Analyze a triangle or rectangle grade does not give an overall idea, i.e., parameters being modeled, so it is convenient to transform the grid in a more suitable product to be analyzed
TerraLib allows generate gray level image from the DTM considering the
interval between 0 (black) and 255 (white), i.e., grade real numbers
are transformed in integer values, in gray level range, or in a
shadowed image which consider the azimuth angle and the light source
elevation.
Gray-level image generation to a terrain numeric model, where pixels
will contain gray level, consist of distributing quota minimum and
maximum values obtained from rectangle grade in gray levels from 0 to
255 using a linear equation (y = ax +b).
The output image resolution (in meters) will have the same rectangle
grade that generated it. To generate an image with a different XY
resolution, it is necessary to generate another grade with the wanted
resolution, and then generate the gray level image. This happens
because each grade cell will correspond exactly to a pixel in output
image where minimum quota values will be represented by dark pixels and
the maximum values by clear pixels.
A shadowed image generated from a terrain numeric model will make
possible to view terrain differences in each region. It is generated
from the rectangle grade on which is applied a light model. This light
model determines the reflected light intensity in a surface point
considering a certain light source The model depends on the light
source that can be day light or other light source, and the surface
reflexion.