Analyzing the image of SEM of clay soil is a very important method to study the soil microstructure. But most of the traditional method is just qualitative. In fact

there are much information in the image of SEM

for example

the distance from the grain surface to the photographic plate. The authors apply GIS to recreate the three-dimension model of the clay through the SEM image. Also

the method of computing the porosity by GIS technique is introduced

including the two-dimension method and three-dimension method. At last

the analysis and comparison of these two methods are carried out. The result shows that the porosity obtained from two-dimension image (binary image) is affected by the threshold in binarization process

the lower the threshold

the more the volume of the grains

and the lower the porosity. Because the porosity obtained from three-dimension image is gotten directly from the grey-scale image and is not affected by the binarization process

it is more reasonable.