! File name: oblimap_projection_module.f90 ! ! Copyright (C) 2020 Thomas Reerink & Michael Kliphuis. ! ! This file is distributed under the terms of the ! GNU General Public License. ! ! This file is part of OBLIMAP 2.2 ! ! See Reerink et al. (2010,2016) for OBLIMAP's scientific documentation: ! https://www.geosci-model-dev.net/3/13/2010/ ! https://www.geosci-model-dev.net/9/4111/2016/ ! ! The OBLIMAP User Guide (Reerink, 2016) can be found at: ! https://github.com/oblimap/oblimap/blob/master/documentation/ ! ! The OBLIMAP code can be downloaded by: ! svn checkout https://svn.science.uu.nl/repos/project.oblimap ! or from OBLIMAP's Github by: ! git clone https://github.com/oblimap/oblimap ! ! OBLIMAP is free software: you can redistribute it and/or modify ! it under the terms of the GNU General Public License as published by ! the Free Software Foundation, either version 3 of the License, or ! (at your option) any later version. ! ! OBLIMAP is distributed in the hope that it will be useful, ! but WITHOUT ANY WARRANTY; without even the implied warranty of ! MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the ! GNU General Public License for more details. ! ! You should have received a copy of the GNU General Public License ! along with OBLIMAP. If not, see https://www.gnu.org/licenses/ ! ! ! OBLIMAP is maintained by: ! ! Thomas Reerink ! Institute for Marine and Atmospheric Research Utrecht (IMAU) ! Utrecht University ! Princetonplein 5 ! 3584 CC Utrecht ! The Netherlands ! ! email: tjreerink@gmail.com ! MODULE oblimap_projection_module CONTAINS SUBROUTINE oblique_sg_projection(lambda, phi, x_IM_P_prime, y_IM_P_prime, k_P) ! This subroutine projects with an oblique stereographic projection the longitude-latitude ! coordinates which coincide with the GCM grid points to the rectangular IM coordinate ! system, with coordinates (x,y). ! ! For more information about M, C%alpha_stereographic, the center of projection and the used ! projection method see: ! Reerink et al. (2010), Mapping technique of climate fields between GCM's and ice models, GMD USE oblimap_configuration_module, ONLY: dp, C IMPLICIT NONE ! Input variables: REAL(dp), INTENT(IN) :: lambda ! in degrees REAL(dp), INTENT(IN) :: phi ! in degrees ! Output variables: REAL(dp), INTENT(OUT) :: x_IM_P_prime ! in meter REAL(dp), INTENT(OUT) :: y_IM_P_prime ! in meter REAL(dp), INTENT(OUT), OPTIONAL :: k_P ! Length scale factor [-], k in Snyder (1987) ! Local variables: REAL(dp) :: phi_P ! in radians REAL(dp) :: lambda_P ! in radians REAL(dp) :: t_P_prime ! For North and South Pole: C%lambda_M = 0._dp, to generate the correct IM coordinate ! system, see equation (2.3) or equation (A.53) in Reerink et al. (2010). ! Convert longitude-latitude coordinates to radians: phi_P = C%degrees_to_radians * phi lambda_P = C%degrees_to_radians * lambda ! See equation (2.6) or equation (A.56) in Reerink et al. (2010): t_P_prime = (1._dp + COS(C%alpha_stereographic)) / (1._dp + COS(phi_P) * COS(C%phi_M) * COS(lambda_P - C%lambda_M) + SIN(phi_P) * SIN(C%phi_M)) ! See equations (2.4-2.5) or equations (A.54-A.55) in Reerink et al. (2010): x_IM_P_prime = C%earth_radius * (COS(phi_P) * SIN(lambda_P - C%lambda_M)) * t_P_prime y_IM_P_prime = C%earth_radius * (SIN(phi_P) * COS(C%phi_M) - (COS(phi_P) * SIN(C%phi_M)) * COS(lambda_P - C%lambda_M)) * t_P_prime ! See equation (21-4) on page 157 in Snyder (1987): IF(PRESENT(k_P)) k_P = (1._dp + COS(C%alpha_stereographic)) / (1._dp + SIN(C%phi_M) * SIN(phi_P) + COS(C%phi_M) * COS(phi_P) * COS(lambda_P - C%lambda_M)) END SUBROUTINE oblique_sg_projection SUBROUTINE inverse_oblique_sg_projection(x_IM_P_prime, y_IM_P_prime, lambda_P, phi_P) ! This subroutine projects with an inverse oblique stereographic projection the ! (x,y) coordinates which coincide with the IM grid points to the longitude-latitude ! coordinate system, with coordinates (lambda, phi) in degrees. ! ! For more information about M, C%alpha_stereographic, the center of projection and the used ! projection method see: ! Reerink et al. (2010), Mapping technique of climate fields between GCM's and ice models, GMD USE oblimap_configuration_module, ONLY: dp, C IMPLICIT NONE ! Input variables: REAL(dp), INTENT(IN) :: x_IM_P_prime ! in meter REAL(dp), INTENT(IN) :: y_IM_P_prime ! in meter ! Output variables: REAL(dp), INTENT(OUT) :: lambda_P ! in degrees REAL(dp), INTENT(OUT) :: phi_P ! in degrees ! Local variables: REAL(dp) :: x_3D_P_prime ! in meter REAL(dp) :: y_3D_P_prime ! in meter REAL(dp) :: z_3D_P_prime ! in meter REAL(dp) :: a REAL(dp) :: t_P REAL(dp) :: x_3D_P ! in meter REAL(dp) :: y_3D_P ! in meter REAL(dp) :: z_3D_P ! in meter ! See equations (2.14-2.16) or equations (B.21-B.23) in Reerink et al. (2010): x_3D_P_prime = C%earth_radius * COS(C%alpha_stereographic) * COS(C%lambda_M) * COS(C%phi_M) - SIN(C%lambda_M) * x_IM_P_prime - COS(C%lambda_M) * SIN(C%phi_M) * y_IM_P_prime y_3D_P_prime = C%earth_radius * COS(C%alpha_stereographic) * SIN(C%lambda_M) * COS(C%phi_M) + COS(C%lambda_M) * x_IM_P_prime - SIN(C%lambda_M) * SIN(C%phi_M) * y_IM_P_prime z_3D_P_prime = C%earth_radius * COS(C%alpha_stereographic) * SIN(C%phi_M) + COS(C%phi_M) * y_IM_P_prime ! See equation (2.13) or equation (B.20) in Reerink et al. (2010): a = COS(C%lambda_M) * COS(C%phi_M) * x_3D_P_prime + SIN(C%lambda_M) * COS(C%phi_M) * y_3D_P_prime + SIN(C%phi_M) * z_3D_P_prime ! See equation (2.12) or equation (B.19) in Reerink et al. (2010): t_P = (2._dp * C%earth_radius**2 + 2._dp * C%earth_radius * a) / (C%earth_radius**2 + 2._dp * C%earth_radius * a + x_3D_P_prime**2 + y_3D_P_prime**2 + z_3D_P_prime**2) ! See equations (2.9-2.11) or equations (B.16-B.18) in Reerink et al. (2010): x_3D_P = C%earth_radius * COS(C%lambda_M) * COS(C%phi_M) * (t_P - 1._dp) + x_3D_P_prime * t_P y_3D_P = C%earth_radius * SIN(C%lambda_M) * COS(C%phi_M) * (t_P - 1._dp) + y_3D_P_prime * t_P z_3D_P = C%earth_radius * SIN(C%phi_M) * (t_P - 1._dp) + z_3D_P_prime * t_P ! See equation (2.7) or equation (B.24) in Reerink et al. (2010): IF(x_3D_P < 0._dp ) THEN lambda_P = 180._dp + C%radians_to_degrees * ATAN(y_3D_P / x_3D_P) ELSE IF(x_3D_P > 0._dp .AND. y_3D_P >= 0._dp) THEN lambda_P = C%radians_to_degrees * ATAN(y_3D_P / x_3D_P) ELSE IF(x_3D_P > 0._dp .AND. y_3D_P < 0._dp) THEN lambda_P = 360._dp + C%radians_to_degrees * ATAN(y_3D_P / x_3D_P) ELSE IF(x_3D_P == 0._dp .AND. y_3D_P > 0._dp) THEN lambda_P = 90._dp ELSE IF(x_3D_P == 0._dp .AND. y_3D_P < 0._dp) THEN lambda_P = 270._dp ELSE IF(x_3D_P == 0._dp .AND. y_3D_P == 0._dp) THEN lambda_P = 0._dp END IF ! See equation (2.8) or equation (B.25) in Reerink et al. (2010): IF(x_3D_P /= 0._dp .OR. y_3D_P /= 0._dp) THEN phi_P = C%radians_to_degrees * ATAN(z_3D_P / sqrt(x_3D_P**2 + y_3D_P**2)) ELSE IF(z_3D_P > 0._dp) THEN phi_P = 90._dp ELSE IF(z_3D_P < 0._dp) THEN phi_P = -90._dp END IF END SUBROUTINE inverse_oblique_sg_projection SUBROUTINE inverse_oblique_sg_projection_snyder(x_IM_P_prime, y_IM_P_prime, lambda_P, phi_P) ! This subroutine projects with Snyder's inverse oblique stereographic projection the ! (x,y) coordinates which coincide with the IM grid points to the longitude-latitude ! coordinate system, with coordinates (lambda, phi) in degrees. ! ! For more information about M, C%alpha_stereographic, the center of projection and the used ! projection method see: ! Reerink et al. (2010), Mapping technique of climate fields between GCM's and ice models, GMD ! and ! Snyder (1987), map projections: A working manual, http://pubs.er.usgs.gov/usgspubs/pp/pp1395 USE oblimap_configuration_module, ONLY: dp, C IMPLICIT NONE ! Input variables: REAL(dp), INTENT(IN) :: x_IM_P_prime ! in meter REAL(dp), INTENT(IN) :: y_IM_P_prime ! in meter ! Output variables: REAL(dp), INTENT(OUT) :: lambda_P ! in degrees REAL(dp), INTENT(OUT) :: phi_P ! in degrees ! Local variables: REAL(dp) :: rho REAL(dp) :: angle_C ! in radians REAL(dp) :: numerator REAL(dp) :: denumerator ! See equation (20-18) on page 159 Snyder (1987): rho = SQRT(x_IM_P_prime**2 + y_IM_P_prime**2) ! See equation (21-15) on page 159 Snyder (1987), because the denumerator is always positive this ATAN doesn't ! need a correction like note 2 on page ix in Snyder (1987): angle_C = 2._dp * ATAN(rho / ((1._dp + COS(C%alpha_stereographic)) * C%earth_radius)) ! See equation (20-14) on page 158 Snyder (1987): phi_P = C%radians_to_degrees * ( ASIN(COS(angle_C) * SIN(C%phi_M) + ((y_IM_P_prime * SIN(angle_C) * COS(C%phi_M)) / rho)) ) ! See equation (20-15) on page 159 Snyder (1987): numerator = x_IM_P_prime * SIN(angle_C) denumerator = rho * COS(C%phi_M) * COS(angle_C) - y_IM_P_prime * SIN(C%phi_M) * SIN(angle_C) lambda_P = C%radians_to_degrees * (C%lambda_M + arctangens_quotient(numerator, denumerator)) ! Our choice is to return lambda in the 0-360 degree range: IF(lambda_P < 0._dp) lambda_P = lambda_P + 360._dp ! In case point P coincides with M (see condition at the first line of page 159 Snyder (1987): IF(rho == 0._dp) THEN lambda_P = C%radians_to_degrees * C%lambda_M phi_P = C%radians_to_degrees * C%phi_M END IF END SUBROUTINE inverse_oblique_sg_projection_snyder SUBROUTINE oblique_laea_projection_snyder(lambda, phi, x_IM_P_prime, y_IM_P_prime) ! This subroutine projects with Snyder's oblique Lambert azimuthal equal-area projection the ! longitude-latitude coordinates which coincide with the GCM grid points to the rectangular IM ! coordinate system, with coordinates (x,y). ! ! For more information about M, C%alpha_stereographic, the center of projection and the used ! projection method see: ! Reerink et al. (2010), Mapping technique of climate fields between GCM's and ice models, GMD ! and ! Snyder (1987), map projections: A working manual, http://pubs.er.usgs.gov/usgspubs/pp/pp1395 USE oblimap_configuration_module, ONLY: dp, C IMPLICIT NONE ! Input variables: REAL(dp), INTENT(IN) :: lambda ! in degrees REAL(dp), INTENT(IN) :: phi ! in degrees ! Output variables: REAL(dp), INTENT(OUT) :: x_IM_P_prime ! in meter REAL(dp), INTENT(OUT) :: y_IM_P_prime ! in meter ! Local variables: REAL(dp) :: phi_P ! in radians