HELP!: Polar Stereographic Maps

[OBK!]

I have just started ground school, distance learning and came across the topic "maps and charts" but I'mjust blown away at the stuff about polar stereographic maps. What are they all about?! Any help would be much appreciated.

['%MAC']

As you are well aware, distortion results any time you project a curved surface on a flat plate. Polar Stereographic Charts (we don’t use maps in aviation) are conformal, with a nearly constant distance scale. The distortion increases as one moves away from the pole, meridians are straight lines radiating from the pole, while latitude is depicted by unequally spaced concentric circles (Polar Gnomonic Charts have equally spaced concentric latitudes). Polar Stereographic charts are used for all types of polar navigation, while PGCs are used for great circle navigation and planning. A grid zone has been developed for polar navigation and is known as the Universal Polar Stereographic Grid Zone. But we really don’t want to get into grid navigation without visuals. Best of luck on your studies.

[mikef]

If my memory serves me correctly Polar Stereographic Charts are taken imagining that a "photo" of the earth is taken from a point above either of the poles. If you can imagine this, the lines of longitude should be staight and lines of latitude should be circular. I'm not sure how far you are into your training but with these maps, straight lines are great circle tracks and therefore the shortest distance between the two points. Lines that follow the lines of longitude or latitude are rhumb lines.

Hope that helps. I haven't come across many of these charts in my time. I think most of the charts used in aviation are mercator charts which are a bit different again.

[compressor stall]

How far away from the north/south pole do you stop using polar stereographic maps?

(or conversely at what latitude do you stop using WAC or ONC charts??

[Notso Fantastic]

As in mikefs description (well put), you have to transfer your 'photo' information from a curved surface (world) to a flat plane (a map). So if you imagine a flat plane held against the Pole and the information falling straight onto this plane to give you a 'map'. But, as you go further from the Pole, you will get increasing errors because of the Earth's curvature. So here's the clever thing. Instead of putting your plane touching the Pole, put it vertical to the Polar axis still, but through the Earth passing through a latitude say 85 degrees. That way, you will keep your distortion to within a certain band, right to the Pole, and further away from the latitude selected, thus vastly increasing the area of the map useable and within a particular distotion figure.
Using thse maps is quite confusing to begin with. Atlases always use Polar stereographic projections of the Poles. You have to remember distortion increases away from the Poles.
I always found cartography one of the most fascinating studies- something I would have loved to continue in an alternate career! But it can get fiendishly complicated.

[earnest]

The European Jeppesons and trans-Atlantic plotting charts are Lambert Conformal (conical projection), which are similar to Polar Stereographics in that straight lines = great circles etc.

Where are mercators mainly used?

[Notso Fantastic]

The expression 'Lambert's Conical Orthomorphic' springs to mind. I think that may be a Lambert's Conical projection, but through the Earths surface rather than tangential to increase the area of accuracy. Similarly Mercators, which is probably the most distorted map projection of all, may go through the Earths surface rather than be tangential to it. Mercators are heavily used for wide mapping displays of the Earth and make for simple though distorted displays in atlases . Imagine a cylindrical sheet wrapped around the Equator, with a light at the centre of the Earth creating the 'projection'. The higher latitudes get really distorted, the lines of longitude become straight vertical parallel lines. Distortion becomes intense at higher latitudes hence Greenland can appear bigger than Australia- don't even ask about the Poles! These are heavily used in basic atlases. For a well travelled route like London-Sydney, you can have a 'leaning over' Mercator with the Great Circle between the two being the line where the projection touches the surface. Lovely accurate chart for that route, but the lines of latitude and longitude will do bizarre things as you move on the route. Mercators are also good for plotting charts of the North/Central Atlantic, but you have to watch your scales as they change vertically a lot.
It's a fascinating subject. Nobody realises how intensely complicated this whole business of map projection is- the art of putting a 3d surface onto a 2d bit of paper. Every page of my Philips Concise Atlas tells you what projection is used: Lamberts Azimuthal Equal Area, Sanson-Flamsteed's Sinusoidal, Lamberts Conformal Conic, Zenithal Equidistant, Conical Orthomorphic with 2 standard parallels.......wonderful stuff! OBK- enjoy this part of the course- sure as hell beats Aviation Law!

[No_Speed_Restriction]

Better yet OBK!, What question/s have been thrown your way?

You'll find Polar chart questions require much less use of the calculator especially if you are given Grid problems as Convergency=Chlong.

[mad_jock]

For some unknown reason they are in 2 sections. Gen Nav and OPs procedures. French didn't trust the germans to test them properly

MJ

[No_Speed_Restriction]

fair enough.
If you do have a specific question though, fire away.

who knows, I might even give you a correct answer :yuk: