Data Buffers

Terrain-3D uses data buffers for overlaying color coded grid based data on the 3D map. Several types of data buffer can be calculated. Use the “Calculate Data Buffer” button on the “Buffer” page of the 3D Options Window to calculate a new data buffer.

When a data buffer is calculated, the number and size of the cells in the buffer is determined by the current 3D area displayed in the 3D map window. The buffer data is calculated for the entire region shown in the window, and the number of cells is determined by the “Grid Size” setting on the “Data” page of the 3D Options Window (the number of cells will be the square of the Grid Size).

Terrain-3D currently supports the following data buffer types:

Signal Buffers – These are buffers that contain field strength values calculated by a propagation model (Terrain 3D currently supports the Longley/Rice (ITM) and modified PTP propagation models).

Shadow Depth Buffers – These buffers contain the amount of clearance that the line of sight has with the terrain along a path to each point in the buffer.

Population Density Buffers – A representation of population density based on census data.

Population Count Buffers – These buffers contain a simple count of all of the people located within each cell of the buffer.

Calculating Signal Buffers

When calculating a signal buffer the transmitter properties window will be displayed, where you can enter the transmitter properties or load a transmitter out of the FCC database. You will also need to select a propagation model and set the propagation properties (see Propagation Models for more information).

After you have entered the parameters signal calculation will begin. A progress window will appear showing the calculation progress. When the signal calculations have completed, a window will appear asking if you wish to apply the current color buffer. If you choose not to display it at that time you can display it by clicking the “Apply the current color buffer” button on the “Buffer” page of the 3D Options Window.

Calculating Shadow Depth Buffers

A shadow buffer contains the amount of clearance that the line of sight has with the terrain profile between the transmitter and the point in question. If this value is positive, then there is unobstructed “line of sight” between the transmitter and receiver (the magnitude indicates the smallest amount of clearance). If it is negative, then the “line of sight” is obstructed by the terrain and the magnitude indicates the maximum amount of obstruction along the path.

To calculate a shadow buffer, the transmitter latitude, longitude, and height as well as the receiver height, profile spacing, and earth’s curvature K constant must be specified. The profile spacing is the amount of space (in km) between terrain samples that is used in profile generation. A profile spacing of 0.1 km is consistent with the maximum resolution of the 3 second terrain database. To use flat earth (no earth’s curvature), specify a K constant of 0.

After pressing “OK “ the shadow buffer will be calculated and a progress window will be displayed. When the calculations are complete, the color buffer will automatically be applied.

Calculating Population Count and Density Buffers

Population buffers are quickly calculated and then automatically applied to the current 3D map. Population counts are calculated by summing the population of each census block contained within each cell. A population density buffer is the number of people in each cell divided by the area of the cell (in square kilometers). Because the size of the cells in the buffer are determined by the area being viewed, the population counts and densities will change depending on the area and resolution at which they are calculated.