REAL(dp) :: lambda_P ! in radians REAL(dp) :: t_P_prime ! For North and South Pole: C%lambda_M = 0._dp, to generate the correct IM coordinate ! system, see equation (2.3) or equation (A.53) in Reerink et al. (2010). ! Convert longitude-latitude coordinates to radians: phi_P = C%degrees_to_radians * phi lambda_P = C%degrees_to_radians * lambda ! See equation (21-4) on page 185 of Snyder (1987): t_P_prime = SQRT(2._dp / (1._dp + COS(phi_P) * COS(C%phi_M) * COS(lambda_P - C%lambda_M) + SIN(phi_P) * SIN(C%phi_M))) ! See equations (2.4-2.5) or equations (A.54-A.55) in Reerink et al. (2010), page 185 of Snyder (1987): x_IM_P_prime = C%earth_radius * (COS(phi_P) * SIN(lambda_P - C%lambda_M)) * t_P_prime y_IM_P_prime = C%earth_radius * (SIN(phi_P) * COS(C%phi_M) - (COS(phi_P) * SIN(C%phi_M)) * COS(lambda_P - C%lambda_M)) * t_P_prime END SUBROUTINE oblique_laea_projection_snyder SUBROUTINE inverse_oblique_laea_projection_snyder(x_IM_P_prime, y_IM_P_prime, lambda_P, phi_P) ! This subroutine projects with Snyder's inverse oblique Lambert azimuthal equal-area projection ! the (x,y) coordinates which coincide with the IM grid points to the longitude-latitude ! coordinate system, with coordinates (lambda, phi) in degrees. ! ! For more information about M, C%alpha_stereographic, the center of projection and the used ! projection method see: ! Reerink et al. (2010), Mapping technique of climate fields between GCM's and ice models, GMD ! and ! Snyder (1987), map projections: A working manual, http://pubs.er.usgs.gov/usgspubs/pp/pp1395 USE oblimap_configuration_module, ONLY: dp, C IMPLICIT NONE ! Input variables: REAL(dp), INTENT(IN) :: x_IM_P_prime ! in meter REAL(dp), INTENT(IN) :: y_IM_P_prime ! in meter ! Output variables: REAL(dp), INTENT(OUT) :: lambda_P ! in degrees REAL(dp), INTENT(OUT) :: phi_P ! in degrees ! Local variables: REAL(dp) :: rho REAL(dp) :: angle_C ! in radians REAL(dp) :: numerator REAL(dp) :: denumerator ! See equation (20-18) on page 187 Snyder (1987): rho = SQRT(x_IM_P_prime**2 + y_IM_P_prime**2) ! See equation (24-16) on page 187 Snyder (1987): angle_C = 2._dp * ASIN(rho / (2._dp * C%earth_radius)) ! See equation (20-14) on page 186 Snyder (1987): phi_P = C%radians_to_degrees * ( ASIN(COS(angle_C) * SIN(C%phi_M) + ((y_IM_P_prime * SIN(angle_C) * COS(C%phi_M)) / rho)) ) ! See equation (20-15) on page 186 Snyder (1987): numerator = x_IM_P_prime * SIN(angle_C) denumerator = rho * COS(C%phi_M) * COS(angle_C) - y_IM_P_prime * SIN(C%phi_M) * SIN(angle_C) lambda_P = C%radians_to_degrees * (C%lambda_M + arctangens_quotient(numerator, denumerator)) ! Our choice is to return lambda in the 0-360 degree range: IF(lambda_P < 0._dp) lambda_P = lambda_P + 360._dp ! In case point P coincides with M (see the condition down equation (20-14) on page 186 Snyder (1987): IF(rho == 0._dp) THEN lambda_P = C%radians_to_degrees * C%lambda_M phi_P = C%radians_to_degrees * C%phi_M END IF END SUBROUTINE inverse_oblique_laea_projection_snyder SUBROUTINE oblique_sg_projection_ellipsoid_snyder(lambda, phi, x_IM_P_prime, y_IM_P_prime, k_P) ! This subroutine projects with Snyder's oblique stereographic projection for the ellipsoid ! the the longitude-latitude coordinates which coincide with the GCM grid points to ! the rectangular IM coordinate system, with coordinates (x,y). ! ! For more information about M, C%alpha_stereographic, the center of projection and the used ! projection method see: ! Reerink et al. (2010), Mapping technique of climate fields between GCM's and ice models, GMD ! and ! Snyder (1987), map projections: A working manual, http://pubs.er.usgs.gov/usgspubs/pp/pp1395 USE oblimap_configuration_module, ONLY: dp, C IMPLICIT NONE ! Input variables: REAL(dp), INTENT(IN) :: lambda ! in degrees REAL(dp), INTENT(IN) :: phi ! in degrees ! Output variables: REAL(dp), INTENT(OUT) :: x_IM_P_prime ! in meter REAL(dp), INTENT(OUT) :: y_IM_P_prime ! in meter REAL(dp), INTENT(OUT), OPTIONAL :: k_P ! Length scale factor [-], k in Snyder (1987) ! Local variables: REAL(dp) :: phi_P ! in radians, phi in Snyder (1987) REAL(dp) :: lambda_P ! in radians, lambda in Snyder (1987) REAL(dp) :: chi_P ! in radians, chi in Snyder (1987) REAL(dp) :: A ! For North and South Pole: C%lambda_M = 0._dp, to generate the correct IM coordinate ! system, see equation (2.3) or equation (A.53) in Reerink et al. (2010). IF(C%polar_projection) THEN ! The polar case is excepted from the oblique formula's, see page 161 Snyder (1987) IF(PRESENT(k_P)) THEN ! Output: x_IM_P_prime, y_IM_P_prime, k_P CALL polar_sg_projection_ellipsoid_snyder(lambda, phi, x_IM_P_prime, y_IM_P_prime, k_P) ELSE ! Output: x_IM_P_prime, y_IM_P_prime CALL polar_sg_projection_ellipsoid_snyder(lambda, phi, x_IM_P_prime, y_IM_P_prime) END IF ELSE ! The oblique case, see page 160 Snyder (1987) ! Convert longitude-latitude coordinates to radians: phi_P = C%degrees_to_radians * phi lambda_P = C%degrees_to_radians * lambda ! See equations (3-1a) and (21-27) on page 160 in Snyder (1987): chi_P = 2._dp * ATAN(SQRT(((1._dp + SIN(phi_P)) / (1._dp - SIN(phi_P))) * & ((1._dp - C%e * SIN(phi_P)) / (1._dp + C%e * SIN(phi_P)))**(C%e))) - 0.5_dp * C%pi A = C%akm / (COS(C%chi_M) * (1._dp + SIN(C%chi_M) * SIN(chi_P) + COS(C%chi_M) * COS(chi_P) * COS(lambda_P - C%lambda_M))) ! See equations (21-24) and (21-25) on page 160 in Snyder (1987): x_IM_P_prime = A * COS(chi_P) * SIN(lambda_P - C%lambda_M) y_IM_P_prime = A * (COS(C%chi_M) * SIN(chi_P) - SIN(C%chi_M) * COS(chi_P) * COS(lambda_P - C%lambda_M)) ! See equation (21-26) on page 160 in Snyder (1987): IF(PRESENT(k_P)) k_P = (A * COS(chi_P)) / (C%a * (COS(phi_P) / SQRT(1.0_dp - (C%e * SIN(phi_P))**2))) END IF END SUBROUTINE oblique_sg_projection_ellipsoid_snyder SUBROUTINE polar_sg_projection_ellipsoid_snyder(lambda, phi, x_IM_P_prime, y_IM_P_prime, k_P) ! This subroutine projects with Snyder's polar stereographic projection for the ellipsoid ! the the longitude-latitude coordinates which coincide with the GCM grid points to ! the rectangular IM coordinate system, with coordinates (x,y). See Snyder (1987) p. 161. ! ! The examples of Snyder (1987) at p. 314-315 with the international ellipsoid are used to ! validate this forward SG projection on the ellipsoid for the polar aspect. ! ! For more information about M, C%alpha_stereographic, the center of projection and the used ! projection method see: ! Reerink et al. (2010), Mapping technique of climate fields between GCM's and ice models, GMD ! and ! Snyder (1987), map projections: A working manual, http://pubs.er.usgs.gov/usgspubs/pp/pp1395 USE oblimap_configuration_module, ONLY: dp, C IMPLICIT NONE ! Input variables: REAL(dp), INTENT(IN) :: lambda ! in degrees REAL(dp), INTENT(IN) :: phi ! in degrees ! Output variables: REAL(dp), INTENT(OUT) :: x_IM_P_prime ! in meter REAL(dp), INTENT(OUT) :: y_IM_P_prime ! in meter REAL(dp), INTENT(OUT), OPTIONAL :: k_P ! Length scale factor [-], k in Snyder (1987) ! Local variables: REAL(dp) :: phi_P ! in radians REAL(dp) :: lambda_P ! in radians REAL(dp) :: phi_C ! in radians, phi_c in Snyder (1987), the standard parallel REAL(dp) :: t_P ! REAL(dp) :: t_C ! REAL(dp) :: m_C ! REAL(dp) :: rho ! REAL(dp) :: pf ! polar factor: -1.0 for SP and +1.0 for NP REAL(dp) :: k0 ! Length scale factor at center M [-] IF(C%phi_M == - 90.0_dp * C%degrees_to_radians) THEN pf = -1.0_dp ! The polar factor for the SP ELSE pf = 1.0_dp ! The polar factor for the NP END IF phi_C = (C%degrees_to_radians * 90.0_dp - C%alpha_stereographic) * pf ! Convert longitude-latitude coordinates to radians: phi_P = C%degrees_to_radians * phi lambda_P = C%degrees_to_radians * lambda IF(C%alpha_stereographic == 0.0_dp) THEN ! This variant is only considered for the case that C%alpha_stereographic = 0, i.e. k0 = 1, for which the else-option does not work). ! The POLAR ASPECT WITH KNOWN k0 case: !t_P = TAN(pi / 4.0_dp - phi_P * pf / 2.0_dp) / ( (1.0_dp - C%e * SIN(phi_P * pf)) / (1.0_dp + C%e * SIN(phi_P * pf)) )**(C%e / 2.0_dp) ! (15-9) on page 161 in Snyder (1987) t_P = ( ((1.0_dp - SIN(phi_P * pf)) / (1.0_dp + SIN(phi_P * pf))) * ((1.0_dp + C%e * SIN(phi_P * pf)) / (1.0_dp - C%e * SIN(phi_P * pf)))**C%e )**0.5_dp ! (15-9a) on page 161 in Snyder (1987) k0 = 0.5_dp * (1.0_dp + COS(C%alpha_stereographic)) ! in fact it will be always 1 because it is only used for C%alpha_stereographic = 0 rho = 2.0_dp * C%a * k0 * t_P / ( (1.0_dp + C%e)**(1.0_dp + C%e) * (1.0_dp - C%e)**(1.0_dp - C%e) )**0.5_dp ! (21-33) on page 161 in Snyder (1987) ELSE ! The POLAR ASPECT WITH KNOWN STANDARD PARALLEL NOT AT POLE case: !t_P = TAN(pi / 4.0_dp - phi_P * pf / 2.0_dp) / ( (1.0_dp - C%e * SIN(phi_P * pf)) / (1.0_dp + C%e * SIN(phi_P * pf)) )**(C%e / 2.0_dp) ! (15-9) on page 161 in Snyder (1987) t_P = ( ((1.0_dp - SIN(phi_P * pf)) / (1.0_dp + SIN(phi_P * pf))) * ((1.0_dp + C%e * SIN(phi_P * pf)) / (1.0_dp - C%e * SIN(phi_P * pf)))**C%e )**0.5_dp ! (15-9a) on page 161 in Snyder (1987) !t_C = TAN(pi / 4.0_dp - phi_C * pf / 2.0_dp) / ( (1.0_dp - C%e * SIN(phi_C * pf)) / (1.0_dp + C%e * SIN(phi_C * pf)) )**(C%e / 2.0_dp) ! (15-9) on page 161 in Snyder (1987) t_C = ( ((1.0_dp - SIN(phi_C * pf)) / (1.0_dp + SIN(phi_C * pf))) * ((1.0_dp + C%e * SIN(phi_C * pf)) / (1.0_dp - C%e * SIN(phi_C * pf)))**C%e )**0.5_dp ! (15-9a) on page 161 in Snyder (1987) m_C = COS(phi_C * pf) / (1.0_dp - C%e**2 * SIN(phi_C * pf)**2)**0.5_dp ! (14-15) on page 160 in Snyder (1987) rho = C%a * m_C * t_P / t_C ! (21-34) on page 161 in Snyder (1987) END IF x_IM_P_prime = rho * SIN(lambda_P * pf - C%lambda_M * pf) * pf ! (21-30) on page 161 in Snyder (1987) y_IM_P_prime = - rho * COS(lambda_P * pf - C%lambda_M * pf) * pf ! (21-31) on page 161 in Snyder (1987) IF(PRESENT(k_P)) k_P = rho / (C%a * (COS(phi_P * pf) / SQRT(1.0_dp - (C%e * SIN(phi_P * pf))**2))) ! (21-32) on page 161 in Snyder (1987) END SUBROUTINE polar_sg_projection_ellipsoid_snyder SUBROUTINE inverse_oblique_sg_projection_ellipsoid_snyder(x_IM_P_prime, y_IM_P_prime, lambda_P, phi_P) ! This subroutine projects with Snyder's inverse oblique stereographic projection for the ellipsoid ! the (x,y) coordinates which coincide with the IM grid points to the longitude-latitude ! coordinate system, with coordinates (lambda, phi) in degrees. ! ! For more information about M, C%alpha_stereographic, the center of projection and the used ! projection method see: ! Reerink et al. (2010), Mapping technique of climate fields between GCM's and ice models, GMD ! and ! Snyder (1987), map projections: A working manual, http://pubs.er.usgs.gov/usgspubs/pp/pp1395 USE oblimap_configuration_module, ONLY: dp, C IMPLICIT NONE ! Input variables: REAL(dp), INTENT(IN) :: x_IM_P_prime ! in meter REAL(dp), INTENT(IN) :: y_IM_P_prime ! in meter ! Output variables: REAL(dp), INTENT(OUT) :: lambda_P ! in degrees REAL(dp), INTENT(OUT) :: phi_P ! in degrees ! Local variables: REAL(dp) :: rho REAL(dp) :: angle_C ! in radians REAL(dp) :: chi_P ! in radians, chi in Snyder (1987) REAL(dp) :: numerator REAL(dp) :: denumerator IF(C%polar_projection) THEN ! The inverse polar case is excepted from the inverse oblique formula's, see page 161 Snyder (1987) ! Output: lambda_P, phi_P CALL inverse_polar_sg_projection_ellipsoid_snyder(x_IM_P_prime, y_IM_P_prime, lambda_P, phi_P) ELSE ! The inverse oblique case, see page 160 Snyder (1987) ! See equation (20-18) on page 162 Snyder (1987): rho = SQRT(x_IM_P_prime**2 + y_IM_P_prime**2) ! See equation (21-38) on page 162 Snyder (1987): angle_C = 2._dp * ATAN(rho * COS(C%chi_M) / C%akm) ! See equations (21-37) on page 161 in Snyder (1987): chi_P = ASIN(COS(angle_C) * SIN(C%chi_M) + y_IM_P_prime * SIN(angle_C) * COS(C%chi_M) / rho) ! See equation (3-5) on page 162 instead of equation (3-4) on page 161 Snyder (1987): phi_P = C%radians_to_degrees * (chi_P + & (C%e**2 / 2._dp + 5._dp * C%e**4 / 24._dp + C%e**6 / 12._dp + 13._dp * C%e**8 / 360._dp) * SIN(2._dp * chi_P) + & ( 7._dp * C%e**4 / 48._dp + 29._dp * C%e**6 / 240._dp + 811._dp * C%e**8 / 11520._dp) * SIN(4._dp * chi_P) + & ( 7._dp * C%e**6 / 120._dp + 81._dp * C%e**8 / 1120._dp) * SIN(6._dp * chi_P) + & ( 4279._dp * C%e**8 / 161280._dp) * SIN(8._dp * chi_P)) ! See equation (21-36) on page 161 Snyder (1987): numerator = x_IM_P_prime * SIN(angle_C) denumerator = rho * COS(C%chi_M) * COS(angle_C) - y_IM_P_prime * SIN(C%chi_M) * SIN(angle_C) lambda_P = C%radians_to_degrees * (C%lambda_M + arctangens_quotient(numerator, denumerator)) ! Our choice is to return lambda in the 0-360 degree range: IF(lambda_P < 0._dp) lambda_P = lambda_P + 360._dp ! In case point P coincides with M (see condition at the first line of page 162 Snyder (1987): IF(rho == 0._dp) THEN lambda_P = C%radians_to_degrees * C%lambda_M phi_P = C%radians_to_degrees * C%phi_M END IF END IF END SUBROUTINE inverse_oblique_sg_projection_ellipsoid_snyder SUBROUTINE inverse_polar_sg_projection_ellipsoid_snyder(x_IM_P_prime, y_IM_P_prime, lambda_P, phi_P) ! This subroutine projects with Snyder's inverse polar stereographic projection for the ellipsoid ! the (x,y) coordinates which coincide with the IM grid points to the longitude-latitude ! coordinate system, with coordinates (lambda, phi) in degrees. See Snyder (1987) p. 162. ! ! The examples of Snyder (1987) at p. 317-318 with the international ellipsoid are used to ! validate this inverse SG projection on the ellipsoid for the polar aspect. ! ! For more information about M, C%alpha_stereographic, the center of projection and the used ! projection method see: ! Reerink et al. (2010), Mapping technique of climate fields between GCM's and ice models, GMD ! and ! Snyder (1987), map projections: A working manual, http://pubs.er.usgs.gov/usgspubs/pp/pp1395 USE oblimap_configuration_module, ONLY: dp, C IMPLICIT NONE ! Input variables: REAL(dp), INTENT(IN) :: x_IM_P_prime ! in meter REAL(dp), INTENT(IN) :: y_IM_P_prime ! in meter ! Output variables: REAL(dp), INTENT(OUT) :: lambda_P ! in degrees, lambda in Snyder (1987) REAL(dp), INTENT(OUT) :: phi_P ! in degrees, phi in Snyder (1987) ! Local variables: REAL(dp) :: chi_P ! in radians, chi in Snyder (1987) REAL(dp) :: phi_C ! in radians, phi_c in Snyder (1987), the standard parallel REAL(dp) :: t_P REAL(dp) :: t_C REAL(dp) :: m_C REAL(dp) :: rho REAL(dp) :: pf ! polar factor: -1.0 for SP and +1.0 for NP REAL(dp) :: k0 IF(C%phi_M == - 90.0_dp * C%degrees_to_radians) THEN pf = -1.0_dp ! The polar factor for the SP ELSE pf = 1.0_dp ! The polar factor for the NP END IF phi_C = (C%degrees_to_radians * 90.0_dp - C%alpha_stereographic) * pf rho = SQRT(x_IM_P_prime**2 + y_IM_P_prime**2) ! (20-18) on page 162 in Snyder (1987) IF(C%alpha_stereographic == 0.0_dp) THEN ! This variant is only considered for the case that C%alpha_stereographic = 0, i.e. k0 = 1, for which the else-option does not work). ! The POLAR ASPECT WITH KNOWN k0 case: k0 = 0.5_dp * (1.0_dp + COS(C%alpha_stereographic)) ! in fact it will be always 1 because it is only used for C%alpha_stereographic = 0 t_P = rho * ( (1.0_dp + C%e)**(1.0_dp + C%e) * (1.0_dp - C%e)**(1.0_dp - C%e) )**0.5_dp / (2.0_dp * C%a * k0) ! (21-39) on page 162 in Snyder (1987) ELSE ! The POLAR