Block Distance Calculator: input the X Y Z while standing in one spot, move to another spot and input those X Y Z coords, then click calc and it tells you how many blocks are between the two points. It works diagonally, sideways, up and down, it doesn't matter, the equation even works with positive and negative values.
Note: the TOP button keeps the window on top of the Minecraft window to make it easier to read and input the X Y Z.
Note2: This is a stand alone jar file, meaning, its not a plugin, meaning you DON'T have to put it in Minecraft.jar
Story of what lead up to me writing this app and why I needed it:
So, there I was building a typical zombie drop damage XP farm and I had gotten to the point where I could stand within 16 blocks of the spawner and hear the zombies spawn and fall in to the water and make their way down the tunnel toward the drop off; I even put a few glass blocks close to the very end of the drop off tunnel so that I could see that they were spawning and moving correctly through the tunnel.
BUT, when it came time to go down the ladder to where the zombies were being dropped (the kill/XP collection spot), there seemed to be much fewer zombies than I had seen go through the tunnel. AND there ACTUALLY WAS fewer zombies than I had seen go through the tunnel. The reason why, wasn't because the drop was too high and that they were dieing when they hit the ground, it was because I was outside the 30 block range that you are required to be within to prevent mobs from despawning after roughly 30 seconds.
AND, since I hadn't built the point where I wanted to stand in a straight line along with the collection point, so that I was BOTH in the 16 block range of the spawner so that it would be active, AND within the 30 blocks of the collection point so the zombies wouldn't despawn; I was stuck trying to figure out how to figure out how many diagonal blocks (diagonal along all three axis) that I was away from the collection point.
At first I tried to do the math myself, guessing as to what equation I should use. I got pretty far and was on the right track, but then I decided to search for an equation that someone had already thought of where I could just input the X Y Z for 2 points in 3 dimensional space. That worked great, BUT, it required that I sit there with note pad and calculator open; and doing the equation has more than a few steps where you have to write down or remember the particular values in between steps. (well, just using regular old notepad and regular old calc anyhow.)
SO, basically, doing it that way was a major pain in the head, so I wrote this, so, now all I have to do is input the X Y Z for the 2 points where I need to know the number of blocks in between and hit the button. (so, so, so, so so so so ,it didn't have enough so's)
As a side note, My idea of the ideal survival zombie spawner. (which is mostly why I thought having an easy way to figure out how many blocks I am from another block without too much thinking involved was worth all this effort)
1. Basic drop damage and spawner block setup.
2. Hopper with chest on the drop point.
3. 1 shot all the zombies with splash health ii potions (and be blinded with XP orbs for a good few minutes)
4. THIS IS THE IMPORTANT THING: a potion brewery/afk room that sits within the 16 block spawner range AND the 30 block despawn range, so that you can stand there and brew potions and have something to do/get up and go make a sandvich (DON'T RUN!! IT'S JUST HAAAAMMM!!) and know that your character will be safe, while you wait for zombies to add up.
5. Semi important thing: a mine cart track that transports you (and mine carts with chests in them full of splash health II potions) back and forth between the brewery/afk room/active spawn radius and the XP collection point. I suppose you could put a hopper and a collection chest on the very last block of the transport system. And, I suppose you could also put a call button up by the brewery; so that when you think the mine cart chest full of potions has been emptied, you can push the call button and the empty cart will return to the brewery.
This video was originally just a random/misc video I made, but since it demonstrates the zombie drop damage xp farm and since I don't want to re-upload what would just be a smaller part of a larger video I already uploaded, I'm just going to embed that video instead. The video also includes my dark room drop damage over world item farm design too.
The zombie spawner thing is at about 9 mins.
If you think you might find this useful, you can download the .jar file from my mirror site.