SMS:Z Magnification: Difference between revisions

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In most situations simulated in SMS, the data range in the horizontal direction is not similar to the data range in the vertical direction.  For example, when simulating a river reach, the river may cover miles (or kilometers) along the length of the river, but in the z-direction, the change in elevation will only be in the tens to hundreds of feet (meters).  In an opposite situation, when working with a coastal circulation model in geographic coordinates, the horizontal variation of the data may only be a few degrees, while the vertical change in depth can be thousands of meters.  
In most situations simulated in SMS, the data range in the horizontal direction is not similar to the data range in the vertical direction.  For example, when simulating a river reach, the river may cover miles (or kilometers) along the length of the river, but in the z-direction, the change in elevation will only be in the tens to hundreds of feet (meters).  In an opposite situation, when working with a coastal circulation model in geographic coordinates, the horizontal variation of the data may only be a few degrees, while the vertical change in depth can be thousands of meters.  
When displaying data in plan view, this inconsistency of data ranges does not cause a problem.  However, when attempting to view data in an oblique view (from an angle in three dimensions), the first case of a long river ends up looking like a flat plane while the second case is just a mass of vertical bumps.  
When displaying data in plan view, this inconsistency of data ranges does not cause a problem.  However, when attempting to view data in an oblique view (from an angle in three dimensions), the first case of a long river ends up looking like a flat plane while the second case is just a mass of vertical bumps.  
To allow for intuitive display of the data in three dimensions SMS allows the specification of a Z magnification term.  This scale factor  exaggerates or reduces the relief of the data in the simulation.
To allow for intuitive display of the data in three dimensions SMS allows the specification of a Z magnification term.  This scale factor  exaggerates or reduces the relief of the data in the simulation.



Revision as of 14:57, 26 March 2013

Justification for Z magnification

In most situations simulated in SMS, the data range in the horizontal direction is not similar to the data range in the vertical direction. For example, when simulating a river reach, the river may cover miles (or kilometers) along the length of the river, but in the z-direction, the change in elevation will only be in the tens to hundreds of feet (meters). In an opposite situation, when working with a coastal circulation model in geographic coordinates, the horizontal variation of the data may only be a few degrees, while the vertical change in depth can be thousands of meters. When displaying data in plan view, this inconsistency of data ranges does not cause a problem. However, when attempting to view data in an oblique view (from an angle in three dimensions), the first case of a long river ends up looking like a flat plane while the second case is just a mass of vertical bumps.

To allow for intuitive display of the data in three dimensions SMS allows the specification of a Z magnification term. This scale factor exaggerates or reduces the relief of the data in the simulation.

Auto Z magnification

SMS also includes the option to compute a Z magnification term automatically. This option is turned on by default. This means that every time SMS frames the data in a display, the Z magnification term is computed to ensure that the scaled span of the vertical data is just under 10% of the horizontal data. This prevents the data from becoming too flat (unless it is totally flat) and prevents the relief from becoming to drastic or dramatic.

Since the Z magnification value is computed when SMS frames the data, modifications to the data that change the Z range are not incorporated into the magnification value until a frame command is encountered. This may result in difficulties rotating a scene in three dimensions. Operations like generating new elevation data for a mesh by interpolation from a raster or scatter set may cause this to occur.

The user can disable the auto Z magnification feature by unchecking the toggle next to the Auto z-mag. When the toggle is unchecked, an edit field appears allowing the user to specify a Z magnification value. The value is set to the previously computed auto Z magnification.