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GENERATE_VIEWSHED

Updated

GENERATE_VIEWSHED

The GENERATE_VIEWSHED command allows you to perform a view shed analysis using loaded elevation grid data with a user-specified transmitter location, height, and radius. All areas within the selected radius that have a clear line of sight to the transmitter are colored with a user-specified color.

The parameters are:

  • LAYER_DESC - specifies the name to assign to the view shed layer. If no layer description is provided, the default name of "GENERATE_VIEWSHED Output" will be used.
  • XMIT_POS - indicates the transmitter location in the current projection system. This is a required parameter. This should be formatted as XMIT_POS="x_easting_longitude,y_northing_latitude"
  • FILENAME - filename of the layer(s) to process. All point features in the specified layers will be used as center points of a view shed. This parameter can be listed more than once to specify multiple input files, like FILENAME="FILENAME_1" FILENAME="FILENAME_2".The GENERATE_VIEWSHED comman must contain at least one FILENAME parameter or one XMIT_POS parameter, but not both.Note that this function can only be used in a script that runs in Global Mapper, not one that gets run via the GM_RunScript function in the SDK.
  • XMIT_HEIGHT - specifies the height above ground or sea level for the transmitter that the view shed analysis will be simulating. The value must contain the height and a units abbreviation, e.g., XMIT_HEIGHT="5 ft". This is a required parameter.
  • XMIT_HEIGHT_ABOVE_SEA_LEVEL - indicates whether the XMIT_HEIGHT value is above sea level or above ground. Use XMIT_HEIGHT_ABOVE_SEA_LEVEL=YES to specify that the transmitter height is relative to sea level. The default is "NO", i.e., the transmitter height is above ground.
  • RECEIVER_ELEV_TYPE - specifies the method used to define the receiver height. It can be one of the following values:
    • "EXPLICIT_HEIGHT" - If RECEIVER_ELEV_TYPE is not specified this is the default.
    • "XMIT_ANGLE"
    • "XMIT_ANGLE_RANGE"
  • RECEIVER_HEIGHT - required parameter that specifies the receiver height when the type is "EXPLICIT_HEIGHT". This is the minimum height above the ground or sea level from which the transmitter must be visible for the point to be considered visible. The value must contain the height and a units abbreviation, e.g., RECEIVER_HEIGHT="8 m".
  • RECEIVER_ANGLE - Optionally, you can also specify that the receiver elevation should be calculated based on an elevation angle relative to the horizon from the transmitter. This is useful if you have something like a radar dish that points up at some angle and you want to see where the signal can be seen. Specify the value in degrees, from 0 to 360. RECEIVER_ANGLE is a required parameter when the type is "XMIT_ANGLE" or "XMIT_ANGLE_RANGE".
  • RECEIVER_ANGLE_END - specifies the other end of a transmission angle range for a beam transmitted from the transmitter. Then the view shed will depict where that beam would hit the terrain surface (or some user-specified distance above the surface). RECEIVER_ANGLE_END is a required parameter when the type is "XMIT_ANGLE_RANGE". Specify the value in degrees, from 0 to 360. It must be greater than the value used for RECEIVER_ANGLE.
  • RECEIVER_HEIGHT_ANGLE - indicates the receiver height (in meters) to use when checking with restricted transmission angle. This parameter is optional, and is only used when RECEIVER_ELEV_TYPE is XMIT_HEIGHT_RANGE.
  • RECEIVER_HEIGHT_ABOVE_SEA_LEVEL - indicates whether the RECEIVER_HEIGHT or RECEIVER_HEIGHT_ANGLE value is above sea level or above ground. Use
    RECEIVER_HEIGHT_ABOVE_SEA_LEVEL=YES to specify that the receiver height is relative to sea level. The default is "NO", i.e., the receiver height is relative to the ground.
  • RADIUS - specifies how far in each direction from the transmitter to check for visibility. Typically you'd want to set this to the effective range of your transmitter. The value must contain the distance and a units abbreviation, e.g., RADIUS="25 km". This is a required parameter.
  • RADIUS_MIN - If you want to ignore areas close to the transmitter, use RADIUS_MIN to specify a minimum view radius value. The value must contain the distance and a units abbreviation, e.g., RADIUS_MIN="1 km". This is an optional parameter. The default is 0, which includes everything from the transmitter out to the selected view radius.
  • START_ANGLE - The GENERATE_VIEWSHED command allows the user to limit the view shed to a particular subsection of the complete radial area. The START_ANGLE specifies the cartographic angle, in degrees, at which the radial subregion begins. This angle is a cartographic angle, meaning that 0 degrees is north and angle increases clockwise. For example, to define a arc that starts due south, use START_ANGLE="180". This parameter is optional. The default is to perform the analysis on the full radial area.
  • SWEPT_ANGLE - specifies the number of degrees clockwise to include in the view shed. For example, if the transmitter being analyzed sweeps an arc from due south to due west, use START_ANGLE="180" SWEPT_ANGLE="90". SWEPT_ANGLE is an optional parameter. The default is 360 degrees.
  • USE_EARTH_CURVATURE - indicates whether or not to take the curvature of the earth into account while performing the view shed analysis. Use USE_EARTH_CURVATURE="YES" to specify that you want to use earth curvature. This parameter is optional; the default is "NO".
