## C#
Aircraft Instrument Control

1

The aim of this
**C#** project
is to purpose six aircraft cockpit
**instruments**
usable in forms as any other
**C# controls**
and to define a generic
**instrument** class in order to
design any kind of dashboard
**instruments**.

## 2

The
**controls** are
built with bitmaps which are rotated, translated
or scaled before to be displayed. The basic
methods for rotate, translate and scale images
are defined in the mother class. Each control
then uses its dedicated parameters (related to a
physical signification) in order to manipulates
the images.

##
Aircraft Instruments

- Air speed
indicator: airspeed (kts)
- Attitude
Indicator: pitch (deg), roll (deg)
- Altimeter:
altitude (ft)
- Turn Coordinator:
turn rate (deg/min)
- Vertical speed
indicator: vertical speed (ft/min)
- Heading indicator:
heading (deg)

## 3

This section explains
in detail the implementation of the basic
functions defined in the ```
Instrument
Control
```

class.

### Rotate Image

#### Implementation

The rotation of the
image is divided in two main parts:

First, the rotation of the ```
PaintEventArgs
```

coordinate system
around the upper left corner of the drawing
area.

Second, the drawing of
the image corrected by translation offset in
order to display the image as if it has turned
around a user defined point.

Let’s see step by step:

**Step 0**:
Initial situation.

**Step 1**:
Rotate the ```
PaintEventArgs
```

coordinate system around
the left upper corner of the paint area.

Corresponding code
sample:

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Code
pe.Graphics.RotateTransform((float)(alpha * 180 / Math.PI));

**Step 2**:
Draw the image and apply the translation
correction.

Corresponding code
sample:

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Code
pe.Graphics.DrawImage(img, (ptImg.X + deltaX) * scaleFactor, (ptImg.Y + deltaY) *
scaleFactor, img.Width * scaleFactor, img.Height * scaleFactor);

**Step 3**
(Final step): Put the ```
PainEventArgs
```

coordinate system
as found.

Corresponding code
sample:

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Code
pe.Graphics.RotateTransform((float)(-alpha * 180 / Math.PI));

The key point in those
operations is the calculation of the translation
correction coefficients.

The next figure
explains the geometrics considerations:

G_{0} is the
user defined rotation center

G_{1} is the G_{0} position
after the step 1.

The aim of this section
is to identify the G_{1}G_{0}
translation and apply the corresponding offset
in order to draw the rotation point as if it has
not moved.

Then we work with the
geometrics definitions:

As a result, the offset
coefficients are:

The corresponding code
sample is as follows:

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Code
deltaX = (float)(d * (Math.Cos(alpha - beta) - Math.Cos(alpha)*
Math.Cos(alpha + beta) - Math.Sin(alpha) * Math.Sin(alpha+ beta)));
deltaY = (float)(d * (Math.Sin(beta - alpha) + Math.Sin(alpha)*
Math.Cos(alpha + beta) - Math.Cos(alpha) * Math.Sin(alpha + beta)));

#### Parameters

- "
`pe`

":
The paint area event where the image will be
displayed
- "
`img`

":
The image to display
- "
`alpha`

":
The angle of rotation in radian
- "
`ptImg`

":
The location of the left upper corner of the
image to display in the paint area in
nominal situation
- "
`ptRot`

":
The location of the rotation point in the
paint area
- "
`scaleFactor`

":
Multiplication factor on the display image

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