NCL_GETools API

September 10, 2013

Updated May 22, 2014

Introduction

 

NCL_GETools is a library for generating KML output with NCL.  It was developed by Mohammad Abouali during the summer 2013 SIParCS internship program. The library is being made available on a preliminary basis to gauge user interest and to gather further use-cases and requirements. Given sufficient interest, the library may be further developed and become a standard component of NCL. Note that NCL_GETools requires NCL v6.2.0 or later.

 

The library consists of a set of 7 high-level procedures. Each procedure accepts a resources argument, as per common NCL idiom; this argument is typically a boolean variable, assigned the value True, onto which one or more resource-attributes are attached. A rich set of new resources have been introduced with NCL_GETools to control various aspects of the graphical appearance and behavior of the KML output when rendered within Google Earth. Each resource has a suitable default setting.

 

It should be noted in passing that an alternative KML library for NCL has been developed by Ryan Pavlick. That API operates at a level closer to the underlying KML structure, and as such, is both inherently more powerful but likely requires more knowledge about KML. See https://github.com/rpavlick for Ryan’s KML-library and a collection of other tools he has developed for NCL.

 

Users access the procedures that comprise NCL_GETools by including the following line in their scripts:

 

  load "$NCARG_ROOT/lib/ncarg/nclscripts/contrib/NCL_GETools.ncl"

 

The procedures and the resources they accept are described next. Familiarity with Google Earth is presumed.

 

Point2KML

 

Generates a georeferenced marker, along with optional annotations, as seen in Figure 1.  The geolocation may be specified either by longitude-latitude values, or via postal address.

 

Text Box:  Figure 1.

Prototype

procedure Point2KML(

    filename : string

    opt : logical

)

Arguments

filename

A name for the resultant KML output file.

opt

Optional resources.

Resources recognized

Visibility : boolean

 Determines whether the marker is initially visible when the KML is loaded into Google Earth.

Description : string

Free-form text that appears in the annotation panel associated with the marker (see Fig. 1).

Lon : float

Lat : float

Specifies the longitude and latitude values respectively of the marker's location.

Address : string

Specifies the location of the marker via postal address. Note if both Address and Lon/Lat are given, Address will be ignored.

StoragePath : string

A pathname prefix for the KML output file. The default is the current directory.

Verbose : boolean

When set to True, Point2KML writes diagnostic output to stdout. Default is False.

 

Examples

The two markers shown in Fig. 1 were generated by the following scripts.  Location specified by address:

 

load "$NCARG_ROOT/lib/ncarg/nclscripts/contrib/NCL_GETools.ncl"

begin

            ; This example shows how to create a point based on known address

            Opt=True

            Opt@Name="Table Mesa Lab - Road"

            Opt@Address="1850 Table Mesa Drive, Boulder, CO"

            Opt@Description="The road to National Center for Atmospheric Research (NCAR) - http://ncar.ucar.edu"

            Opt@Verbose=True

             

            kml_FileName="NCAR_ML"

            Point2KML(kml_FileName, Opt)

end

 

Location specified by longitude-latitude:

 

load "$NCARG_ROOT/lib/ncarg/nclscripts/contrib/NCL_GETools.ncl"

begin

            ; This example shows how to create a point based on known lat/lon Coordinate

            Opt=True

            Opt@Name="Table Mesa Lab - Building"

            Opt@Lat=39.9779329120415

            Opt@Lon=-105.2749947520585

            Opt@Description="National Center for Atmospheric Research (NCAR) - http://ncar.ucar.edu"

            Opt@Verbose=True

             

            kml_FileName="NCAR_MLB"

            Point2KML(kml_FileName, Opt)

end

 

SHP2KML

 

Generates extruded polygons from a Shapefile. Figure 2 depicts population data for Colorado counties by height and coloring of the polygons.

Text Box:  Figure 2.

Prototype

procedure SHP2KML(

    shapefileName : string

    kmlOutputFile : string

    opt : logical

)

Arguments

shapefileName

filename of the shapefile to be read.

kmlOutputName

filename for the KML output file.

opt

optional resources.

Resources recognized

VarName : string

Name of the variable within the shapefile that should be used to determine height and/or coloring of the polygons. Must be specified.

MinData : numeric

MaxData : numeric

These resources can be used to clamp the range of values for variable VarName.

NoData : numeric

Value to indicate missing data in VarName.

MakeLogScale : boolean

Apply a log-scale in mapping VarName values to colors/height. Default is False.

