Shifting an equirectangular map north/south

[acrosome]

Here I have a fine world map:

Sypherion_Final_Texture_small.png

It is Venus, churned through Wilbur and rotated 180 degrees (for reasons).

Let's say that during the terraforming process the planetary engineers stopped Venus's rotation, and then later re-spun it but on a slightly different axis. Is there software out there that will let me manipulate this image to change the axis of rotation? Sort of shift everything north by 15 degrees, while appropriately deforming things to keep the equirectangular projection?

Actually, I would want to do this with the original Venus grayscale heightmap. But is there a straightforward way to do this?

[Mouse]

I don't know this for sure, so please don't kill me if it isn't possible, but I think you may be able to do that in NASAs GProjector.

If you haven't already got it, its here.

[Hai-Etlik]

I don't know this for sure, so please don't kill me if it isn't possible, but I think you may be able to do that in NASAs GProjector.

If you haven't already got it, its here.

No, G.Projector can't do oblique projections. GDAL should be able to do it but it'll involve learning how to set up a custom oblique projection in Proj.4 syntax.

The energy requirements for altering a planet's rotation like that are up in "if you can do it, you don't need to" territory.

[rdanhenry]

The energy requirements for altering a planet's rotation like that are up in "if you can do it, you don't need to" territory.

Venus rotates extremely slowly. Stopping it and starting the new rotation on a new axis would be less work than the inescapable need to spin it up to something much closer to an Earthlike rotational rate or Earth-based climate models won't even apply in the first place, as day/night would easily dominate over seasons.

[acrosome]

Venus rotates extremely slowly. Stopping it and starting the new rotation on a new axis would be less work than the inescapable need to spin it up to something much closer to an Earthlike rotational rate or Earth-based climate models won't even apply in the first place, as day/night would easily dominate over seasons.

I'm all over it, Brother.

[Azélor]

Venus rotates extremely slowly. Stopping it and starting the new rotation on a new axis would be less work than the inescapable need to spin it up to something much closer to an Earthlike rotational rate or Earth-based climate models won't even apply in the first place, as day/night would easily dominate over seasons.

Yes but no since he said he speeded up the rotation of the planet to have a 24h day.

[Azélor]

Stopping the rotation of the planet would destroy everything on the surface except the landscape.
They might not need to stop the planet to change the axis.

[Charerg]

Actually you can shift the continents northwards 15 degrees with GProjector while preserving their shapes. Just pick the "Equirectangular Oblique" and set the center at -15N.

Looks like this for Earth, as an example:
Untitled map.png

I assume this is what you wanted to do?

Edit: I should clarify that this shifts the "center of the map" to -15 N (aka 15 S), so if the "center" is located at 0 E (over the Atlantic), then areas around the Pacific will actually shift southwards (see Alaska and Eastern Siberia in the example map).

[acrosome]

I assume this is what you wanted to do?

Yes! That's what I wanted to do! Awesome. (I already have GProjector, actually, I just didn't know it could do that.)

EDIT--- But, dammit, the largest image that GProjector will export is 7500 px in the longest dimension and my original is 8192 px. I'd hate to lose the resolution.

[Azélor]

It doesn't preserve the latitudes. It bends.