open TELEMAC-MASCARET The mathematically superior suite of solvers

Hello I am trying to convert the coordinates of Telemac2D results files but I am experiencing some difficulties. My model mesh is built in WGS84 coordinates, which is converted to Telemac mercator corrdinates in the CORRXY subroutine using the following code

DO I = 1 , N
X(I) = RADIUS*(X(I)-LON0)*DTR
Y(I) = RADIUS*( LOG(TAN(Y(I)*0.5D0*DTR+PI*0.25D0))
& -LOG(TAN(LAT0 *0.5D0*DTR+PI*0.25D0)))
ENDDO

I am then post processing the reults files to convert the Telemac mercator coordinates back to WGS84 using the following code which should just be the inverse of what was done previously

R=6371000
pi=3.14259
DTR=pi/180
RTD=180/pi
lon0=0
lat0=50

term2=R*log(tan(radians(lat0/2)+(pi/4)))

def x2lon(x):
lamda=lon0+degrees(x/R)
return lamda

def y2lat(y):
phi=(2*(arctan(exp((y+term2)/R))))-(pi/2)
phi=degrees(phi)
return phi

lono=x2lon(x)
lato=y2lat(y)

However this does not give a good coordinate conversion. I have tried changing the offset values (lon0 and lat0) and this does improve results however there is still a significant error. Has anyone had any experience with this and could you advise me where I might be going wrong?

Thanks

Olly

I am now trying to convert my WGS84 grid into UTM coordinates in the CORRXY subroutine. However I am experiencing some difficulties. I am printing the converted coordinates to a text file to check the calculation and they are of the same order of magnitude but not quite right. I also get the following error

*************************************
* END OF MEMORY ORGANIZATION: *
*************************************

INBIEF (BIEF): NOT A VECTOR MACHINE (ACCORDING TO YOUR DATA)
GEOELT: ELEMENT 100482 : NEGATIVE DETERMINANT

Has anyone done something similar to this before and could advise me as to where I am going wrong?

Thanks

Olly

Hello,

Before looking further, it seems that your value of PI is not correct : 3.14259 ?? Is it not 3.1415926535897932384626433... ???

JMH

Hello, yes so it is. I have corrected that but I still can not seem to convert from Telemac Mercator to WGS84 with any accuracy. I have now debugged my code for converting to UTM which appears to work reasonably well. I will continue to try to convert to WGS84, if you could offer any advice it would be very much appreicated. Thanks for your time.

Olly