ASPECT WITH KNOWN STANDARD PARALLEL NOT AT POLE case: !t_C = TAN(pi / 4.0_dp - phi_C * pf / 2.0_dp) / ( (1.0_dp - C%e * SIN(phi_C * pf)) / (1.0_dp + C%e * SIN(phi_C * pf)) )**(C%e / 2.0_dp) ! (15-9) on page 161 in Snyder (1987) t_C = ( ((1.0_dp - SIN(phi_C * pf)) / (1.0_dp + SIN(phi_C * pf))) * ((1.0_dp + C%e * SIN(phi_C * pf)) / (1.0_dp - C%e * SIN(phi_C * pf)))**C%e )**0.5_dp ! (15-9a) on page 161 in Snyder (1987) m_C = COS(phi_C * pf) / (1.0_dp - C%e**2 * SIN(phi_C * pf)**2)**0.5_dp ! (14-15) on page 160 in Snyder (1987) t_P = rho * t_C / (C%a * m_C) ! (21-40) on page 162 in Snyder (1987) END IF ! Note: Eventually replace ATAN with arctangens_quotient(numerator = rho * t_C, denumerator = C%a * m_C) : chi_P = C%pi / 2.0_dp - 2.0_dp * ATAN(t_P) ! (7-13) on page 162 in Snyder (1987) ! See equation (3-5) on page 162 instead of equation (7-9) on page 162 Snyder (1987): phi_P = C%radians_to_degrees * (chi_P + & (C%e**2 / 2._dp + 5._dp * C%e**4 / 24._dp + C%e**6 / 12._dp + 13._dp * C%e**8 / 360._dp) * SIN(2._dp * chi_P) + & ( 7._dp * C%e**4 / 48._dp + 29._dp * C%e**6 / 240._dp + 811._dp * C%e**8 / 11520._dp) * SIN(4._dp * chi_P) + & ( 7._dp * C%e**6 / 120._dp + 81._dp * C%e**8 / 1120._dp) * SIN(6._dp * chi_P) + & ( 4279._dp * C%e**8 / 161280._dp) * SIN(8._dp * chi_P)) *pf ! (3-5) on page 162 in Snyder (1987) lambda_P = C%radians_to_degrees * (C%lambda_M * pf + arctangens_quotient(x_IM_P_prime * pf, - y_IM_P_prime * pf)) *pf ! (20-16) on page 162 in Snyder (1987) ! Our choice is to return lambda in the 0-360 degree range: IF(lambda_P < 0._dp) lambda_P = lambda_P + 360._dp END SUBROUTINE inverse_polar_sg_projection_ellipsoid_snyder SUBROUTINE oblique_laea_projection_ellipsoid_snyder(lambda, phi, x_IM_P_prime, y_IM_P_prime, k_P) ! This subroutine projects with Snyder's oblique Lambert azimuthal equal-area projection for ! the ellipsoid the longitude-latitude coordinates which coincide with the GCM grid points to ! the rectangular IM coordinate system, with coordinates (x,y). ! ! For more information about M, C%alpha_stereographic, the center of projection and the used ! projection method see: ! Reerink et al. (2010), Mapping technique of climate fields between GCM's and ice models, GMD ! and ! Snyder (1987), map projections: A working manual, http://pubs.er.usgs.gov/usgspubs/pp/pp1395 USE oblimap_configuration_module, ONLY: dp, C IMPLICIT NONE ! Input variables: REAL(dp), INTENT(IN) :: lambda ! in degrees REAL(dp), INTENT(IN) :: phi ! in degrees ! Output variables: REAL(dp), INTENT(OUT) :: x_IM_P_prime ! in meter REAL(dp), INTENT(OUT) :: y_IM_P_prime ! in meter REAL(dp), INTENT(OUT), OPTIONAL :: k_P ! Length scale factor [-], k in Snyder (1987) ! Local variables: REAL(dp) :: phi_P ! in radians REAL(dp) :: lambda_P ! in radians REAL(dp) :: q_P ! in radians, q in Snyder (1987) REAL(dp) :: beta REAL(dp) :: B ! For North and South Pole: C%lambda_M = 0._dp, to generate the correct IM coordinate ! system, see equation (2.3) or equation (A.53) in Reerink et al. (2010). IF(C%polar_projection) THEN ! The polar case is excepted from the oblique formula's, see page 187-188 Snyder (1987) IF(PRESENT(k_P)) THEN ! Output: x_IM_P_prime, y_IM_P_prime, k_P CALL polar_laea_projection_ellipsoid_snyder(lambda, phi, x_IM_P_prime, y_IM_P_prime, k_P) ELSE ! Output: x_IM_P_prime, y_IM_P_prime CALL polar_laea_projection_ellipsoid_snyder(lambda, phi, x_IM_P_prime, y_IM_P_prime) END IF ELSE ! The oblique case, see page 160 Snyder (1987) ! Convert longitude-latitude coordinates to radians: phi_P = C%degrees_to_radians * phi lambda_P = C%degrees_to_radians * lambda ! See equation (3-12) on page 187 in Snyder (1987): q_P = (1._dp - C%e**2) * ((SIN(phi_P) / (1._dp - (C%e * SIN(phi_P))**2)) - (1._dp / (2._dp * C%e)) * LOG((1._dp - C%e * SIN(phi_P)) / (1._dp + C%e * SIN(phi_P)))) ! See equation (3-11) on page 187 in Snyder (1987): beta = ASIN(q_P / C%q_polar) ! See equation (24-19) on page 187 in Snyder (1987): B = C%R_q_polar * SQRT(2._dp / (1._dp + SIN(C%beta_M) * SIN(beta) + COS(C%beta_M) * COS(beta) * COS(lambda_P - C%lambda_M))) ! See equation (24-17) and (24-18) on page 187 in Snyder (1987): x_IM_P_prime = B * C%D * COS(beta) * SIN(lambda_P - C%lambda_M) y_IM_P_prime = (B / C%D) * (COS(C%beta_M) * SIN(beta) - SIN(C%beta_M) * COS(beta) * COS(lambda_P - C%lambda_M)) END IF END SUBROUTINE oblique_laea_projection_ellipsoid_snyder SUBROUTINE polar_laea_projection_ellipsoid_snyder(lambda, phi, x_IM_P_prime, y_IM_P_prime, k_P) ! This subroutine projects with Snyder's polar Lambert azimuthal equal-area projection for ! the ellipsoid the longitude-latitude coordinates which coincide with the GCM grid points to ! the rectangular IM coordinate system, with coordinates (x,y). See Snyder (1987) p. 188. ! ! The examples of Snyder (1987) at p. 334-345 with the international ellipsoid are used to ! validate this forward LAEA projection on the ellipsoid for the polar aspect. ! ! For more information about M, C%alpha_stereographic, the center of projection and the used ! projection method see: ! Reerink et al. (2010), Mapping technique of climate fields between GCM's and ice models, GMD ! and ! Snyder (1987), map projections: A working manual, http://pubs.er.usgs.gov/usgspubs/pp/pp1395 USE oblimap_configuration_module, ONLY: dp, C IMPLICIT NONE ! Input variables: REAL(dp), INTENT(IN) :: lambda ! in degrees REAL(dp), INTENT(IN) :: phi ! in degrees ! Output variables: REAL(dp), INTENT(OUT) :: x_IM_P_prime ! in meter REAL(dp), INTENT(OUT) :: y_IM_P_prime ! in meter REAL(dp), INTENT(OUT), OPTIONAL :: k_P ! Length scale factor [-], k in Snyder ! Local variables: REAL(dp) :: phi_P ! in radians REAL(dp) :: lambda_P ! in radians REAL(dp) :: q_P ! in radians, q in Snyder (1987) REAL(dp) :: rho REAL(dp) :: pf ! polar factor: -1.0 for SP and +1.0 for NP IF(C%phi_M == - 90.0_dp * C%degrees_to_radians) THEN pf = -1.0_dp ! The polar factor for the SP ELSE pf = 1.0_dp ! The polar factor for the NP END IF ! Convert longitude-latitude coordinates to radians: phi_P = C%degrees_to_radians * phi lambda_P = C%degrees_to_radians * lambda ! See equation (3-12) on page 187 in Snyder (1987): q_P = (1._dp - C%e**2) * ((SIN(phi_P) / (1._dp - (C%e * SIN(phi_P))**2)) - (1._dp / (2._dp * C%e)) * LOG((1._dp - C%e * SIN(phi_P)) / (1._dp + C%e * SIN(phi_P)))) ! See equation (24-23) and (24-25) on page 188 in Snyder (1987): rho = C%a * SQRT(C%q_polar - q_P * pf) ! See equation (21-30), (21-31) and (24-24) on page 188 in Snyder (1987): x_IM_P_prime = rho * SIN(lambda_P - C%lambda_M) y_IM_P_prime = - rho * COS(lambda_P - C%lambda_M) * pf ! See equation (21-32) on page 188 in Snyder (1987): IF(PRESENT(k_P)) k_P = rho / (C%a * (COS(phi_P ) / SQRT(1.0_dp - (C%e * SIN(phi_P ))**2))) !IF(PRESENT(k_P)) k_P = rho / (C%a * (COS(phi_P * pf) / SQRT(1.0_dp - (C%e * SIN(phi_P * pf))**2))) ! Check if perhaps this is intended by Snyder, but makes no difference. END SUBROUTINE polar_laea_projection_ellipsoid_snyder SUBROUTINE inverse_oblique_laea_projection_ellipsoid_snyder(x_IM_P_prime, y_IM_P_prime, lambda_P, phi_P) ! This subroutine projects with Snyder's inverse oblique Lambert azimuthal equal-area projection for ! the ellipsoid the (x,y) coordinates which coincide with the IM grid points to the longitude-latitude ! coordinate system, with coordinates (lambda, phi) in degrees. ! ! For more information about M, C%alpha_stereographic, the center of projection and the used ! projection method see: ! Reerink et al. (2010), Mapping technique of climate fields between GCM's and ice models, GMD ! and ! Snyder (1987), map projections: A working manual, http://pubs.er.usgs.gov/usgspubs/pp/pp1395 USE oblimap_configuration_module, ONLY: dp, C IMPLICIT NONE ! Input variables: REAL(dp), INTENT(IN) :: x_IM_P_prime ! in meter REAL(dp), INTENT(IN) :: y_IM_P_prime ! in meter ! Output variables: REAL(dp), INTENT(OUT) :: lambda_P ! in degrees REAL(dp), INTENT(OUT) :: phi_P ! in degrees ! Local variables: REAL(dp) :: rho REAL(dp) :: angle_C ! in radians REAL(dp) :: beta ! in radians REAL(dp) :: numerator REAL(dp) :: denumerator IF(C%polar_projection) THEN ! The inverse polar case is excepted from the inverse oblique formula's, see page 190 Snyder (1987) ! Output: lambda_P, phi_P CALL inverse_polar_laea_projection_ellipsoid_snyder(x_IM_P_prime, y_IM_P_prime, lambda_P, phi_P) ELSE ! The inverse oblique case, see page 188-189 Snyder (1987) ! See equation (24-28) on page 189 Snyder (1987): rho = SQRT((x_IM_P_prime / C%D)**2 + (C%D * y_IM_P_prime)**2) ! See equation (24-29) on page 189 Snyder (1987): angle_C = 2._dp * ASIN(rho / (2._dp * C%R_q_polar)) ! See equation (24-30) on page 189 Snyder (1987): beta = ASIN(COS(angle_C) * SIN(C%beta_M) + (C%D * y_IM_P_prime * SIN(angle_C) * COS(C%beta_M) / rho)) ! See equation (3-18) on page 189 instead of equation (3-16) on page 188 Snyder (1987): phi_P = C%radians_to_degrees * (beta + & (C%e**2 / 3._dp + 31._dp * C%e**4 / 180._dp + 517._dp * C%e**6 / 5040._dp) * SIN(2._dp * beta) + & ( 23._dp * C%e**4 / 360._dp + 251._dp * C%e**6 / 3780._dp) * SIN(4._dp * beta) + & ( 761._dp * C%e**6 / 45360._dp) * SIN(6._dp * beta)) ! See equation (20-26) on page 188 Snyder (1987): numerator = x_IM_P_prime * SIN(angle_C) denumerator = C%D * rho * COS(C%beta_M) * COS(angle_C) - C%D**2 * y_IM_P_prime * SIN(C%beta_M) * SIN(angle_C) lambda_P = C%radians_to_degrees * (C%lambda_M + arctangens_quotient(numerator, denumerator)) ! Our choice is to return lambda in the 0-360 degree range: IF(lambda_P < 0._dp) lambda_P = lambda_P + 360._dp ! In case point P coincides with M (see the condition down equation (20-14) on page 186 Snyder (1987): IF(rho == 0._dp) THEN lambda_P = C%radians_to_degrees * C%lambda_M phi_P = C%radians_to_degrees * C%phi_M END IF END IF END SUBROUTINE inverse_oblique_laea_projection_ellipsoid_snyder SUBROUTINE inverse_polar_laea_projection_ellipsoid_snyder(x_IM_P_prime, y_IM_P_prime, lambda_P, phi_P) ! This subroutine projects with Snyder's inverse oblique Lambert azimuthal equal-area projection for ! the ellipsoid the (x,y) coordinates which coincide with the IM