Visio3D: Generation of 3D perspectives based on a raster and its DEM

This application allows the user to generate a 3D perspective from a digital elevation model of any image: thematic, orthophotography or any continuous model like the DEM. There are two run modes: the Preview and Definitive modes. The preview mode is faster than the definitive mode and is recommended for determining the geometric parameters that are closest to the desired representation. In this mode it is not possible to activate the shading option. The definitive mode is slower but it produces a higher-quality three dimensional representation.

The digital elevation model (DEM) file must be in IMG format and the data type can be byte, integer, long or real. The overlapped file can be in either IMG or JPG format but it must use byte type data. The output file can also be in either IMG or JPG format but the shading option can only be used with a JPG file. The output file data is always in bytes. When the overlapped file is IMG and the output file is JPG a colour palette file is necessary for the overlapped file.

The ambit and resolution of the DEM and overlapped file do not have to be the same. This tool compares the scope of the two files and looks for the area in common. If there is a common area the process continues. If the two files have different resolutions, the file with lower resolution is resampled with a bilinear interpolation so that it has the same resolution as the other file.

In the process for generating perspective, if there is a NoData value in the DEM but a specific value in the overlapped at the same point, this value will not be displayed because, as there is no information from the DEM, it is not possible to determine the value of the overlapped file. However, if there is a NoData value in the overlapped file and a specific value in the DEM at the corresponding point, the point will be projected and displayed with the colour value corresponding to the NoData value in the colour palette (if the overlapped file is in the IMG format) or the background colour (if the overlapped file is in *. JPG format).

To generate perspective, as well as the DEM it is also necessary to introduce some parameters in relation to the viewpoint. These parameters are the azimuth and elevation angle. The azimuth can have a value between 0° and 360°, where an azimuth of 0° means that the viewpoint is located at the north of the common area. The elevation angle can be between 0° and 90°, where an elevation angle of 0° means that the viewpoint is located at the minimum height of the corresponding DEM. In addition, the vertical exaggeration must also be added. This value corresponds to the scale factor of the vertical axis and serves to highlight the topography. Therefore it helps the user to form a better idea of the shape of the terrain. When this value is 1, there is no vertical exaggeration in the final result.

The additional shading option can only be activated in the definitive mode. This process shades the values of the overlapped file depending on the topography and the position of the Sun. The Sun’s position is determined by the elevation angle (in degrees) with respect to the horizon and the azimuth with respect to the north in a clockwise direction (with 0° indicating the north). For more information on this process, see the help of the Hillshading tool.

Sintaxi:
Visio3D Option DEMFile RasterFile OutputFile ViewpointAzim ViewpointElev VerticalExaggeration (SunAzim SunElev IncremIlum MinimIlum MaximIlum ) [/OMBRA /PALETA]

Exemples:
Visio3D 1 c:\DEM.img c:\thematic.img c:\output.img 135 30 3
Visio3D 2 c:\DEM.img c:\thematic.img c:\output.jpg 45 30 3 135 30 33 5 95 /OMBRA /PALETA=c:\paleta.dbf
Visio3D 2 c:\DEM.img c:\thematic.jpg c:\output.jpg 310 30 3 225 40 33 5 95 /OMBRA
Visio3D 2 c:\DEM.img c:\thematic.img c:\output.jpg 310 30 3 /PALETA=c:\palette.dbf