[Proj] Create custum projection definition PROJ4 for rwanda

[Lavver]

Hi,

I'm struggling to create a custom projection definition for QGis for the
national system used for Rwanda. I am new to the PROJ.4 syntax. 

The ArcView prj file (which works fine) shows:
PROJCS["Rwanda1",GEOGCS["GCS_Clarke_1880",DATUM["D_Clarke_1880",
SPHEROID["Clarke_1880",6378249.138,293.466307656]],
PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],
PROJECTION["Gauss_Kruger"],
PARAMETER["False_Easting",500000.0],PARAMETER["False_Northing",10000000.0],
PARAMETER["Central_Meridian",30.0],PARAMETER["Scale_Factor",0.9999],
PARAMETER["Latitude_Of_Origin",0.0],UNIT["Meter",1.0]]

I translated it to 

+proj=tmerc +ellps=clrk80 +a=6378249.138 +rf=293.466307656 +lon_0=30
+k=0.999900 +units=m +x_0=500000 +y_0=10000000

But I'm still 200m to 300m away from reality

The following WGS84 N/E coordinates should give the projected Coordinates
-1.57741 N /29.93690 E   =>    9825897/492907
-1.57763 N /29.93723 E   =>    9825873/492943
-1.61141 N /29.92847 E   =>    9822138/491968

Could someone help me please ? Maybe  I am omitting a parameter...

How can I adjust the parameters? 

Cheers

Lavuun





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