  • ATMOSPHERIC_CORRECTION - In addition, when earth curvature is being used, use ATMOSTPHERIC_CORRECTION specify an atmospheric correction value to be used. The atmospheric correction value is useful when determining the view shed for transmitting waves whose path is affected by the atmosphere. For example, when modeling microwave transmissions, ATMOSPHERIC_CORRECTION="1.333" is typically used to emulate how microwaves are refracted by the atmosphere. This is an optional parameter, with a default of 1.333.
  • CREATE_COVERAGE_AREAS - specifies whether or not view shed coverage area (polygon) features should be generated for those areas that are visible. These generated area features then behave just like any other vector feature and can be exported to vector formats, like Shapefiles, for use in other software. Use CREATE_COVERAGE_AREAS="NO" to disable this; the default is "YES".
  • SHOW_HIDDEN_AREAS - indicates whether or not the generated view shed will cover those areas that would NOT be visible, rather than those that would be visible from the transmitter location. Use SHOW_HIDDEN_AREAS="YES" to enable this functionality. The default is to show visible areas.
  • TREAT_INVALID_AS_ZERO - indicates that invalid or missing values should be treated as zero. The default is "YES". Use TREAT_INVALID_AS_ZERO="NO" to turn this off.
  • COLOR - specifies the color to use to display view shed areas. Use an RGB(red,green,blue) specification, for example, COLOR="RGB(0,255,0)" will create green areas.
  • FRESNEL_FREQ - allows you to have the view shed analysis also check that a certain portion (FRESNEL_PCT_CLEAR) of the first Fresnel zone for a transmission of a particular frequency is clear. Use FRESNEL_FREQ to specify the frequency, in GHz. For example, FRESNEL_FREQ="2.4" specifies a frequency of 2.4 GHz.
  • FRESNEL_PCT_CLEAR - specifies the percent of the first Fresnel zone that must be clear. The typical standard is that good visibility requires that at least 60% (the default) of the first Fresnel zone for the specified frequency be clear of obstructions. Specify the value as a percent, e.g., FRESNEL_PCT_CLEAR="70" will use 70%. This is an optional parameter, which will only be used if FRESNEL_FREQ is also specified.
  • FRESNEL_PCT_CLEAR_MAX - the maximum percent of 1st Fresnel zone that must be clear (default is 100.0). If you specify a maximum Fresnel zone percentage clear other than 100%, only those locations where the minimum percentage of the 1st Fresnel zone that is clear is between your specified percentages will be marked as visible. This is an optional parameter, which will only be used if FRESNEL_FREQ is also specified.
  • PATH_LOSS_FREQ - specifies the signal frequency in GHz for the free space path loss calculation. This allows you to display the power at any given location taking free space path loss into account.
  • PATH_LOSS_TOTAL_POWER - specifies the total power in dB from the rest of the link budget (i.e. transmission power plus antenna gain minus any other power losses excluding free space path loss).
  • GEN_POWER_GRID - indicates whether or not to create a grid of the remaining power at each location. Then as you move the cursor over the view shed you can see the remaining power. In addition the view shed will get more transparent as the signal power gets lower.
  • USE_VECTOR_HEIGHTS - indicates whether or not loaded vector data with elevation values should be considered when performing the view shed analysis. This allows you to use things like buildings, fence lines, towers, etc. to block portions of the view, creating a more realistic view shed. The default is to not use vector data. Use USE_VECTOR_HEIGHTS="YES" to specify that you want to use heights from vector data.
  • VECTOR_AREAS_HIDDEN - specifies that any locations within an obstruction area will be marked as hidden, rather than only those that actually would be hidden. The default is "NO".
  • VECTOR_HEIGHTS_ABOVE_SEA_LEVEL - specifies whether the elevation values stored with vector features are relative to the ground or relative to mean sea level. Typically heights for vector features are specified relative to the ground. If any area features are included and their heights are relative to the ground, the obstruction heights within those areas will be increased by the specified amount, but any receiver heights will still be based on the terrain. This makes things like wooded areas very easy to model. The default is "NO" (heights are relative to the ground). To specify that vector heights should be relative to sea level, use VECTOR_HEIGHTS_ABOVE_SEA_LEVEL="YES"
  • FIX_INVALID - indicates whether or not to automatically detect and fix invalid coverage polygons. Use FIX_INVALID="YES" to detect and fix invalid polygons. The default is "NO".
  • SPATIAL_RES - specifies spacing of grid points used to calculate the viewshed. A smaller grid spacing results in higher fidelity, but the calculation process will take longer. Typically you'll want to use the default value which is the minimum spatial resolution of all loaded data. Should be formatted as x_resolution,y_resolution. The units are the units of the current global projection. For example, if UTM was the current global projection and you wanted to use a grid with a 30 meter spacing, the parameter/value pair would look like SPATIAL_RES=30.0,30.0. You can also specify as a percentage of the default resolution by adding a percent. For example to get half the detail your double the spatial resolution value, so you would use SPATIAL_RES="200%,200%".
  • SPATIAL_RES_METERS - specifies spatial resolution to use in meters. The value in meters will automatically be converted to the current view/export projection units. For example, to do an export at 2.0 meter spacing (or as close as you can get to that in the current units), use SPATIAL_RES_METERS="2.0", or to do an export at 1.0 meters in X by 1.5 meters in Y, use SPATIAL_RES_METERS="1.0,1.5".

 

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