# Tidal harmonics and ellipses

## Complex Field
Most tidal harmonics are stored in amplitude and phase lag (FES, SYMPHONIE, MIOST-IT, etc.) but some of them are also stored in real and imaginary part (HRET).

### Setup for amplitude/phase complex variables:
1. Primary menu → [file name] → [amplitude variable], then Secondary menu → p → interp 
2. Primary menu → [file name] → [phase variable], then Secondary menu → p → phase

![Tidal Harmonics](../../_static/tidal_menu.jpg)

### Setup for real/imaginary complex variables:
1. Primary menu → formulaAndIso → p = re + 1j*im, 
j refers to the imaginary unit ( j² = -1 ).
2. Primary menu → [file name] → [real variable], 
then Secondary menu → re → interp
3. Primary menu → [file name] → [imaginary variable], 
then Secondary menu → im → interp

### Isophases:
1. Primary menu → formulaAndIso → pG = -arg(p)*r2d 
2. Select pG
3. View window → display → Select formula variable settings... [F12]
4. isovalues → -180 *30 180 → Apply

## Tidal ellipses: 
By setting complex velocities on u and v the arrows will become ellipses and the colored field will refers to the amplitude of the velocity field.

Primary menu → [file name] :
1. [U amplitude variable], then Secondary menu → u → interp 
2. [U phase variable], then Secondary menu → u → phase
1. [V amplitude variable], then Secondary menu → v → interp 
2. [V phase variable], then Secondary menu → v → phase

*TIPS: When manipulated heavy files, check the "freeze" box in the View window before setting all the variable, then uncheck it to apply all the changes at once*

![Tidal Ellipses](../../_static/tidal_ellipses.jpg)