My first post here. I'm designing a map at 500.000 for Italy and with EPSG 3035 or 3034 (Lambert Conical Conformal) I'm still deciding... anyway... In my map I've several points whose symbol is a sort of "rose of winds" and I need they will remain aligned with the Grid North. How could I do that? I think I'd have to calculate the angle between the Grid North and True North so I could put its value in a column that Qgis can read as an angle of rotation.

I tried with the formula

                        γ = arctan [tan (λ - λ0) × sin φ]

but I think there's something wrong coause the symbol doesn't align with the grid.

  • tan and sin most probably expect input in radians, not degree. And the result will be in radians too. – AndreJ Aug 10 '15 at 9:36
  • Do you confirm that formula is the right one for those projections? – Forna Aug 10 '15 at 9:46
  • I have not tested it. – AndreJ Aug 10 '15 at 10:42
  • ok... I searched the web and found this discussion: atpforum.eu/forum/technical-subjects/-061-general-navigation/… – Forna Aug 10 '15 at 16:35

ok... I searched the web and found this discussion:


so I've written (all in decimal degree) this: 360 - [(λ - λ0) x sinφ0)]

λ = point of interest's longitude λ0 = 10 (longitude of EPSG 3034 origin) φ0 = 52 (latitude of EPSG 3034 origin)

Now I've a more consistent rotation for symbols and they appear parallel to grid.

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