Entity
GeomagneticModelData
GeoGraphics
GeoPosition
GeoDirection
GeoDisplacement
GeoDestination
GeoProjection

Geography

Chart the Northwest Passage

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Use geomagnetic modeling to plot differences between magnetic and true north at high latitudes

Begin with a list of latitude-longitude pairs describing the Northwest Passage along the coast of North America:

In[1]:=

course=

GeoPosition[

]

;

Obtain the position of geomagnetic north, using

GeomagneticModelData

In[2]:=

geomagneticNorthLocation=GeomagneticModelData["NorthGeomagneticPole"]

Out[2]=

GeoPosition[{80.745,-72.6787}]

Show the Northwest Passage together with the position of geomagnetic north on the map:

In[3]:=

GeoGraphics[{{Red,PointSize[Large],Point[geomagneticNorthLocation]},Line[course]}]

Out[3]=

Navigating the Northwest Passage using a traditional magnetic compass is challenging due to large differences between magnetic and true north at high latitudes.To chart the Passage and obtain current magnetic field data for the Earth, define a function that can be used to plot the direction to the geomagnetic north pole (in red) and local compass reading (in blue):

In[4]:=

bearings[point_]:=Module[{d1,d2,distance=

400

,h1=GeoDirection[point,geomagneticNorthLocation],h2=GeomagneticModelData[point,"Declination"]},{d1,d2}=GeoDestination[point,GeoDisplacement[{distance,#}]]&/@{h1,h2};{Red,Arrow[{GeoPosition@point,d1}],Blue,Arrow[{GeoPosition@point,d2}]}]

Pick a reasonably well-spaced set of sample points:

In[5]:=

samplepoints=course〚All,{2,3,4,7,11,13,15,17,19}〛

Out[5]=

GeoPosition

Number of points: 9

Lat bounds: {62.3,74.4}

Lon bounds: {-168.,-58.5}



Determine the magnetic declination of the sample points:

In[6]:=

GeomagneticModelData[#,"Declination"]&/@Thread[samplepoints]

Out[6]=

{

-29.0405

-35.2352

-20.7833

13.0232

19.8356

18.6074

11.7938

6.79611

7.09751

}

Show the differences between true (red) and magnetic (blue) bearings along the Passage:

In[7]:=

GeoGraphics{{Red,PointSize[Large],Point[geomagneticNorthLocation]},Line[course],bearings/@samplepoints〚1〛},



Out[7]=

Related Symbols

Entity
GeomagneticModelData
GeoGraphics
GeoPosition
GeoDirection
GeoDisplacement
GeoDestination
GeoProjection

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Contributed by: Wolfram Staff

Wolfram Language Example Repository

Chart the Northwest Passage

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