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在地理坐标系下怎样生成山影(hillshade)和坡度(slope)
作者:独木舟 日期:2009-11-24
很久前看到的一篇文章了，现在翻译成中文与大家分享一下
在地理坐标系下怎样生成山影(hillshade)和坡度(slope)
摘要
当用ArcGIS处理山影或坡度的时候，高程单位(Z units)必须与水平面(x,y)单位一样。这样在处理地理坐标下的数据的时候就出现问题，原因是水平距离单位为经纬度。
在一些情况下，当高程单位是米时，0.00003是一个被推荐的符合实际的Z因子(Z factor)值。虽然这个值还在使用，这篇文章给出了一个更精确的方法来确定当高程单位是米时的Z因子。
过程
下面过程假定生成山影和坡度的时候高程的单位为米。如果高程单位为英尺(feet)，首先使用栅格计算器把栅格乘以0.3048这个转换因子，这样高程单位就是米了。
1.确定目标区域中间的纬度
2.转换度单位为弧度单位
1度=0.0174532925弧度
3.用弧度值按下面等式计算
Z因子(Z factor) = 1.0 / (113200 * cos(<弧度制的纬度>))
4.在山影和坡度工具中使用这个计算的Z因子
后记
根据上文提到的Z因子一般取值0.00003算出的坡度与投影UTM后算的坡度偏差挺大，不知道文章中为什么说是推荐值。而根据本文方法算的Z因子算出的坡度与投影UTM后算的坡度较吻合，因此此法准确度较高。
原文：
HowTo: Create a hillshade or slope using data in Geographic coordinates
Article ID:29366
Software: ArcGIS - ArcEditor 8.1, 8.1.2, 8.2, 8.3, 9.0, 9.1, 9.2, 9.3 ArcGIS - ArcInfo 8.0.1, 8.0.2, 8.1, 8.1.2, 8.2, 8.3, 9.0, 9.1, 9.2, 9.3 ArcGIS - ArcView 8.1, 8.1.2, 8.2, 8.3, 9.0, 9.1, 9.2, 9.3 ArcView GIS 3.0, 3.0a, 3.0b, 3.1, 3.2, 3.2a, 3.3
Platforms:N/A
Summary
When performing a hillshade or slope function in ArcGIS, the Z units are presumed to be the same as the horizontal (x,y) units. When working with data in geographic coordinates, this is a problem because the linear distance of a degree of latitude varies.
In some cases, a value of 0.00003 was suggested as the Z factor to account for the actual Z unit in meters. While that value can still be used, this article presents a more accurate method of determining the Z factor when the Z units are in meters.
Procedure
The following procedure assumes the Z units of the raster being used to generate the hillshade or slope are meters. If the Z units of the data being used is feet, first use the raster calculator to multiply the raster by the conversion factor 0.3048, so that the z units are meters.
1.Determine what the middle latitude of the area of interest is.
2.Convert that degree value to radians.
1 degree = 0.0174532925 radians
3.Use the value in radians in the following equation:
Z factor = 1.0 / (113200 * cos(<input latitude in radians>))
4.Use this calculated Z factor in the hillshade or slope tool.
Created: 6/3/2005
Last Modified: 8/26/2008
在地理坐标系下怎样生成山影(hillshade)和坡度(slope)
摘要
当用ArcGIS处理山影或坡度的时候，高程单位(Z units)必须与水平面(x,y)单位一样。这样在处理地理坐标下的数据的时候就出现问题，原因是水平距离单位为经纬度。
在一些情况下，当高程单位是米时，0.00003是一个被推荐的符合实际的Z因子(Z factor)值。虽然这个值还在使用，这篇文章给出了一个更精确的方法来确定当高程单位是米时的Z因子。
过程
下面过程假定生成山影和坡度的时候高程的单位为米。如果高程单位为英尺(feet)，首先使用栅格计算器把栅格乘以0.3048这个转换因子，这样高程单位就是米了。
1.确定目标区域中间的纬度
2.转换度单位为弧度单位
1度=0.0174532925弧度
3.用弧度值按下面等式计算
Z因子(Z factor) = 1.0 / (113200 * cos(<弧度制的纬度>))
4.在山影和坡度工具中使用这个计算的Z因子
后记
根据上文提到的Z因子一般取值0.00003算出的坡度与投影UTM后算的坡度偏差挺大，不知道文章中为什么说是推荐值。而根据本文方法算的Z因子算出的坡度与投影UTM后算的坡度较吻合，因此此法准确度较高。
原文：
HowTo: Create a hillshade or slope using data in Geographic coordinatesArticle ID:29366
Software: ArcGIS - ArcEditor 8.1, 8.1.2, 8.2, 8.3, 9.0, 9.1, 9.2, 9.3 ArcGIS - ArcInfo 8.0.1, 8.0.2, 8.1, 8.1.2, 8.2, 8.3, 9.0, 9.1, 9.2, 9.3 ArcGIS - ArcView 8.1, 8.1.2, 8.2, 8.3, 9.0, 9.1, 9.2, 9.3 ArcView GIS 3.0, 3.0a, 3.0b, 3.1, 3.2, 3.2a, 3.3
Platforms:N/A
Summary
When performing a hillshade or slope function in ArcGIS, the Z units are presumed to be the same as the horizontal (x,y) units. When working with data in geographic coordinates, this is a problem because the linear distance of a degree of latitude varies.
In some cases, a value of 0.00003 was suggested as the Z factor to account for the actual Z unit in meters. While that value can still be used, this article presents a more accurate method of determining the Z factor when the Z units are in meters.
Procedure
The following procedure assumes the Z units of the raster being used to generate the hillshade or slope are meters. If the Z units of the data being used is feet, first use the raster calculator to multiply the raster by the conversion factor 0.3048, so that the z units are meters.
1.Determine what the middle latitude of the area of interest is.
2.Convert that degree value to radians.
1 degree = 0.0174532925 radians
3.Use the value in radians in the following equation:
Z factor = 1.0 / (113200 * cos(<input latitude in radians>))
4.Use this calculated Z factor in the hillshade or slope tool.
Created: 6/3/2005
Last Modified: 8/26/2008
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