Is there a simple tool to change Terrain?

[fuzzy]

I want to create an island that from above looks like a particular shape, but obviously it would take me a long time to build it by hand. I am wondering if there is an easy way to do this in game in a way that:
A) makes it take less time
and
B) make sure nobody destroys it

[Wuzzy]

For A there is WorldEdit and of B there is a wide range of protection mods, just look a bit around the mod forums and choose one which fits your needs best. I do not have much experience with protection mods, so I cannot recommend any particular protection mod.

WorldEdit:
viewtopic.php?f=11&t=572

[twoelk]

you might want to try the Image Loader Mod from Kaeza to import the outlines. Take note though that you get a flat result. You cannot import any sort of hightmap this way.

For large scale editing WE (WorldEdit) is really the best there is at the moment as that mod has many usefull features. WE will not help you to randomise the Landscape a little to make it look less geometrical though. So you will need some landscaping skills and enough time to create convincing terrain.

You could search for the old nodegun tool. It is quite usefull to add blobs of nodes here and there. I think it was in the Riven subgame. Might have been somewhere else though and might not work with the current version of Minetest.

Paramat wrote a Landscaping by command mapgen mod. I am not sure how much control you have over the terrain creating details though.

A much more complicated sollution would be setting up a toolchain of several programs and scripts.
First use the Worldpainter to create a map.
Export the result to a Minecraft map (yes that other voxelworld game)
Install this MCEdit filter script
into an installation of MCEdit.
Open the Minecraft map with MCEdit (you do not need any Minecraft installation for this!) and use the script to convert the part you need to a Minetest schematic file. Take note not to make it too large, or you may not be able to open the file later.
Create an Minetest map to your liking, for example take the flatgen mod and create a map of water.
Open the map with the WE mod installed and import your schematic file of the island.

For the import process you may also want to study this thread: Converter Minecraft world to Minetest world

If along the way you come up with an easier sollution, be sure to report about it in the forum.
good luck

[paramat]

If the island is to be formed in a new world you could use using my 'archipelago' mod, replace the noise-defined sinking of terrain with mathematics that lower terrain below water over a large area apart from a mathematically defined x shape.
I guess ideally a new version of archipelago which sinks and blends mapchunks of terrain by chat command, try combining my 'archipelago' and 'nysauto' mods. I'll leave that to someone else to atttempt.

[bobomb]

Realterrain mod. you can paint a grayscale heightmap and use that as the source image for the map. viewtopic.php?f=11&t=12666

to keep things simple you don't need any libraries, but save your BMP as RGB mode even if you are only painting grays. Also some paint programs save headers that the mod can't use but it has been tested with photoshop. Photoshop is not recommended for painting the biomes though since the anti-aliasing is unwanted... this mod will do much more than you are asking, but it will do what you are asking easily. Create your file in the rasters folder of the mod, take the Realterrain Remote in hand in the game, change your elevation raster to that file, click "delete" to destroy the world already generated and then relaunch the game and map. once your map generates, you can disable the mod and the world will persist.

if someone destroys your island, just redraw it in the same way from the same source image. if you want buildings that you have placed on the island to persist, there are tools in the mod to do that too.