The Alpha GEOID2022 prototype data is available for download in two formats, ASCII and .b. Additional grids and tools will be available in the near future. Use the buttons and instructions below to download and read the data.

Data Releases

Instructions for reading data ASCII Data sets

• read (*,*) xlatmin,xlonmin,dphi,dlam,ilat,ilon
• Do I=1,ilat
• xlat=xlatmin+(i-1)*dphi
• read(*,*) (undu(i,j),j=1,ilon)
• do j=1,ilon
• xlon=xlonmin+(j-1)*dlam
• ENDDO
• ENDDO

Instructions for reading the .b data set

• real*8 xlatmin,xlonmin,dphi,dlam
• real*4 undu(5401,10801)
• read (*) xlatmin,xlonmin,dphi,dlam,ilat,ilon
• Do I=1,ilat
• xlat=xlatmin+(i-1)*dphi
• read(*) (undu(i,j),j=1,ilon)
• do j=1,ilon
• xlon=xlonmin+(j-1)*dlam
• ENDDO
• ENDDO

The pseudo-code for combining SGEOID and DGEOID

At a user provided location (latitude/longitude), both SGEOID and DGEOID grids are interpolated and then combined as follows based on a user-specified epoch (mjdn):

GEOID = SGEOID + DGEOID*(mjdn-58849)/365.25

where mjdn is the modified Julian day determined according to the following:

• #The // symbol denotes integer division, e.g. 4//3 = 1 and 2//3 = 0.
• #MJD 58849 corresponds to midnight, January 1st, 2020 or the 2020.0 epoch of the static geoid
• a = (14 - month)//12
• y = year + 4800 - a
• m = month + 12*a - 3
• jdn = day + (153*m+2)//5 + 365*y + y//4 - y//100 + y//400 - 32045
• mjdn = jdn - 2400001