translation help?

[Bell, Kevin]

I’m translating a function from the mystery language below to python, but I don’t know what I’m doing…  should this get me the same results?  I don’t understand the do/while stuff in the first snippet.

MYSTERY CODE:

        // Substitute the estimate into the iterative calculation that

        // converges on the correct Latitude value.

        var part1 = (1 - (Ec * Math.sin(Lat0))) / (1 + (Ec * Math.sin(Lat0)));

        var LatR = Pi2 - (2 * Math.atan(t * Math.pow(part1,(Ec/2))));

        do {

               Lat0 = LatR;

               part1 = (1 - (Ec * Math.sin(Lat0))) / (1 + (Ec * Math.sin(Lat0)));

               //LatR = Pi2 - (2 * Math.atan2((t * (part1**(Ec/2))),1));

               LatR = Pi2 - (2 * Math.atan(t * Math.pow(part1,(Ec/2))));

        } while (Math.abs(LatR - Lat0) > 0.000000002);

MY PYTHON ATTEMPT:

      part1 = (1 - (Ec * math.sin(Lat0))) / (1 + (Ec * math.sin(Lat0)))

        LatR = Pi2 - (2 * math.atan(t * math.pow(part1,(Ec/2))))

        while (abs(LatR - Lat0) > 0.000000002):

               Lat0 = LatR

               part1 = (1 - (Ec * math.sin(Lat0))) / (1 + (Ec * math.sin(Lat0)))

               LatR = Pi2 - (2 * math.atan(t * math.pow(part1,(Ec/2))))

 

 

Kevin Bell

GIS Specialist

Salt Lake City Transportation Division

349 South 200 East, Suite 450

P.O. Box 145502

Salt Lake City, UT 84114-5502

801-535-7131

 

[Jason Edwards]

Your mystery language looks like JavaScript to me...

[Dennis Muhlestein]

On Jun 23, 10:20 am, "Bell, Kevin" <kevin.b...@slcgov.com> wrote:
> I'm translating a function from the mystery language below to python,

> but I don't know what I'm doing... should this get me the same results?

> I don't understand the do/while stuff in the first snippet.
>
> MYSTERY CODE:
>
> // Substitute the estimate into the iterative calculation that
> // converges on the correct Latitude value.
> var part1 = (1 - (Ec * Math.sin(Lat0))) / (1 + (Ec *
> Math.sin(Lat0)));
> var LatR = Pi2 - (2 * Math.atan(t * Math.pow(part1,(Ec/2))));
> do {
> Lat0 = LatR;
> part1 = (1 - (Ec * Math.sin(Lat0))) / (1 + (Ec *
> Math.sin(Lat0)));
> //LatR = Pi2 - (2 * Math.atan2((t * (part1**(Ec/2))),1));
> LatR = Pi2 - (2 * Math.atan(t * Math.pow(part1,(Ec/2))));
> } while (Math.abs(LatR - Lat0) > 0.000000002);
>
> MY PYTHON ATTEMPT:
> part1 = (1 - (Ec * math.sin(Lat0))) / (1 + (Ec * math.sin(Lat0)))
> LatR = Pi2 - (2 * math.atan(t * math.pow(part1,(Ec/2))))
> while (abs(LatR - Lat0) > 0.000000002):
> Lat0 = LatR
> part1 = (1 - (Ec * math.sin(Lat0))) / (1 + (Ec *
> math.sin(Lat0)))
> LatR = Pi2 - (2 * math.atan(t * math.pow(part1,(Ec/2))))
>

In Python, there is no do..while construct. The difference is that a
do while loop will always execute at least once since the while
condition is evaluated after the 1st execution. In a while loop, if
the condition is satisfied, the loop may never execute.

While there is probably a better solution, you can simulate the do/
while behavior like this:

while True:
# statements
if condition:
break

-Dennis