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From: George <georvisc@...>
To: OccultNEUS <[email protected]>
Date: Friday, 17 November 2023 6:51 PM EST
Subject: Re: [OccultNEUS] Occult4 201

Steve:

I strongly suspect that the following is your issue.........

In order to do a "deep search" (meaning, involve a LOT of asteroids in the search), they have to be in your database === to begin with.
There are 3 asteroid databases that Occult4 needs to load. they are:
* Astorb --- from Lowell Obs
* ASTDyS-2 --- from Europe
* MPCorb? --- from the MPC
These are accessed from the Main Page --> Maintenance --> General Downloads
When you update your databases (which should be done every couple weeks or so), you come to a "Convert" stage (see attached image).
At the Convert stage (for each above database) you tell Occult4 some limitations in what you want included in your Occult4 searches. One of the options is the minimum size in km of the asteroids you want involved in your Search. Here I use 3km. If, for example, you wanted Occult4 to only Search down to a minimum size of 10km, of course, you would put 10km here. If you input "10" here instead of "3", the amount (number) of asteroids used in your Search(es) will ["always"] be less.
Convert "builds" the [single] asteroid database that Occult4 uses in each Search from then on.
My guess is in the Convert stage, the "minimum size" you have is larger than 3km.

The following is an excerpt from what I previously posted under the Occult4 101 topic. It tells you how to update the 3 databases and -- if you want -- you can try entering in 3km when you do the 1st "Convert". Occult4 will remember your setting for the other 2 databases.

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So now go to download #23 Astorb....
When you select Astorb, it should download. Upon completion of the download, you are taken to the (same) Convert window. What "Convert" does is reads the Astorb file and converts it into a format that Occult can use.
At "Convert" several things show.... (as in your image)....
* Include MPs larger that "X" km. Here I use 3km. But as you know the smaller you go, the numbers increase 'exponentially'. You could try 3, but maybe to start you might try 5 or 6 (you can change this later). [You can revise the diameter setting the next time you update the 3 database files].
* Numbered MPs only (I leave this unchecked).
* Limit to 3+ oppositions (I like this checked). If unchecked the additional asteroids that will be included will have very large uncertainties (ie., huge 1-sigma bounds). Good Luck getting an occultation on those!
*"Mandatory MPs.." This means, no matter what, I want the numbered MP(s) to be included in my database - irregardless of any above specified setting. For example you might want to include some of the Near Earth Asteroids that IOTA likes to go after --- like Phaethon, which are under 3km. You don't have to enter any additional numbers here, but if you don't add some small, important ones, they will NEVER show up in your Occult search (as they simply won't be in your database).
--- After you configure what you want, then you press the "Convert" button. Convert builds a subset of Astorb in a file format that Occult can use.
It should then show you a folder where Astorb is stored. Accept this by clicking "Open". ("Open" overwrites any older file).
You will see a "Convert" progress bar and it should eventually say "Astorb conversion complete".
Next, you do the exact same steps for AstDyS-2 (Convert should remember your selection settings), it will show you the folder where AstDyS-2 is stored, you press "Open", and it should say ASTDyS-2 conversion complete.
Lastly do the same thing for MPCOrb.

The reason you load these 3 files is that none of the asteroid database files contains all the info that Occult needs to make a prediction. For example, MPCOrb does not contain any info on the uncertainty of the orbit - so the 1-sigma uncertainty lines could never be generated from MPCOrb. Nor does it contain info on the asteroid's assumed diameter. So in short, Occult has to draw from all 3 databases to get all the info it needs to properly make a prediction.
Now, why you do MPCOrb last.........
I may be wrong on this - as it's been years since I tried otherwise - but I believe that the last database file you load is the one that Occult uses for the actual orbital elements (All 3 files? contain orbital elements, tho they may be slightly different!). For example, if you load MPCOrb last, your initial "Search" will be based on the orbital elements in MPC's MPCOrb.
You can see the orbital element database that Occult uses - as it's just to the right of the "Search" button when you start a search.

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We'll do a Zoom session on Occult4 sometime the week of Nov 29 - Dec 1 - at a time when everyone can attend.

? -G