Complete Procedure for Geographic Centroid Calculation in MIT App Inventor
1. Set Up Your Project
•	Create a new project in MIT App Inventor, then set up the User Interface with:
o	Text Inputs for the user to enter latitude and longitude values (two inputs per point).
o	A Button labeled "Calculate Centroid" to trigger the centroid calculation.
o	Two Labels to display the results: one for "Centroid Latitude" and the other for "Centroid Longitude".
2. Initialize Global Variables
In the Blocks section:
•	Initialize the following global variables:
o	global xSum: 0
o	global ySum: 0
o	global zSum: 0
o	global n: 0 (to count the number of points)
o	global centroidLatitude: 0
o	global centroidLongitude: 0
3. Create a Procedure for Fractional Calculation (frac)
1.	Create a New Procedure:
o	Drag out a Procedure block, name it frac, and add an input named value.
2.	Inside the Procedure:
o	Initialize a local variable integerPart:
	Use the int block: integerPart = int(value)
o	Calculate the fractional part:
	Set fracValue to value - integerPart.
o	Use a return block to return fracValue.
4. Main Calculation Logic
When the "Calculate Centroid" Button is Clicked:
1.	Reset Variables: 
o	Set global xSum to 0.
o	Set global ySum to 0.
o	Set global zSum to 0.
o	Set global n to 0.
2.	Loop Through Each Latitude/Longitude Point:
o	Use a for each item in list block, where the list consists of latitude and longitude pairs.
o	For each pair:
	Convert Latitude and Longitude to Radians:
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latRadians = latitude * (π / 180)
lonRadians = longitude * (π / 180)
	Calculate Cartesian Coordinates:
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x = cos(latRadians) * cos(lonRadians)
y = cos(latRadians) * sin(lonRadians)
z = sin(latRadians)
	Accumulate Sums:
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global xSum = global xSum + x
global ySum = global ySum + y
global zSum = global zSum + z
global n = global n + 1
5. Calculate Averages
After processing all points, calculate the averages and hypotenuse:
1.	Calculate Averages:
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xAvg = global xSum / global n
yAvg = global ySum / global n
zAvg = global zSum / global n
2.	Calculate the Hypotenuse:
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hyp = sqrt(xAvg * xAvg + yAvg * yAvg)
6. Calculate Longitude and Latitude
Using conditional blocks to calculate the centroid coordinates:
1.	Calculate Longitude:
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if xAvg > 0:
    global centroidLongitude = atan(yAvg / xAvg)
else if xAvg < 0:
    global centroidLongitude = atan(yAvg / xAvg) + 180
else if xAvg == 0:
    if yAvg < 0:
        global centroidLongitude = 270
    else
        global centroidLongitude = 90
2.	Calculate Latitude:
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global centroidLatitude = atan(zAvg / hyp)
7. Convert Radians to Degrees
Convert the results back to degrees:
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global centroidLatitude = global centroidLatitude * (180 / π)
global centroidLongitude = global centroidLongitude * (180 / π)
8. Display Results
Finally, use the set Label.Text blocks to display the centroid latitude and longitude:
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LabelForLatitude.Text = "Centroid Latitude: " + global centroidLatitude
LabelForLongitude.Text = "Centroid Longitude: " + global centroidLongitude