan (GSI) map (~10-m resolution), the ASTER Global Digital Elevation Models (ASTER GDEM version 3) as global land area (~30-m resolution), and the General Bathymetric Chart of the Oceans as bathymetric data (~1000-m resolution). The ASTER Global Water Bodies Database is also used in the data selection process. The GSI provides their DEM in a PNG elevation tile format, and the other data are provided by the Geological Survey of Japan in PNG elevation tile format. We assume the current DEM sea level as 0 m, and the sea level can be changed to an arbitrary integer value (<span style="white-space:nowrap;">−</span>10,000 to 10,000 m). Combining ASTER GDEM for land and GEBCO for sea makes it possible to target DEM of the whole earth. Moreover, it was shown that if a higher resolution DEM is available, it is possible to combine the higher resolution DEM in that area. The combining the PNG elevation tile format with the smart tile architecture demonstrates the possibilities of a client-based web processing service like that of the server-based OGC Web Processing Service.
