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当不编制森林分布图时,可用透明网点板在象片上布置样地,进行森林类型判读,按成数抽样方法推算各类型面积。由于判读误差、航摄后地类的变更、以及地形起伏等因素所致,各类面积成数估计可能产生偏差,为此应抽取部分象片样地进行实地检验改正。一般工作步骤如下:
When the forest distribution map is not prepared, the transparent halftone plate can be used to arrange the plots on the image for interpretation of the forest type and to calculate the area of each type according to the sampling method of the number of pieces. Due to the discrepancy of interpretation, the alteration of aerial images after aerial photographing, and the undulation of topography, the estimation of various types of area percentages may be biased. Therefore, part of the sample areas should be taken for field inspection and correction. General work steps are as follows: