[GIS] How to convert Lat & Long from Onemap.sg to Google Maps

coordinate systemgoogle mapslatitude longitudewgs84

I have a set of address for Singapore, I would like to take the Lat & Long from onemap.sg (SYV21: X, Y / Easting, Northing) and then store it in my databse , convert into (WGS84: Longitude, Latitude) used by google maps and then display on Google Maps.

I have looked at this — http://sgonemap.codeplex.com/ but could not get much out of it.

It will be really nice if someone can help me on this.

Best Answer

try https://github.com/singachea/Onemap-SVY21-API

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[GIS] Working with Google Maps/ArcMap lat/long

Due to various vagaries in the ArcGIS software, I'm going to tell you to use different coordinate reference systems. That will let you access the predefined transformations and hopefully make your life easier.

Use WGS_1984_Web_Mercator_Auxiliary_Sphere instead. This one uses WGS 1984 for the geographic CRS (aka datum). The one you're using, WGS_1984_Web_Mercator, uses a sphere (GCS_WGS_1984_Major_Auxiliary_Sphere) and there are no predefined transformations for it.

Next, use Monte_Mario_Italy_1 which is the same, just a different name. Pick Monte_Mario_To_WGS_1984_4 for the transformation.

Or if you want to use Roma_1940_Gauss_Boaga_Ovest, you'll have to define a custom transformation that's a copy of Monte_Mario_To_WGS_1984_4.

FROM roma 1940 TO wgs84
Method: Position Vector
X axis translation: -104.1
Y axis translation: -49.1
Z axis translation: -9.9
X axis rotation: 0.971
Y axis rotation: -2.917
Z axis rotation: 0.714
scale difference: -11.68

If you define a custom transformation in ArcMap, you may have to define it FROM wgs84 TO roma 1940. If so, change the signs on all parameters.

[GIS] Conversion of 3 degree UTM zone Easting Northing to WGS-84

I guess you stumbled over this note on page 53:

subsequent civilian adoption of the systems usually ignores the zone prefix to easting. Where this is the case the formulas below do not apply: use the standard TM formula separately for each zone

The formulas on page 54 should only be used if the zone number is written before the false Easting, which is not the case here. So I took only the formulas from p 50ff into Libre Office and got these results:

M0  0           
e1  0.0016649922            
mue1    0.4772587465            
M1  3038553.85538554            
T1  0.2701106629            
C1  0.0059292372            
esq 0.0066822021            
D   0.0183352698            
phi1    0.4793002154            
nue1    6381782.36093598            
rho1    6348382.77011411            
phirad  0.4792124095        phi 27.4568485565
lamrad  1.4867384817        lam 85.1838402406

which returns the same lat and lon on the Everest ellipsoid as

cs2cs +proj=tmerc +lon_0=84 +lat_0=0 +k=0.9999 +a=6377276.345 +b=6356075.41314024 +x_0=500000 +units=m +towgs84=282,726,254 +no_defs +to +proj=longlat +a=6377276.345 +b=6356075.41314024 +towgs84=282,726,254 +no_defs -f "%%.6f"<MUTM88.txt >WGS84out.txt

85.183840   27.456849 1230.000000

Transforming to WGS84 returns:

85.181615   27.457128 1188.383496

which is still not exactly what you expected, but more close than your result.

Best Answer

Related Solutions

[GIS] Working with Google Maps/ArcMap lat/long

[GIS] Conversion of 3 degree UTM zone Easting Northing to WGS-84

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