Distance estimation [Archive] - TradTalk Forums

: Distance estimation


Greysides
06-19-2010, 02:11 PM
From the FITA Field Archery Guidelines (http://archery.ie/field.pdf):

In Field Archery an important part of the shooting technique consists of making accurate range
estimations on the unmarked courses. In order to compete with the best archers this knowledge
can not be entirely dependent on your intuition or on your terrain evaluation, as these methods
are far too inaccurate and you will end up losing too many important points. A field archer will
have to find his own way to appreciate the distances, and he will have to practice this as part
of his shooting form. The most accurate methods are based on geometrical concepts as shown below.

Most of the methods, if not all, are based on the application of the Thales Theorem, by which we
can find the wanted distance if we know the distance from the dominant eye to a measuring
item (i.e. sight ring, scope, arrow rest, etc) placed on the bow, called d, which width is
called a, and the width of the projection of that item on the target as you see it, or which can be
calculated (the size of what you see on the target), called A. The relationship between these
elements will give you the distance to the target, called D, by simply applying the relationship :

a / d = A / D


Using as a measuring item any permitted part of the equipment, as for instance a sight component,
the arrow rest, etc.
In order to make it easier to understand, and to avoid the need to be applying any mathematics
on the field course, and in order to get the distance to the target as simply and quickly as possible
use the following principle; If the width of the measuring item (i.e. sight ring etc) happens
to be exactly one hundredth of the distance from the retina of your eye to the measuring item (i.e.
the sight ring is 8mm and the distance from the eye to it is 80cm) or if you can adjust your equipment
to make that relationship , then the relationship will be :

D = A * 100

Which if taking D in meters, and A in centimeters, will become : D (metres) = A (cm)

So that the range (in metres), D, results from the simple calculation of the measuring part's projection
width (in centimeters), A, on the target.

The knowledge of A is based entirely on the assumption that we know the target size. For
instance if the target on the figure is an 80cm diameter face, A would cover half of the face,
plus one division and a half, that is : 40+8+4 = 52cm, and we would conclude that the distance
to the target is 52 meters. If on the other hand it was a 60cm target face, then the calculation
would be : 30+6+3 = 39cm, and the distance 39 meters based on the above mentioned relationship.

This simple and immediate relationship is not always possible, and then the archer needs to
find his own. However, most archers do not apply any maths when doing the measuring,
they simply compare by experience based on the described principle.

http://img59.imageshack.us/img59/7664/targetcomparison.jpg

For instance, when practicing you will shoot from various distances on the various target
face sizes. By practice you will find how much of your sighting device, or anything else, you can
see in front of you, is covering the target face or buttress.


Hopefully you can follow that. Essentially I used the Thales Theorum part of it.

To cut a long story short, I hold up the bows sight window against one edge of the target and see how many rings are obscured (taking it as 10 rings per target).

With a 20 cm face each ring covered adds 1.2m to the distance from the target.At 12m the width of the face is completely hidden.
Unmarked FITA distance with this face 5-10m.

With a 40 cm face each ring covered is a 2.4m to the distance from the target. At 24m the face is completely covered.
Unmarked FITA distance for this face is 10-20m.

With a 60 cm face each ring covered is a 3.6m to the distance from the target.
Unmarked distance range for this face is 15-30m.

The distance to width relationship is linear not exponential as I had thought- rubbishing previous attempts at distance comparisons to pats of my button which gave that impression.

By finding the distance your sight window (or other measuring part) covers the entire face and dividing by 10 to get the distance per ring you should be quickly able to suit the method to yourself for each size target.

This method compares well with my practical results of playing about with targets and distances.

It would be interesting to hear anybodies experience of this. It shouldn't be hard to try it out.

Warped Arrow
06-20-2010, 10:57 AM
HUH??? Can you explain that in "back-woods-redneck" speak??

Greysides
06-20-2010, 12:46 PM
Hopefully this will make sense:

The width illustrated is the width of the target face obscured when I hold the riser window up against one side of the target.

The more that is covered, the further away I am.

http://img42.imageshack.us/img42/1962/fieldtargets.jpg

Warped Arrow
06-20-2010, 12:54 PM
That makes it clearer...I guesse my main prob is that I dont shoot alot of actual target faces. I mainly blank bale, or use a coffee can lid as a target.

Here is a pic of my target:

http://i281.photobucket.com/albums/kk231/dragonsheart1004/Archery/10arrows.jpg

http://i281.photobucket.com/albums/kk231/dragonsheart1004/Archery/LHWarf-10yards1.jpg

rusty craine
06-20-2010, 09:53 PM
what if longest shot was 50 meter. each for the 10 meter sections is now given a letter from A to E. find you gap for each section 8 yds into to section. that wold be Section A is shot with amn 8 yd pg. section B is shot with a 18 yd gap. Section C with an 28 yd gap, Section D with a 38 yd gap and section E with a 48 yd gap. so you only know five gaps. indentif y what section you think your target is in and shoot it with that section assigned gap..

just pushing the pencile a bit I don't think you would miss a target. I don't think your scorwe would be too high. but unless I miss calculated you should be on every target if you aim at the kill zone.

Called Defensive gapping.

rusty

Greysides
06-21-2010, 01:33 AM
Rusty, I seen it written, and seen it in practice, that it is better to over estimate than to under-estimate a distance so using 8, rather than 5 as the distance that sets the gap sound fine. Shooting three arrows from the same peg allows you to use the same gap and aim off (point symmetry/central symmetry) for the second and third shots.

The thing about being on the target, apart from at least having a scoring arrow, is that you're not looking for arrows afterwards!


