double-the-distance aiming method (PIM: Pocket Intersection Method)

Dave:
...I think the difference in Don's document (again the diagram and document are not mine), is that everything is referenced to the CB center. Because of this, the proposed method is not "geometrically correct." It breaks down as the CB gets closer to the OB...

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Yes, the system is not truly "geometrically perfect" unless the OB center, contact point and doubled distance are measured through their counterpart positions on the CB (so that the three lines are parallel rather than converging at the CB). This would require shifting the head/eyes as each is sighted - fortunately the error is small at normal shot distances.

This is another argument for centering the contact point between the CB/OB edges for thinner-than-halfball hits and between CB/OB centers for fuller-than-halfball hits - this ensures the smallest "centering area" and smaller centering areas produce smaller errors of this kind (in addition to smaller distances being generally simpler to estimate).

pj
chgo

BTW, that pivot and shift version is not one of the old Double the Distance methods that was discussed.

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It was discussed (I think Bob Jewett described it), but not as "one of the Double the Distance methods". It was rightly considered to be another method entirely. Unlike double-the-distance, this "shift and pivot" method doesn't break down when the CB/OB are close together, but it's also much more cumbersome to use.

pj
chgo

Clark_the_Shark said:

I think the DIM, Ghost ball, Joe Tucker's, and what I am calling the "Parallel Line Aiming Method" (Described in the book "Precision Pool" with Gerry Kanov & Shari Stauch) and described in fine detail here... http://forums.azbilliards.com/showpost.php?p=230576&postcount=37 are all very similar methods. But personally, for hard to estimate shots, or even combos and easy shots, I feel the "Parallel Line" method and/or Ghost Ball method works the best.

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I think this varies for different players with different visualization skills.

The Parallel line method is EXACTLY like Joe Tucker's aiming method except he uses numbers to identify each spot, whereas you don't need any numbers to memorize with this method.

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This is a good example of why different players prefer different methods: some find Joe's numbers easier to visualize; others find the parallel lines easier. They accomplish the same thing but use different kinds of visualization skills.

Very simply, you just take the contact point on the opposite side of the OB (the point CLOSEST to the pocket) and visualize that exact point on the CUE BALL, then drive the point on the cue ball to the contact point on the object ball.

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"Aiming at the OB contact point by feel" could be described with the same words; imagining parallel lines to help locate the CB contact point is the only difference. Again, they accomplish the same thing (so does ghost ball) but in different ways.

pj
chgo

Yeah, true true... just thought I'd add to the 'confusion' heheh.. I guess I'm trying to just put all of these systems together so that people understand we're all pretty much trying to do the same thing but in different ways. Whichever one works for you. People get caught up in the "I have a miracle system" rather than, look at all these methods, they all do the same thing but in different ways.

dr_dave said:

Recently, Don Smith sent me a document describing an aiming system he thinks might be new. I call it the double-the-distance aiming method (d'DAM). He calls it PIM: Pocket Intersection Method. Don asked me to post it and see if people think it is new or not, and to get feedback. I've never seen this presented before, but it is too simple and makes too much sense to be new. Have you guys seen this before in any books or videos? Please give it a try and report back with any feedback or recommendation you might have.

Here's Don's complete document:

"An Aiming Point Method For Pool" by Don Smith, August 2009​

Here's how it works (per the diagram below):

1. Find the point where a line from the cue ball will intersect the object ball.
2. Find the point where a line from the pocket (or other target) will intersect the object ball.
3. Estimate the distance between these two points.
4. Double this distance to find the aiming point.

PIM doesn't work well when the CB is close to the OB, but it works fine when the balls are farther apart, for all cut angles. It does take a little practice estimating the distances, but you can use your cue tip to help. See the document for more info and examples.

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Yesterday, I tried out this aiming system.

I placed an object ball on the foot spot and placed the cue ball one diamond to the left or right of the head spot. After numerous attempts with this setup, I made some balls but mostly missed.

For more distant shots such as what I described above, it's hard to make accurate visual measurements. If L is off by 1/8-inch, then 2*L is 1/4-inch in error, which will affect your aiming point significantly.

FWIW, the following thread is where I first heard about this method...

http://forums.azbilliards.com/showthread.php?t=25185

In that thread, Bob Jewett linked the following articles...

http://www.sfbilliards.com/articles/1999-11.pdf
http://www.sfbilliards.com/articles/2004-06.pdf

do you or others actually use any of this stuff with any types of shots, [NO] or is it more just an interesting collection of geometric curiosities? [YES] It still seems to me that straight ghost-ball might be easier for most beginners, rather than trying to estimate small distances along different lines.

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bingo! ....

Patrick Johnson said:

I'm sure we were discussing it on RSB before the turn of the century. Variously called "double-the-distance", "double-the-overlap", etc. It came up often in discussions of aiming systems because it's one of the few "geometrically correct" systems (like ghostball). It's OLD.

It's so well known that it's illustrated on CueTable.com's Aiming Calculator. Here's a snapshot from it. Notice the red X in the center of the CB/OB overlap (the X is part of CueTable.com's image; I added the red curved arrow and text).
View attachment 107886
Your drawing illustrates doubling the distance from the OB's center to the contact point (and then aiming the CB's center at that doubled distance). The same method also works by doubling the distance from the OB's edge to the contact point (and then aiming the CB's opposite edge at that doubled distance). Doubling from the OB's center is best for shots fuller than half ball; doubling from the OB's edge is best for shots thinner than half ball.

pj
chgo

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Patrick,
Is there any chance you could illustrate the doubling from OB's edge for thinner shots? If it is a lot of trouble, please don't bother but both of these methods interest me a lot.

Thanks,
joeyA

Focus!

PoolSharkAllen said:

Yesterday, I tried out this aiming system.

