# 代写assignment-三角棱镜法的计算

The triangular prism method is a single and a unique method which was put forward by Clarke (1986) who used to same for the purpose of calculation of the topographic surface. In the present times, this method has been largely applicable to a number of remote sensing images. With the help of the same, one can easily do the calculation for the raster representation of any of the earth’s surface. In this method the raster representation of the earth surface has been used as a DEM. The images will be observed in the form of grid represented by ‘x’ and ‘y’ coordinates and the value of the pixel is assumed to be ‘z’ value. This value helps in providing a vertical dimension to the cell. While taking out the values for the pixels which constitute the four corners of the square the calculation for the mean value will be done (Morris et al 975). A vertical line is then which is found to be equivalent to the mean value has to be calculated by drawing the same from the center of the square grid. In addition to this the straight lines have been drawn which may be joining towards the top side of each and every corner lines and also with the center lines. This gives the definition of the four triangular surfaces which may also comprise of a triangular prism. With the help of the trigonometric formulae, one can easily calculate the area of the top side of the prism (Dingler et al112).

There is a continuous repetition of this process for every step size. Each of the computation which may follow each other takes the area of the cell which may be exponentially larger than the previous one. This kind of process will be continued until there is the calculation of the area of the entire image in a single cell. With each of the succeeding computation, the cell area is calculated, which is larger than the previous one. The process is continued until the whole image area has been calculated in the single cell. However, after doing this image resolution, there is a loss of information when the individual pixels are been replaced by the mean observed at the center (Hudson & Blake 73). After this the logs of the total surface area will be obtained. After this, the calculation of the fractal dimension will be done with the help of taking the slope of regression line and substituting the same in the equation of the slope. It will be observed that there is a decrease in the total surface area with the increase in the value of the step size, the slope of the regression line will be negative.

Fractal analysis estimates fractal dimensions. The three fractal surface measurements methods implemented in ICAMS, including the isarithm, variogram, and triangular prism methods. The isarithm method will be applied, because the yields accurate and reliable results for all surfaces, whereas the variogram method is only accurate for surfaces of low dimensions such as topographic surfaces (Lam 1997).
Spatial autocorrelation method helps understand the degree to which one object is similar to other nearby objects.