The blue pasted section in the first post is actually a very clever way to use your sight ring..........I finally decoded it last night and I think I can now explain it if asked.
It depends on the width of the sight ring being one hundredth of the distance from your eye to it at full draw. I don't use sights, but my eye to riser window is 71 cm, which is 710 mm, add in a little distance to the sight ring and I'd be close enough to 800 mm, which would make the calculations very easy.

Part of the interpretation problems is the units used:

10mm is 1 cm.
100 cm is 1 m.
1000 mm in 1 m.

The '8' and the '6' refer to the width of the rings, in cm, of a field target- either an 80 cm or a 60 cm; the half ring is therefore either 4 or 3, respectively.

In the example given in blue, you use the width the sight ring covers on the target in cm, to give you your distance from it in metres.

You need to be aware of the cm width of each ring (10 ring widths across a target, each numbered ring counted twice, ignoring the X) and for the length of your draw to give you that nice 1:100 ratio.

Greysides
06-19-2011, 08:42 AM
I came across this today and thought it may be helpful.


YARDAGE ESTIMATION
By Michael Marlow



Consistent yardage estimation in 3-D archery is perhaps the single most important part of the game, yet the least practiced. Most archers enjoy shooting the bow because of the dynamic feeling of accomplishment when they hit a dot the size of a Quarter at 40 yards. They spend hours honing their form by relentlessly pounding the practice target with hundreds of arrows. But when the time comes for yardage practice they only spend a few minutes because itís not as exciting as shooting at and hitting that dot. To be successful at the 3-D game an archer must sacrifice some of the excitement of shooting and spend as much time or more practicing yardage estimation.

Every archer needs a starting point to judge from. I like starting at 20 yards and counting in five-yard increments along the ground to the target. This works well on flat ground but creates problems in hilly terrain because you see more ground from an elevated shooting position. On ranges that are sloping downhill from the shooter stake it is better to reference your yardage off of trees horizontally along your line of sight. I find one that is close to 20 and start estimating to the next tree from there.

The easiest way to find a starting point is to use a distance that is already familiar to you. This can be the length of your house or the distance from your parking place to the door of your house. For example, if your house is 54 feet long you know that is 18 yards. When you are at the stake visualize where your house would end if you were standing at the opposite end. This gives you a point to start from that is already fixed into your psyche and you didnít even know it. Another way of ingraining a starting point is to exclusively shoot at a target at a known distance. Set a target at 25 or 30 yards and practice only from that distance. After a while you will be able to picture where your practice target would be compared to where the tournament target is.

After you find your starting spot find a way that is comfortable to estimate the remaining distance. Use five or ten yard increments from where your starting point is to the target or count back from the target to where your beginning point is.
Many shooters use the halfway method. They find the point that is halfway between you and the target, reference it to the known distance you already know and then double it. An easy way to find the midpoint is to spread your feet apart the same distance as the targetís feet are spaced. Then visualize a line from your right foot to the targets left foot and a line from your left foot to the targets right foot. Where the lines intersect should be the halfway point between you and the target. If you use this method try to get within a half yard with your estimate so that when you double it you donít double a mistake in your estimate.

Probably the best, and most expensive, way to learn how to learn to judge yardage is to use ďhead yardage.Ē This is simply memorizing the targets at different distances. Since this method takes terrain out of the equation it is probably the most consistent way to estimate. This is why it is an expensive way to learn since you need to own all the targets that you will shoot or have access to them. An inexpensive way to get the full benefit of this technique is to cut life-sized replicas from cardboard and set them at known distances. Use distances you normally see in a tournament.

The methods listed above are primary ways to estimate yardage. Donít forget to use other tools that help in your judging. Learn the distances you can clearly see the twelve, ten and eight rings. Use this to estimate the farthest possible distance the target can be from you. If you can clearly see the twelve at 15 yards and the ten at 22 yards and the eight at 30 yards then you can reasonably estimate a range that the target falls between. An example would be a target set at 25 yards you would be able to see the eight ring clearly but not the ten. So you would know the target is between 22 and 30 yards. You will need to practice this in varying shades of light. The brighter it is the better you can see the scoring rings.

Know yourself and how you judge; what I mean is know how you judge in the open in relationship to thick tight ranges. In the open I tend to judge three yards short. In a tunnel situation I will judge two yards long. If the target is partially hidden behind a tree I will judge two yards long. Learn your tendencies and compensate for them on the range.

Use what you have to judge with. A few years ago I was shooting the Second Leg of the IBO Southern Triple Crown and was confronted with a wolf target at 45 yards. The target was set over a rolling hill, which obstructed about half the ground to the target. I could only see the wolf from the belly up. The trail was cut through open pines and had a generous amount of sagebrush growing underneath which worked to my advantage. When the trail was cut there was a perfect wall of grass on both sides. Since I couldnít see the ground I used the wall of grass to count my yardage on and hung a ten. I have also used my chair to get a better view of the ground in the same situation. By standing on the seat you can gain another 15 inches in height.

Take note of the light. If the Sun is behind you and shining on the target the target will appear closer because you see more detail. If the Sun is behind the target you will find the opposite to be true since the part facing you will be in the shade.

Most importantly listen to your subconscious. If that little voice keeps telling you something is wrong with your number, take a little extra time and maybe use a different style of estimating to check your number. Use some of the checks described above and nail that ten ring.

Mike Marlow
Ultimate Archery Pro Shop

aroadik
06-19-2011, 03:09 PM
1 year between posts on this thread ! You are keen :lol:

Greysides
06-20-2011, 06:15 AM
It's a bit of a hobby-horse Pete......................but it's interesting how you can pick up a good pointer where you least expect it................

aroadik
06-20-2011, 03:03 PM
This time I am able to open image !