grid points to the longitude-latitude ! coordinate system, with coordinates (lambda, phi) in degrees. See Snyder (1987) p. 190. ! ! The examples of Snyder (1987) at p. 336-337 with the international ellipsoid are used to ! validate this inverse SG projection on the ellipsoid for the polar aspect. ! For more information about M, C%alpha_stereographic, the center of projection and the used ! projection method see: ! Reerink et al. (2010), Mapping technique of climate fields between GCM's and ice models, GMD ! and ! Snyder (1987), map projections: A working manual, http://pubs.er.usgs.gov/usgspubs/pp/pp1395 USE oblimap_configuration_module, ONLY: dp, C IMPLICIT NONE ! Input variables: REAL(dp), INTENT(IN) :: x_IM_P_prime ! in meter REAL(dp), INTENT(IN) :: y_IM_P_prime ! in meter ! Output variables: REAL(dp), INTENT(OUT) :: lambda_P ! in degrees REAL(dp), INTENT(OUT) :: phi_P ! in degrees ! Local variables: REAL(dp) :: rho REAL(dp) :: beta ! in radians REAL(dp) :: pf ! polar factor: -1.0 for SP and +1.0 for NP IF(C%phi_M == - 90.0_dp * C%degrees_to_radians) THEN pf = -1.0_dp ! The polar factor for the SP ELSE pf = 1.0_dp ! The polar factor for the NP END IF ! See equation (20-18) on page 190 Snyder (1987): rho = SQRT(x_IM_P_prime**2 + y_IM_P_prime**2) ! See equation (24-32) on page 190 Snyder (1987): beta = pf * ASIN(1.0_dp - rho**2 / (C%a**2 * ( 1.0_dp - ((1.0_dp - C%e**2) / (2.0_dp * C%e)) * LOG((1.0_dp - C%e) / (1.0_dp + C%e)) ))) ! See equation (3-18) on page 189 instead of equation (3-16) on page 188 as described on page 190 Snyder (1987): phi_P = C%radians_to_degrees * (beta + & (C%e**2 / 3._dp + 31._dp * C%e**4 / 180._dp + 517._dp * C%e**6 / 5040._dp) * SIN(2._dp * beta) + & ( 23._dp * C%e**4 / 360._dp + 251._dp * C%e**6 / 3780._dp) * SIN(4._dp * beta) + & ( 761._dp * C%e**6 / 45360._dp) * SIN(6._dp * beta)) ! See equation (20-16) on page 190 Snyder (1987): lambda_P = C%radians_to_degrees * (C%lambda_M + arctangens_quotient(x_IM_P_prime, - y_IM_P_prime *pf)) ! Our choice is to return lambda in the 0-360 degree range: IF(lambda_P < 0._dp) lambda_P = lambda_P + 360._dp ! In case point P coincides with M (see the condition down equation (20-14) on page 186 Snyder (1987): IF(rho == 0._dp) THEN lambda_P = C%radians_to_degrees * C%lambda_M phi_P = C%radians_to_degrees * C%phi_M END IF END SUBROUTINE inverse_polar_laea_projection_ellipsoid_snyder FUNCTION arctangens_quotient(numerator, denumerator) RESULT(angle) USE oblimap_configuration_module, ONLY: dp, C IMPLICIT NONE ! Input variables: REAL(dp), INTENT(IN) :: numerator REAL(dp), INTENT(IN) :: denumerator ! Result variables: REAL(dp) :: angle ! in radians ! Local variables: REAL(dp) :: quadrant_correction ! See note 2 on page ix in Snyder (1987), to distinguish between the quadrants: quadrant_correction = 0._dp IF(denumerator < 0._dp) quadrant_correction = C%pi IF(denumerator == 0._dp) quadrant_correction = 0.5_dp * C%pi IF(numerator < 0._dp) quadrant_correction = - quadrant_correction IF(denumerator == 0._dp) THEN IF(numerator == 0._dp) THEN ! The angle is indetermined, usually zero is taken: angle = 0._dp ELSE angle = 0.5_dp * C%pi * (numerator / ABS(numerator)) END IF ELSE angle = ATAN(numerator / denumerator) + quadrant_correction END IF END FUNCTION arctangens_quotient SUBROUTINE rotation_projection(x_IM, y_IM, x_IM_prime, y_IM_prime) ! This subroutine transforms the 2D coordinates which are projected with a rotation from ! a rectangular IM coordinate system (x,y) to another rectangular IM prime coordinate ! system (x',y') USE oblimap_configuration_module, ONLY: dp, C IMPLICIT NONE ! Input variables: REAL(dp), INTENT(IN) :: x_IM ! in meter REAL(dp), INTENT(IN) :: y_IM ! in meter ! Output variables: REAL(dp), INTENT(OUT) :: x_IM_prime ! in meter REAL(dp), INTENT(OUT) :: y_IM_prime ! in meter ! See for a derivation: http://www.youtube.com/watch?v=h11ljFJeaLo x_IM_prime = x_IM * COS(C%theta_rotation_projection) + y_IM * SIN(C%theta_rotation_projection) y_IM_prime = - x_IM * SIN(C%theta_rotation_projection) + y_IM * COS(C%theta_rotation_projection) END SUBROUTINE rotation_projection SUBROUTINE inverse_rotation_projection(x_IM_prime, y_IM_prime, x_IM, y_IM) ! This subroutine transforms the 2D coordinates which are projected with a inverse rotation ! from a rectangular IM prime coordinate system (x',y') to another rectangular IM coordinate ! system (x,y) USE oblimap_configuration_module, ONLY: dp, C IMPLICIT NONE ! Input variables: REAL(dp), INTENT(IN) :: x_IM_prime ! in meter REAL(dp), INTENT(IN) :: y_IM_prime ! in meter ! Output variables: REAL(dp), INTENT(OUT) :: x_IM ! in meter REAL(dp), INTENT(OUT) :: y_IM ! in meter ! This equations are derived by taking a linear combination of the rotation projection equations. x_IM = x_IM_prime * COS(C%theta_rotation_projection) - y_IM_prime * SIN(C%theta_rotation_projection) y_IM = x_IM_prime * SIN(C%theta_rotation_projection) + y_IM_prime * COS(C%theta_rotation_projection) END SUBROUTINE inverse_rotation_projection END MODULE oblimap_projection_module