Extrude : boolean

Determines whether polygons should be extruded along the vertical axis. The default is True.

MinH : float

MaxH : float

Minimum and maximum height of the extruded polygons, in meters.

AltMode : enum

Altitude-Mode - determines how extruded polygons are positioned in space. Valid values are: absolute,  clampToGround, clampToSeaFloor, relativeToGround, relativeToSeaFloor. Default is absolute.

ConstHeight : float

Extrude polygons to a constant height (meters). Default is 3000m.

Colormap : string

Name of the colormap to be used for coloring polygons. Default is the “WhiteBlueGreenYellowRed” colormap.

ReverseColorMap : Boolean

Map colors to VarName values in reverse order.  Default is False.

UseConstOpacity : Boolean

Whether to color polygons with a fixed opacity. Default is False

ConstOpacity : float

Opacity for coloring the polygons, in the range 0 (transparent) to 100 (opaque). Default is 50.

LineWidth : float

Width of the borderlines of the polygons.

Name : string

A descriptive label generated into the KML.

Tesselate : boolean

???

StoragePath : string

A pathname prefix for the KML output file. The default is the current directory.

Verbose : boolean

When set to True, writes diagnostic output to stdout. Default is False.

Examples

load "$NCARG_ROOT/lib/ncarg/nclscripts/contrib/NCL_GETools.ncl"

begin

            SHPFileName="../ExampleData/ColoradoCounty/ColoradoCounty.shp"

            kml_FileName="ColoradoCounty"

 

            Opt=True

            ; The variable name inside the Shapefile that stores the population

            ; The height of the polygons and the color is calculated based on

            ; this variable.

            Opt@VarName="POP_2008"

            Opt@Name="County Populations"

            Opt@Verbose=True

            Opt@MakeLogScale=True

            Opt@MinH=50000         ; the minimum height [m]

            Opt@MaxH=300000       ; the maximum height [m]

 

            SHP2KML(SHPFileName,kml_FileName,Opt)

end

 

RasterTimeSeries2KML

 

Generates color plots from a time series, which may then be animated within Google Earth (Figure 3).

 

Text Box:  Figure 3.

Prototype

procedure RasterTimeSeries2KML(

    filename : string

    rasterData[*][*][*] : numeric

    xCoords[*][*] : numeric

    yCoords[*][*] : numeric

    timeTag[*] : string

    opt : boolean

)

Arguments

filename

Filename for the KML output file.

rasterData

The variable to be mapped. The shape is assumed to be [time][row][col].

xCoords

Longitudinal values for the raster grid; [row][column].

yCoords

Latitudinal values for the raster grid [row][column].

timeTag

String representation of the time coordinate values [time].

Opt

Optional resources.

Resources recognized

North : numeric

South : numeric

East : numeric

West : numeric

May be used to clip out a spatial subset of the input data.

MinData : numeric

MaxData : numeric

These resources can be used to clamp the range of values in the grid.

Altitude : numeric

Altitude (meters) at which to position the color plot.

Extrude : boolean

Determines whether the raster should be extruded along the vertical axis. The default is True.

AltMode : enum

Altitude-Mode - determines how the extruded raster is positioned in space. Valid values are: absolute,  clampToGround, clampToSeaFloor, relativeToGround, relativeToSeaFloor. Default is absolute.

PixelRatio : float

???

Colormap : string

Name of the colormap to be used for coloring polygons. Default is the “WhiteBlueGreenYellowRed” colormap.

ReverseColorMap : Boolean

Map colors to VarName values in reverse order.  Default is False.

ConstOpacity : float

Opacity for coloring the polygons, in the range 0 (transparent) to 100 (opaque). Ignored by default.

MinDataOpacity, MaxDataOpacity : numeric

Can be used to apply a linear ramp of varying opacity across the range of grid values. Specified in the range 0 (transparent) to 100 (opaque).

GridVisibility : boolean

Display the raster gridlines. Default is False.

GridAltitude : numeric

Altitude at which to display gridlines, in meters. Default is Altitude+3000.

LineWidth : float

Width for gridlines.  Default is “1”  (in units of pixels?)

LineRedColor,

LineGreenColor,

LineBlueColor : numeric

Red, green blue components that make up the color of the gridlines. Specified in the range of 0 to 255. Default triplet is 255,0,255.

LineOpacity : numeric

Opacity of the gridlines, in the range 0 (transparent) to 100 (opaque).  Default is 100.

