GRTSmh_base4frac: the raster data source GRTSmaster_habitats converted to base 4 fractions

The data source file is a monolayered GeoTIFF in the FLT8S datatype. In GRTSmh_base4frac, the decimal (i.e. base 10) integer values from the raster data source GRTSmaster_habitats (link) have been converted into base 4 fractions, using a precision of 13 digits behind the decimal mark (as needed to cope with the range of values). For example, the integer 16 (= 4^2) has been converted into 0.0000000000100 and 4^12 has been converted into 0.1000000000000. Long base 4 fractions seem to be handled and stored easier than long (base 4) integers. This approach follows the one of Stevens & Olsen (2004) to represent the reverse hierarchical order in a GRTS sample as base-4-fraction addresses. See R-code in the GitHub repository 'n2khab-preprocessing' at commit ecadaf5 for the creation from the GRTSmaster_habitats data source. A reading function to return the data source in a standardized way into the R environment is provided by the R-package n2khab. Beware that not all GRTS ranking numbers are present in the data source, as the original GRTS raster has been clipped with the Flemish outer borders (i.e., not excluding the Brussels Capital Region).本数据集的源文件为采用FLT8S数据类型的单波段GeoTIFF。在GRTSmh_base4frac数据集中，已将栅格数据源GRTSmaster_habitats（链接见原文）中的十进制（即基数为10）整数值转换为四进制分数，小数点后保留13位精度（以适配数值的取值范围）。例如，整数16（即4²）被转换为0.0000000000100，而4¹²则被转换为0.1000000000000。 相较于长（四进制）整数，长四进制分数更易于处理与存储。本方法借鉴了Stevens与Olsen（2004）的研究思路，将GRTS抽样中的反向层级顺序表示为四进制分数地址。 可参阅GitHub仓库"n2khab-preprocessing"中提交号为ecadaf5的R代码，以了解如何从GRTSmaster_habitats数据源生成本数据集。 R包n2khab提供了可将本数据集以标准化格式读取至R运行环境的读取函数。 请注意，本数据集并非包含所有GRTS排序编号，这是因为原始GRTS栅格已根据佛兰芒地区的外边界进行了裁切（即未排除布鲁塞尔首都大区）。