Draw the other half
A half-vase is displayed on screen. Draw the missing half and the feedback reflects your outline across the center line onto the given half. You can see the mismatch from the rim to the foot.
The missing half of a half drawn vase must be completed from the rim down to the foot of the vase.
The technique
Draw the other half of a symmetrical object
4 steps
- 01
Mark the heights first
Tick for the three heights at the narrowest part of the neck, the widest part of the belly and the base of the vase.
- 02
Carry two widths across
Compare the distance from the axis to the given outline at the neck and belly. Place light ticks the same distance on your side. Use those two widths as guides while you draw.
- 03
Draw through the marks
Draw from the rim toward the foot, passing through your planned widths. Try a flowing contour, using a few connected strokes if that is more comfortable. Keep the joins readable.
- 04
Check back before you finish
As you reach the belly and foot, compare their heights and widths with the given half. Adjust a mismatch if needed, keeping one clear outline rather than several competing contours.
How it works
What it can name
The faults, drawn
These percentages can mean nothing by themselves. Instead, each problem has its own fix. The examples below are all real strokes that I generated with the same code that I used to test the engine.
Narrow half
The added half is narrower overall than the reference. Compare distances from the dashed axis at matching heights.
Wide half
The added half is wider overall than the reference. Compare distances from the dashed axis at matching heights.
Right widths, wrong heights
The neck and belly sit too high in this example. Matching their heights as well as their widths brings the two halves closer together.
Comes apart on the way down
The outline's width error grows toward the foot. Compare the given half at the neck, belly and base as you draw.
Does not close
The two halves need to meet at the rim and base. Aim for the visible endpoints while also matching widths along the sides.
How the number is made
What the score actually measures
Width match
mean |your half-width − given half-width| ÷ widest half-width32% of the scoreYour half is compared with the given one at 96 heights. These samples build the width-error measurement and show where the outlines differ; they do not inspect every possible point on the line.
Lean
mean SIGNED difference ÷ widest half-width22% of the scoreThe direction of your misses. If your half is consistently narrower or wider, the signed average shows which way it tends to differ. It describes this attempt, not what everyone’s eye normally does.
Feature height
the vertical slide that best fits your profile onto the given one14% of the scoreWhether your neck and belly have similar widths to the reference but sit too high or too low. The engine tries shifting the profile vertically to see how much of the mismatch that explains. A better fit suggests a placement issue; it need not remove every error.
Steadiness
slope of the error from rim to foot13% of the scoreIs your error growing or staying the same? A growing error is a different fault than a constant error and so needs a different correction.
Your side of the line
deepest ink past the centre line, as a share of the widest half-width10% of the scoreWhether the outline stays on the missing half’s side of the center line. The axis is fixed, so crossing it can be measured directly. Keep the side contour outside that line; the connections at the rim and foot are checked separately.
Closing
distance from each end to the given half9% of the scoreHow the outline connects at the rim and foot. Bring your new half to those joining areas so the vase reads as one silhouette. The engine measures the gaps; tiny differences do not require an immaculate join.
The score gives most weight to matching the widths and to any consistent narrow-or-wide tendency. Placement, growing drift and the joins add context. Those measures help you choose a correction without assuming you cannot see the problem yourself. Every threshold, and the evidence behind it.
When the second half comes out narrow
Matching a width across the center line can be harder than it looks. If your half comes out narrow, compare the neck and belly distances directly. That gives you two places to check without assuming your eye always underestimates a gap.
The same comparison can help with other forms meant to be symmetrical, such as a front-facing vase or building. Decide which parts should match before comparing them. A turned face or deliberately uneven character can have different widths for good reasons.
Before drawing the outline, carry the neck and belly widths across the axis with two light guide ticks. You now have positions to draw through, rather than having to judge every width while the pen is moving.
Right widths, wrong heights
Another possible mismatch is height: the neck and belly can be about the right width but sit too high or too low. The vertical-shift measurement checks for this pattern. If moving the profile improves the fit, compare those landmark heights before redrawing.
Following an outline and keeping its landmarks at matching heights are different parts of this task. You might draw a smooth contour but place its belly too high. The width and placement feedback help separate those visible problems, without diagnosing your overall ability.
If the feedback points to misplaced neck or belly heights, mark those levels and the foot before your next outline. A low score for a different reason may need a different adjustment.
What the fold shows you
When you finish, the feedback reflects your half across the center line onto the given one and highlights the mismatch. The overlay shows where the widths differ alongside the numerical result. You do not have to fold paper or fill in the gap yourself.
It is similar to extending box edges to inspect how they converge: an overlay makes a relationship easier to see. The numbers and the picture give you two ways to inspect the same attempt, subject to the recorded line and the measurement’s limits.
When you have got it
As a practice target, aim for widths within about two percent and no consistent narrow-or-wide tendency. Use the neck and belly checks to plan it. This is a target to work toward, not a claim that you have already drawn it or a limit on how often you may check.
Questions
Why is my half always narrower than the given one?
Your half may have ended up narrower while you judged widths across the gap. Check the neck and belly distances from the axis and place matching ticks before the next outline. See whether that helps your own attempt; narrowness is not inevitable or evidence of a particular memory habit.
Does the given half stay visible?
Yes, the whole time. What you’re trying to measure is the ability to match a seen width, not a memory test. Hiding the reference would measure something entirely different.
Which side do I draw on?
There’s no setting involved for the blank one. The drill knows which side of the page your ink is on.
Do I need a tablet for this?
No tablet is required. The measurements run in your browser with mouse, pen or touch input. They are scaled to the drawing’s dimensions, but different devices can still affect how easily you place and control the line.
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