Name : string

A descriptive label generated into the KML.

Tesselate : boolean

???

Overwrite: boolean

???  Default is False.

ForceOverWrite: Boolean

???  Default is False.

NameList: string[*]

???

CoordSystem

???

CoordUnits

???  Default is “degrees”

InterpMethod

???  Default is “bilinear”

InterpWeightFile : string

???  Default is Filename + “_wgt.nc”

KeepInterpWeightFile : Boolean

???  Default is True

SrcRegional : boolean

???  Default is True.

DstRegional : boolean

???  Default is True.

Rotation : numeric

???  Default is 0.

DataSetTitle : string

???  Default is “--”

StoragePath : string

A pathname prefix for the KML output file and PNGs. The default is the current directory.

Verbose : boolean

When set to True, writes diagnostic output to stdout. Default is False.

Example

load "$NCARG_ROOT/lib/ncarg/nclscripts/contrib/NCL_GETools.ncl"

begin

            fid=addfile("../ExampleData/ds601.0_RCPP/olr_RCPP_2002_12.nc","r")

            nFrames=20;

            olr=fid->OLR(0:nFrames,:,:)

            lat=fid->XLAT

            lon=fid->XLONG

            TimeTag=tostring(fid->Times(0:nFrames,:))

 

 

            Opt=True

            Opt@Verbose=True

            Opt@ColorMap="WhiteBlue"

            Opt@DataSetTitle="Outgoing Longwave Radiation"

            Opt@MinData=100.0

            Opt@MaxData=250.0

            Opt@MinDataOpacity=100

            Opt@MaxDataOpacity=0

            Opt@IncludeGrid=True

             

            ; The following command will create a KML file, called olr12.kml,

            ; in the current directory, since the first argument, i.e.

            ; the PATH, is set to "."

            RasterTimeSeries2KML("olr_200212_21F_VarAlpha",olr,lon,lat,TimeTag,Opt)

end

 

Velocity2KML

Generates a vector plot of time-series data (Figure 4).

Text Box:  Figure 4.

Protoype

procedure Velocity2KML(

    filename[1] : string

    u[*][*][*] : float

    v[*][*][*] : float

    lat[*][*] : float

    lon[*][*] : float

    timeTag[*] : string

    opt : logical

)

Arguments

filename

Filename for the KML output file.

u, v

U/V vector components, shaped as [time][row][col]

lat, lon

Coordinates of vector components, shaped as [row][col].

timeTag

String representation of the time coordinate values [time].

opt

Optional resources.

Resources recognized

IStride, JStride: int

Strides across U/V components. Default is 1.

Extrude : boolean

Determines whether the raster should be extruded along the vertical axis. The default is True.

Height : numeric

Altitude at which to plot vectors. Default is 3000 meters.

AltMode : enum

Altitude-Mode - determines how the extruded raster is positioned in space. Valid values are: absolute,  clampToGround, clampToSeaFloor, relativeToGround, relativeToSeaFloor. Default is absolute.

UseConstColor : boolean

Use a constant color to shade vector glyphs, as specified via Line[Red/Green/Blue]Color resources. Default is False.

LineRedColor,

LineGreenColor:

LineBlueColor : numeric

Red, green, blue components for vectors shaded a constant color, specified as values between 0 and 255. Default is 255,0,255 (i.e., magenta).

LineOpacity : float

Opacity of the vectors, in the range 0 (transparent) to 100 (opaque).  Default is 100.

LineWidth : numeric

Width of the vector glyphs (in pixels?). Default is 1.

ColorMap : string

Specifies a colormap used to color vectors by magnitude. Default is "WhiteBlueGreenYellowRed".

Name : string

Title given to the plot.

ArrowScale

???

Tesselate

???

StoragePath : string

A pathname prefix for the KML output file and PNGs. The default is the current directory.

Verbose : boolean

When set to True, writes diagnostic output to stdout. Default is False.

