/**
* * Calculate the glideslope given our current position/altitude and the position/elevation of
* the target airport
*
* @param gpsParams where we are
* @param dest what our destination is
*/
public void calcGlideSlope(GpsParams gpsParams, Destination dest) {
// Show no vertical offset by default
mDspOffset = 0;
mBackColor = mColorOn;
// If either of these objects are null, there is nothing
// we can do
if (dest == null || gpsParams == null) {
mShow = false;
return;
}
// Fetch the elevation of our destination. If we can't find it
// then we don't want to display any vertical information
double destElev = dest.getElevation();
if (destElev == -200) {
mShow = false;
return;
}
// Calculate our relative AGL compared to destination. If we are
// lower then no display info
double relativeAGL = gpsParams.getAltitude() - destElev;
// Convert the destination distance to feet.
double destDist = dest.getDistance();
double destInFeet = mConvertToFt * destDist;
// Figure out our glide slope now based on our AGL height and distance
mGlideSlope = Math.toDegrees(Math.atan(relativeAGL / destInFeet));
// Set the color of the glide slope background. According to the AIM,
//
if (mGlideSlope < (3 - BAR_DEGREES)) {
mBackColor = mColorLow;
} else if (mGlideSlope > (3 + BAR_DEGREES)) {
mBackColor = mColorHigh;
}
// Calculate the vertical display offset of the indicator
// Anything greater/equal to 3.7 pegs at the top
// Anything less/equal to 2.3 pegs at the bottom
// all others scale in between based upon instrument height
double fullDeflection = mInstHeight / 2 - mBarHeight * 1.5;
if (mGlideSlope >= 3.7) {
mDspOffset = -(int) fullDeflection;
} else if (mGlideSlope <= 2.3) {
mDspOffset = (int) fullDeflection;
} else {
mDspOffset =
-(int) ((((mGlideSlope - 3) / BAR_DEGREES)) * (fullDeflection / ((mBarCount - 1) / 2)));
}
mShow = true;
}
/**
* * Draw the instrument on the canvas given the current screen size This is called during the
* screen refresh/repaint - be quick about it; no "new" calls.
*
* @param canvas What to draw upon
* @param screenX Total width of the display canvas
* @param screenY Total height of the display canvas
* @param dest The target destination
*/
public void drawVNAV(Canvas canvas, float screenX, float screenY, Destination dest) {
// If we have no destination set, then do not draw anything
if (dest == null || (!mShow)) {
mShow = false;
return;
}
// If we are more than 30 miles from our target, then do not
// draw anything
double destDist = dest.getDistance();
if (destDist > APPROACH_DISTANCE) {
mShow = false;
return;
}
// Calculate the top position of the instrument
mInstTop = (screenY - mInstHeight) / 2;
// Now the left side
mInstLeft = screenX - mInstWidth; // Right side of display
// Draw the background
mVNAVPaint.setColor(mBackColor); // Color
mVNAVPaint.setAlpha(0x5F); // Make it see-thru
mVNAVPaint.setStrokeWidth(mInstWidth); // How tall the inst is
mVNAVPaint.setStyle(Paint.Style.STROKE); // Type of brush
// Draw the background of the instrument. This is a vertical swipe top to bottom.
canvas.drawLine(mInstLeft, mInstTop, mInstLeft, mInstTop + mInstHeight, mVNAVPaint);
// Draw all of the horizontal bars
mVNAVPaint.setColor(Color.WHITE); // white
mVNAVPaint.setStrokeWidth(mBarHeight); // height of each bar
for (int idx = 0; idx < mBarCount; idx++) {
float extend = (idx == (int) (mBarCount / 2)) ? mInstWidth / 3 : 0;
float barTop = mInstTop + mBarHeight * (float) 1.5 + idx * (mBarHeight + mBarSpace);
canvas.drawLine(
mInstLeft + mBarHeight - mInstWidth / 2,
barTop,
mInstLeft + mBarHeight + mBarWidth - mInstWidth / 2 + extend,
barTop,
mVNAVPaint);
}
// Now draw the needle indicator at the vertical center adjusted by the offset
drawIndicator(canvas, screenY / 2 - mDspOffset);
}