The application of visibility analysis of MiraMon determines, through the Digital Elevation Model (DEM), which pixels are visible and which are not, via a set of observers or viewpoints. In this version, the observers have to be specific objects in structured PNT format; they can be 3D objects, in which case the height will be known (it is possible that they be elevated from the ground, for example in a tower), or 2D, when the height will have to be determined through provided DEM. The calculation of this height and the heights of the points that determine the topographic profiles can be done by nearest neighbour, bilinear interpolation or bicubic interpolation. A complementary height, 3D or calculated, can be added to the height of the observer (equal at all the points), to elevate the observers and obtain a better visual field.

To determine if a pixel is visible from an observer point, the topographic profile of the line that joins the centre of the pixel to the observer has to be calculated. The program divides this line in segments of the same length as the pixel's side length and calculates the corresponding height of the points defined by these segments (by nearest neighbour, bilinear o bicubic interpolation). The pixel will be visible from the observer if none of the heights exceeds the visual line (straight line that joins the height of the pixel with the height of the observer, considering the additional elevation).

The resulting file of the visibility analysis is a categorical raster, with scope and length of pixel equal to the DEM, and with the following values and categories:

0
Not visible
1
Visible from some points
2
Visible from all the points
3
Viewpoints

These values and categories are registers of an associated DBF table, called te_visible located in the same directory as the resulting raster. The value 0 corresponds to the number of pixels that are not visible from any of the observers. The value 3 corresponds to the pixels where an observer has been located. The values 1 and 2 correspond to the pixels that are visible, 1 from all the observers (without specifying which) and 2 from all the observers at the same time. The categories 1 and 2 can be fused when there is no interest in differentiating them. The parameter TIPUS_VISIBLE implies maintaining this distinction.

If in a determined analysis it is thought necessary that the visibility property has the maximum distance, the parameter /MAX_DIST, that limits the visible pixels to those that are in a limited radius, can be defined. The limitation of the zone to be studied can also be done by defining a mask (raster or vectorial polygons), which will limit the pixels that have to be analyzed, and accelerate the calculations.

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