Hi,

I'm trying to run CMAQ with a grid in mercator projection.

I am preparing the input data and I have reprojected latlon (epsg:4326) data to my mercator projection with PROJ library.
Documentation/Users_Guide says I should use the following srs definition in order to reproject properly my data:
Mercator: "+proj=merc +a=6370000.0 +b=6370000.0 +lat_ts=$P_ALP +lon_0=$P_GAM"

With $P_ALP and $P_GAM given in the GRIDDESC file.

But when I do that it doesn't exactly match the grid generated by MCIP nor the grid of the wrfout file.

I have looked the code and I find two curious things:

(1) in ll2xy_merc.f90 it uses USE const, ONLY: rearth but in the const_mod.f90 rearth isn't defined. I dont know where it extracts the rearth.

(2) the ll2xy_merc (phi, lambda, lambda0, xx, yy) subroutine only only has lambda0 (center longitude [deg]) as projection argument, but in the documentation that I cited above i have $P_ALP and $P_GAM that represents the latitude of true scale and longitude of the central meridian respectively (according the ioapi documentation ).

Any help would be appreciated

I leave here mi griddesc file and the PROJ srs definition that I am trying to use:
GRIDDESC:

' '
'PAPILA'
  7         0.000         0.000       -61.000       -61.000         0.000
' '
'PAPILAGRID'
'PAPILA'  -3510000.000  -7631603.000     27000.000     27000.000  260  337    1
' '

SRS of Input Grids: epsg:4326
SRS of Output Grids: +proj=merc +lat_ts=0.000 +lon_0=-61.000 +a=6370000.0 +b=6370000.0 +units=m