I placed an object ball on the foot spot and placed the cue ball one diamond to the left or right of the head spot. After numerous attempts with this setup, I made some balls but mostly missed.

For more distant shots such as what I described above, it's hard to make accurate visual measurements. If L is off by 1/8-inch, then 2*L is 1/4-inch in error, which will affect your aiming point significantly.

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While I haven't confirmed your theory about your aiming point being affected adversely (I'm sure you're right), there is another VERY IMPORTANT thing about all aiming systems that is probably underestimated by some of us.

When using virtually any aiming system, most people are really "paying close attention" to what they are doing. When you pay close attention to what you are doing you focus better. I watch the pros playing in the big tournaments, guys like Archer, Stevie Moore, Charley Bryant, and dozens of others who pay "extra attention" on particular shots and the extra attention apparently pays BIG DIVIDENDS.

imo, the best things about Aiming systems is that they help your eyes and mind to pay closer attention to what you are attempting to do.

JoeyA

Thanks guys, this is good stuff.

my 2 cents.

I love all the inputs we are getting over the last few weeks.

But perhaps we are looking at this the wrong way. I don't think we can look for a perfect aiming system in the context playing a game pool against an opponent.

Meaning, in certain situations, we need to add english, which shifts the contact point. Sometimes the balls are closer, which makes it easier for the ghost ball method to work, etc.

Personally, within the last week, thanks to all the inputs on the forum, I was able to become a VERY very good shooter.

There is this gentleman that I play on a regular basis. He is an APA 6. I am a 3~4. He used to beat me 5 games out of 6.

This week, in one week. the tables turned where I was beating him 4 games out of 5.

The secret to my success had 2 parts and it was unconventional at best.
1. 15 ball rotation practice by myself(mainly b/c I heard Efren used to do that). When I played a APA 9 on a 9Ball game I was actually relieved to see so many fewer balls on the table. I beat the APA9 on a few racks. And I am an APA 3~4.

2. I was aiming at different parts of the pocket. even at the pocket edge point, sometimes an inch outside of the edge of the pocket...

All depending on if I was using english, if there was throw, cut angles, etc.

It was funny b/c one seasoned player noticed my sudden improvement in skill and talked to me to see if I had a coach. I told him nope, I am not aiming straight at the pocket on non straight shots.

This is the funny part. He was like NO NO NO. He grabbed the 9 ball and used the 8 ball as the ghost ball to show me where to aim it, ON A CUT SHOT, where some throw was involved.
He said "Make a straight line through the pocket, the 9 ball and the 8 ball." But BECAUSE he has played for such a long time he instinctively placed the ghostball aimed at the edge of the pocket. Before he took a closer look he sweared that he has set up the pocket, 9 ball and the 8 ball in a straight line.

I been on a tear this week. Even few racks running the last 6~7 balls against APA 8 and 9s.

Thanks AZ and all you guys.

JoeyA said:

Patrick,
Is there any chance you could illustrate the doubling from OB's edge for thinner shots? If it is a lot of trouble, please don't bother but both of these methods interest me a lot.

Thanks,
joeyA

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Joey, I can't do any illustrations right now, but if you look again at the picture of CueTable.com's Aiming Calculator that I posted in post #32, you'll see that the contact point is centered between the CB/OB centers and their edges. This is always true; you just have to realize it to use it.

I plan to post some drawings that I hope will make things a little more clear about this sytem, but that will have to wait a few days.

pj
chgo

Patrick Johnson said:

Joey, I can't do any illustrations right now, but if you look again at the picture of CueTable.com's Aiming Calculator that I posted in post #32, you'll see that the contact point is centered between the CB/OB centers and their edges. This is always true; you just have to realize it to use it.

I plan to post some drawings that I hope will make things a little more clear about this sytem, but that will have to wait a few days.

pj
chgo

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THANKS!
joeyA

I was curious to see how great an error Don's method produces. It does seem to get you pretty close on most shots. Below are three plots of the errors in impact direction at three different CB-OB distances, measured center to center. I included the 8" separation out of curiosity, but he explicitly recommends that special adjustments be made whenever the balls are less than 15" apart.

The horizontal axis is the intended impact angle, with divisions of 5 degrees. This is the desired OB direction with respect to the CB-OB line of centers. The vertical axis is the error in degrees, and each division is 1 degree. The curves come to an abrupt end on the right, where a greater than 90-degree cut angle would be required to increase the impact angle. (The corresponding cut angles, not shown, are always larger than the impact angles.)

Most of the errors are undercuts until you get to extreme cut angles (where the red curve crosses the horizontal axis). Overall, it looks pretty accurate, but anyone using this might want to do some tweaking, especially in the 25-55 degree range, which I think he also suggests.

8" CB-OB Separation:



17.5" CB-OB Separation:



36" CB-OB Separation:



The geometry would be perfect if you moved the plane in which you "double the distance" forward or backward, so that it intersects (includes) the center of the ghostball. But then of course, you might just as well aim at it! Obviously, that wasn't his intention.

Thanks as always for making this available Dr. Dave.

Jim

dr_dave said:

...The errors are worse than I thought they would be.

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As you probably could tell, I had more or less the opposite reaction, but I'm not arguing. (I say that despite the next paragraph?)

dr_dave said:

This is the problem I have with the traditional "geometrically-consistent" "double-the-distance" or "center-the-contact-point-in-the-parallel-projection-ball-overlap-lens" aiming methods. For them to work properly (i.e., to be "geometrically consistent"), you need to know where the ghost ball center is.

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That's one reason I'm glad you brought it up, along with the general discussion that ensued. Having never given it much thought, I sort of assumed that it was geometrically equivalent to ghostball aiming, without regard to which plane the "doubling of the distance" was performed. Live and learn.

Jim