cubiomes-viewer
More info about how Jereaux found the seeds (as he told me), as well as the cubiomes-viewer settings he utilised to isolate the sinkholes:


1. Searching weirdness in cubiomes-viewer is very easy, with one unfortunate small caveat. Weirdness is one of the values that you can use a slider to select the scale of wierdness you want to search against based on your query. To do this you add a Biome condition type, and then select "Climate parameters 1:4" to see your options for searching against weirdness. There are two types of searches you can do against this value and for the most part it's always looking at a range of values.

The first is a "Required" search. For this, when you change the slider you can tell the game that you want to look for weirdness to enter any of the range that you select given the area you are searching against. So if you pick a range from -1000 to 1000, when the engine processes a search against the seed and the area size you are searching against, it must find just a single instance of weirdness anywhere from -1000 to 1000 in that area.

The other type of weirdness search is a "Confined" search. This means when you search against a range, the entire area that you search must meet the range you define. In this case if you are looking at a 100 block wide area and searching -1000 to 1000, a single instance of weirdness outside of the -1000 to 1000 range will fail this check and exclude the seed. That whole 100 block wide area must all fall between -1000 and 1000 weirdess (this is checked every 4 blocks which is notated by the condition type name "Climate parameter 1:4").



cubiomes-viewer How to use it? cubiomes-viewer

2. The primary way to use cubiomes-viewer to search for a seed like this is to tell it to look for any single block area that has weirdness below -19000. This is where the caveat to my original statement comes in. Right now, the cubiomes-viewer user interface will only allow you to select a range starting at -9334 down to -inf. Meaning if I set everything to the lowest search values the UI allows me to, it will pass the check for a seed anytime it seeds a weirdness value below -9334. To get around this limitation, I did some editing of the save files to force it to search against the lower weirdness values I wanted. Essentially in the save files, there are condition lines that represent what you have selected for your conditions in cubiomes-viewer. The simplified way to explain the editing is every 8 characters represents a different value for a different condition type in the UI, and the whole long string represents every value that can be changed. I found the area in the conditions line that represented weirdness, and edited the values to be what I wanted it to. So for weirdness instead of searching -9334 to -INF, I set it to search -19000 to -23000.

So that single search element does allow me to search for these dips in the land, however it is fairly slow. I added two additional conditions to make the search faster and allow me to search a wider area for these high weirdness values. The "Reference Point 1:256" conditions allows me to have cubiomes-viewer center a search against a bunch of different points every 256 blocks instead of just a 0,0. Then I set my 2nd search condition to do a "Confined" weirdness search for a very small area every 256 blocks to look for weirdness below -13k. So it creates a grid kinda like this one where every point listed on the grid, cubiomes-viewer is looking at each of those points and making sure at least one of them has below 13k weirdness. If that passes, then it looks at the whole area to see if any point anywhere on the grid has -19k weirdness.




3. Once I had my list of seeds, I did go one by one and check each one against the depth chart to see if a low area generated. In the first seed I'm hovering my cursor over the black area just south of spawn, and it shows me a depth of -6749. This should generate a fairly large sinkhole though maybe not the best. The next seed has a depth a -7896 which should generate a large and very deep sinkhole. I would also look for seeds where villages or other structures generated over the sinkhole. The third seed does not have a large dark area, and generally I would just skip over these. However I did learn that sometimes the sinkhole would not generate in the normal vanilla seed generation, but would in large biomes. So I check the large biomes box to see if it generated there. If so, it gives me another potential seed to look at (the 4th picture is the same seed as the 3rd, but with Large Biomes checked).

cubiomes-viewer PasteShr cubiomes-viewer
Once I found seeds with good depth values, I would copy and paste the seed into chunkbase with terrain view on. This would allow me to search against Bedrock structures to see if anything would generate in Bedrock as well. I probably skipped over 1/2 or more seeds looking at cubiomes-viewer depth chart as either no low area generated, or it was not very deep. Then I pasted all those into chunkbase and filtered down to the list of seeds I wanted to check in game. I don't recall but I assume I logged into 100+ seeds for this search, probably approaching 200.

Creating the seeds in Bedrock is slow and I didn't log into most of them that way. I probably checked 2 dozen or so in bedrock. In Java, Crackedmagnet created a seed finding mod that makes checking seeds WAY faster than having to generate a whole new seed every time. His mod allows to jump into new seeds by essentially treating them like other dimensions of the same seed you are in. So instead of sitting at a long loading screen, it takes about as much time to generate a new seed as it does to go to the nether in a normal seed. He created a new world type called "Seed Finder" and once you create a seed using this type, it gives you a bunch of additional in game options for searching seeds, and loading into new seeds.

crackedmagnet's seed finding mod - https://www.youtube.com/watch?v=tGb5G22_7kk 
cubiomes-viewer