Dodgy Latitude & Longitude Markers hints please...

[abrahadarba]

So I'm working on a planetary atlas...

the thing is, I want to put latitude & longitude markers (on a separate layer in Illustrator) where the 'north pole' is placed at the top of the map approximately a quarter of the way in from the top left corner of the image, and the 'south pole' in a similar position around the bottom right of the image. This would cause the equator to be placed on an angle to the map image itself, but I'll be buggered if I can even find (okay, after a merely cursory search) an image online with a similar graphic. Any smarty-pantses out there that can 1: figure out what I'm on about and 2: give me an idea on how to achieve this? I'd like to do it in Illustrator, but I'm not averse to the concept of using (free) alternate software...
If I can find an image online to use as an example, I'll edit the post to include it.

Cheers

[Azélor]

What map projection are you using? http://en.wikipedia.org/wiki/List_of...ns#Cylindrical

It look like your using this but rotated at 45 degrees : http://en.wikipedia.org/wiki/Adams_h...are_projection

[abrahadarba]

close, Azelor...

but I think the type of projection would be closer to an Eckert VI http://en.wikipedia.org/wiki/Eckert_VI_projection, with the 'prime meridian' warped into a shallow S curve (if that makes any sense) - I swear I saw an image on Google that looked spot-on for the type of projection I was thinking of...

thanks for pointing me at Wikipedia - I might find a closer approximation there somewhere (even closer yet - a Sinusoidal projection, but again with the poles displaced toward the west (for north) and east (for south)

[Azélor]

You did mention that the pole was a point? If you go with a cylindrical or pseudo cylindrical projection, the pole is the top parallel, so it's in fact a line.

[Hai-Etlik]

You are after an oblique projection. Cylindrical, Pseudocylindrical, Conic, and Polyconic projections and most of the hybrid projections derived from them are typically in a "normal" aspect where the projection surface is curved around the planet's axis of rotation (The map wraps around the equator or another parallel). Sometimes cylindrical projections are also used in a "transverse" aspect where the projection surface is curved around a line through the equator (The map wraps around the poles). Anything else is an "oblique" aspect.

Generally oblique projections are used when you have an area of interest that runs over an elongated extent that doesn't run north-south or east west and is big enough that a specific projection is warranted rather than just using the local UTM coordinate system, but also not so big that a global map projection is best. Global maps in oblique projections are almost invariably diagrams meant to explain oblique projections.

This is a fairly arcane ability for GIS software. Proj.4 supports generalized oblique transformations, but most of the software built on top of it like GDAL/OGR doesn't use that capability except in a few constrained cases.

[abrahadarba]

An oblique projection sounds the closest to what I'm trying to achieve so far...

to clarify, the north & south poles will sit inside the image by maybe 2-4% of its total height, and with the equator on a diagonal to the image plane, so that the whole map 'wraps around' on an angle, with a fold-over effect occurring near the polar regions (I have yet to take into account areas of overlap on warping the plane into a sphere, but it might work)

Here's a link to the ocean layers & landmasses for the curious, a test & commentary
http://abrahadarba.wix.com/ganavi
Apologies for the crudity of the page: I started working on it, then dropped it for more constructive progress ( I need more images for the site before it becomes anything near presentable)

[gilgamec]

Here are some oblique projections of the Earth:
An oblique Eckert VI:

An oblique sinusoidal:

An oblique Mercator:

Is this the sort of thing you're looking for?

EDIT:

the north & south poles will sit inside the image by maybe 2-4% of its total height

How about this one? It's an Eckert VI again, but less oblique (so the poles are still pretty close to the top):

[abrahadarba]

yep, that last one (post-edit), please...

the sinusoidal looks a bit too contorted, but the less oblique projection shows the poles roughly where I want them placed on my wip - now I just have to figure out how to go about creating such a layer on top of the map: CAN this be done in illustrator, or should I be looking at other software as well (for 'post-processing', as it were)? Big shout-out to Gilgamec for that rummage of images - my gratitude is (like the universe?) unbounded, but finite

[gilgamec]

I've attached a bunch of PDFs of the graticule: every 5, 15, 30, and 90 degrees, plus a PDF version of the last image in my last post. Illustrator should be able to load these straight in, and you can change the stroke to whatever you need. Let me know if this helps!

[abrahadarba]

cheers once again - I'll have a look and see if I can get the layer integrated.