Example

load "$NCARG_ROOT/lib/ncarg/nclscripts/contrib/NCL_GETools.ncl"

begin

            fidu=addfile("../ExampleData/ds601.0_RCPP/u10_RCPP_2002_12.nc","r")

            fidv=addfile("../ExampleData/ds601.0_RCPP/v10_RCPP_2002_12.nc","r")

             

            nFrames=4

            u=fidu->U10(0:nFrames,:,:)

            v=fidv->V10(0:nFrames,:,:)

            lat=fidv->XLAT

            lon=fidv->XLONG

            TimeTag=tostring(fidv->Times(0:nFrames,:))

             

            Opt=True

            Opt@Verbose=True

            Opt@IStride=5;

            Opt@JStride=5;

            Opt@ArrowScale=20000.0

            Opt@Name="RCPP 2002 12 Velocity"

            Opt@LineWidth=3;

            Opt@Height=20000

            Velocity2KML("velocity_200212_HR_5F", u, v, lat, lon, TimeTag, Opt)

end

 

Path2KML

Draws a georeferenced trajectory, such as the flight path of an aircraft (the yellow line in Figure 5.)

 

Text Box:  Figure 5.

Prototype

procedure Path2KML(

    filename : string

    lat[*] : numeric

    lon[*] : numeric

    height[*] : numeric

    timeTag[*] : string,

    opt : logical

)

Arguments

filename

Filename for the KML output file.

lat, lon, height

X/Y/Z coordinates of the trajectory waypoints.

timeTag

String representation of the time coordinate values [time].

opt

Optional resources.

Recognized resources

PathName : string

Name embedded into KML file.

LineWidth : numeric

Width of the line depicting the trajectory (in pixels?). Default is 1.

LineRedColor,

LineGreenColor,

LineBlueColor : numeric

The red/green/blue components of the trajectory line color, given in values from 0 to 255. Default is 255,255,0 (i.e., yellow).

LineOpacity : float

Opacity of the trajectory line, in the range 0 (transparent) to 100 (opaque).

IconName : string

Icon used to mark waypoints along the trajectory. The name comes from a long list of possibilities supported by Google Earth (a large list has been compiled into the get_KML_IconRef() function, within the NCL_GETools.ncl source code). Default is “ylw-pushpin”.

PointRedColor,

PointGreenColor,

PointBlueColor : numeric

Color components of the waypoint markers, specified in values from 0 to 255. Default is 255,255,255 (white).

PointOpacity : float

Opacity of the waypoint markers, in the range 0 (transparent) to 100 (opaque).

AdjustHeader : logical

If true, the icon is rotated to point in the direction along the trajectory. Default is False.

Extrude : boolean

Determines whether the trajectory should be extruded along the vertical axis. The default is False.

AltMode : enum

Altitude-Mode - determines how the extruded raster is positioned in space. Valid values are: absolute,  clampToGround, clampToSeaFloor, relativeToGround, relativeToSeaFloor. Default is relativeToGround.

Tesselate : logical

??? Default is True.

StoragePath : string

A pathname prefix for the KML output file and PNGs. The default is the current directory.

Verbose : boolean

When set to True, writes diagnostic output to stdout. Default is False.

Example

load "$NCARG_ROOT/lib/ncarg/nclscripts/contrib/NCL_GETools.ncl"

begin

            ;

            ; LOADING DATA

            ;

            Data=read_ict("../ExampleData/Aircraft/mrg60_dc8_20080618_R13.ict")

 

            lat=Data(:,5);

            lon=where(Data(:,6).gt.180,Data(:,6)-360,Data(:,6))

            z=Data(:,15)*1000.0 ; converting to meter.

 

            ;

            ; Getting Time String in the format of yyyy-mm-dd_hh:mm:ss

            ;

            YYYY=tointeger(str_get_field(Data@Header(6),1," "))

            Date=jul2greg(Data(:,1)+tointeger(greg2jul(YYYY,1,1,1)))

 

            hh=tointeger(Data(:,0)/3600.0)

            mm=tointeger((Data(:,0)-hh*3600.0)/60)

            ss=tointeger(Data(:,0)-hh*3600.0-mm*60)

 

            TimeTagStr= sprinti("%0.4i",Date(:,0))+"-" \

                                   +sprinti("%0.2i",Date(:,1))+"-" \

                                   +sprinti("%0.2i",Date(:,2))+"_" \

                                   +sprinti("%0.2i",hh)+":" \

                                   +sprinti("%0.2i",mm)+":" \

                                   +sprinti("%0.2i",ss);

 

            ;

            ; Exporting the Path to KML                               

            ;

            Opt=True

            Opt@Verbose=True

            Opt@PathName="DC8 2008/06/18"

            Opt@IconName="airports"

            Opt@LineWidth=5.0

            Opt@AdjustHeading=True

            Path2KML("Aircraft", lat,lon,z,TimeTagStr,Opt)

end

Measurements2KML

Plots colored and shaped polygons to reflect a scalar quantity. Originally was conceived as a means to plot measurements from air-borne instrumentation. The triangle shape and color in Figure 5 depicts nitric-oxide values as measured by the aircraft at that instant during its flight.

Prototype

procedure Measurements2KML(

    filename : string

    lat[*] : numeric

    lon[*] : numeric,

    height[*] : numeric

    inData[*] : numeric

    timeTag[*] : string

    opt : logical

)

Arguments

filename

Filename for the KML output file.

lat, lon, height

X/Y/Z coordinates of the trajectory waypoints.

inData

The measured data.

timeTag

String representation of the time coordinate values [time].

Opt

Optional resources.

Recognized Resources

NsidePolygon : int

Draw an N-sided polygon shape at each measurement location. Default is 20 (approximates a circle).

Rotation : float

Rotate the N-sided polygon, specified in degrees.

DataSetName : string

Descriptive text that gets embedded into the KML file.

Colormap : string

Name of the colormap used to color the polygons, based upon the data value. Default is “WhiteBlueGreenYellowRed”.

UseLogScale : boolean

Apply a  log-10 scale to map data onto the colormap.

ConstOpacity : float

Opacity of the color polygons, in the range 0 (transparent) to 100 (opaque).

UseConstSize : boolean

If True, polygons are drawn in a fixed size.  If False, the size of the polygon reflects the value of the underlying measurement value. Default is False.

ShowOutline : logical

If True, draws the outline of the polygon. Default is False.

Fill : boolean

If True, color-fills the interior of the polygon. Default is True.

MinData,

MaxData : numeric

Used to clamp the range of values in the measurement data

DataScale : float

Scale factor applied to the measurement data. Default is 20000(?)

Tesselate : boolean

??? Default is True.

AltMode : enum

Altitude-Mode - determines how the extruded polygon is positioned in space. Valid values are: absolute,  clampToGround, clampToSeaFloor, relativeToGround, relativeToSeaFloor. Default is relativeToGround.

Extrude : boolean

??? Default is False.

StoragePath : string

A pathname prefix for the KML output file and PNGs. The default is the current directory.

Verbose : boolean

When set to True, writes diagnostic output to stdout. Default is False.

Example

load "$NCARG_ROOT/lib/ncarg/nclscripts/contrib/NCL_GETools.ncl"

begin

            ;

            ; LOADING DATA

            ;

            Data=read_ict("../ExampleData/Aircraft/mrg60_dc8_20080618_R13.ict")

 

            lat=Data(:,5);

            lon=where(Data(:,6).gt.180,Data(:,6)-360,Data(:,6))

            z=Data(:,15)*1000.0 ; converting to meter.

 

            ;

            ; Getting Time String in the format of yyyy-mm-dd_hh:mm:ss                          

            ;

            YYYY=tointeger(str_get_field(Data@Header(6),1," "))

            Date=jul2greg(Data(:,1)+tointeger(greg2jul(YYYY,1,1,1)))

 

            hh=tointeger(Data(:,0)/3600.0)

            mm=tointeger((Data(:,0)-hh*3600.0)/60)

            ss=tointeger(Data(:,0)-hh*3600.0-mm*60)

 

            TimeTagStr= sprinti("%0.4i",Date(:,0))+"-" \

                                   +sprinti("%0.2i",Date(:,1))+"-" \

                                   +sprinti("%0.2i",Date(:,2))+"_" \

                                   +sprinti("%0.2i",hh)+":" \

                                   +sprinti("%0.2i",mm)+":" \

                                   +sprinti("%0.2i",ss);

            ;

            ; Exporting the Measurments to KML                                                                                                                                          

            ;

 

            Opt@DataSetName="NO"

            Opt@DataScale=10000.0;

            Opt@NSidePolygon=3;

            Opt@Rotation=90.0;

            Opt@UseLogScale=True

            Opt@UseConstSize=True

 

            Measurements2KML("Measurements_NO", lat, lon, z, Data(:,44),TimeTagStr,Opt)

end

 

 

Collect_KMLs

A convenience function to collect several disparate KML files into one.

Prototype

procedure Collect_KMLs(

    outFilename[1] : string

    inFileList[*] : string

    opt : logical

)

Arguments

outFilename

Name for the combined KML file.

inFileList

An array of filenames of KML files to be combined.

opt

Optional resources.

Recognized resources

NameList: string[*]

Optional:  A list of descriptive labels associated with each input KML file.