GEODATA 9 second DEM and D8: Digital Elevation Model Version 3 and Flow Direction Grid 2008

The GEODATA 9 Second Digital Elevation Model (DEM-9S) Version 3 is a grid of ground level elevation points covering the whole of Australia with a grid spacing of 9 seconds in longitude and latitude (approximately 250 metres) in the GDA94 coordinate system. Version 3 of the DEM-9S was calculated by Version 5.2.2 of the ANUDEM procedure (Hutchinson 2007) from comprehensively revised and augmented national GEODATA-250K topographic source data (AUSLIG 1992, Geoscience Australia 2003, Geoscience Australia 2006) using Version 5.2.2 of the ANUDEM elevation gridding procedure. The source data included revised versions of GEODATA-250K elevation points, streamlines, cliff lines and waterbodies, trigonometric points from the National Geodetic Database and additional elevation and sink point data digitised by the Fenner School from 1:100K source material. Version 5.2.2 of the ANUDEM procedure incorporates major upgrades to the modelling of streamlines, lakes, cliff lines and the coastline. GEODATA 9 Second Flow Direction Grid (D8-9S) has been released for the first time with Version 3. The D8-9S is a corresponding grid describing the principal directions of surface drainage across the whole of Australia. This grid was calculated by the ANUDEM procedure as it derived the DEM-9S. It incorporates the data streamline structure and describes the drainage structure continent-wide. It can be used to delineate streamlines and associated catchment boundaries for the DEM-9S. This is particularly useful in low relief areas where drainage structure is not reliably defined by the DEM-9S elevations alone. The product can be used for applications requiring accurate representation of absolute elevation values. The elevation of source data high points (hills or mountains) is well represented in Version 3. The 1:250,000 source scale of the elevation grid makes the product useful for national, State-wide and regional applications. For more detailed information please refer to the User Guide below. Product Information Coverage: Australia, excluding external territories Currency: 2008 Coordinates: Geographical Datum: Horizontal: GDA94; Vertical: AHD71 Available Formats: GeoTIFF

GEODATA 9秒数字高程模型（Digital Elevation Model，DEM-9S）第3版，是覆盖澳大利亚全境的地面高程点网格，采用GDA94坐标系，经纬度网格间距为9秒（约250米）。DEM-9S第3版由ANUDEM高程网格化程序5.2.2版（Hutchinson 2007），基于经过全面修订与扩充的国家GEODATA-250K地形源数据（AUSLIG 1992、Geoscience Australia 2003、Geoscience Australia 2006）计算生成。该源数据包含修订后的GEODATA-250K高程点、流线、崖线与水体数据，国家大地数据库中的三角点，以及由芬纳学院从1:10万原始资料中数字化得到的额外高程点与汇水点数据。ANUDEM程序5.2.2版对流线、湖泊、崖线与海岸线的建模进行了重大升级。

DEM-9S第3版首次同步推出GEODATA 9秒流向网格（D8-9S）。D8-9S为配套网格，用于描述澳大利亚全境地表径流的主方向。该网格由ANUDEM程序在生成DEM-9S的过程中同步计算得到，整合了流线结构数据，完整刻画了整个大陆的径流系统，可用于勾勒DEM-9S对应的流线与相关汇水区边界。在仅依靠DEM-9S高程数据无法可靠确定径流结构的低起伏区域，该产品的优势尤为显著。

该产品可应用于需要精准表征绝对高程值的场景，第3版中源数据高点（丘陵或山地）的高程得到了良好还原。该高程网格的源数据比例尺为1:25万，适用于国家级、州级与区域级应用。如需获取更多详细信息，请参阅下述用户指南。

产品信息：
覆盖范围：澳大利亚全境（不含海外领地）
数据时效性：2008年
坐标系：大地基准——水平基准为GDA94，垂直基准为AHD71
可用格式：GeoTIFF