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Using Geotiff and Worldfile meta information in Geomap

 
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jvgoor



Joined: 07 Sep 2011
Posts: 42
Location: Maasland, The Netherlands

PostPosted: Sat Apr 14, 2012 5:15 pm    Post subject: Using Geotiff and Worldfile meta information in Geomap Reply with quote

I need some help.

I have some high quality maps of the Netherlands in Geotiff format. Each file also comes with a .GTF and .TFW file with meta information about Chart datum, origin, projection etc.. I need help understanding this information and how to use which parameters from these files in order to read calibrate the image for use in Geomap.

Here is a sample of the information found in the .TFW and GTF files.

.TFW
Code:
4.23322441712827
0.00008160332343
0.00008160332343
-4.23322441712827
105024.94390137499000
553795.82460772095000


.GTF
Code:
Geotiff_Information:
   Version: 1
   Key_Revision: 1.0
   Tagged_Information:
      ModelTiepointTag (2,3):
         0                0                0               
         105024.944       553795.825       0               
      ModelPixelScaleTag (1,3):
         4.23322442       4.23322442       0               
      End_Of_Tags.
   Keyed_Information:
      GTModelTypeGeoKey (Short,1): User-Defined
      GTRasterTypeGeoKey (Short,1): RasterPixelIsPoint
      GTCitationGeoKey (Ascii,18): "PCS Name = RD_New"
      GeographicTypeGeoKey (Short,1): User-Defined
      GeogCitationGeoKey (Ascii,70): "GCS Name = GCS_Amersfoort|Ellipsoid = Bessel_1841|Primem = Greenwich|"
      GeogGeodeticDatumGeoKey (Short,1): Datum_Amersfoort
      GeogAngularUnitsGeoKey (Short,1): Angular_Degree
      GeogSemiMajorAxisGeoKey (Double,1): 6377397.16       
      GeogInvFlatteningGeoKey (Double,1): 299.152813       
      GeogPrimeMeridianLongGeoKey (Double,1): 0               
      PCSCitationGeoKey (Ascii,448): "ESRI PE String = PROJCS["RD_New",GEOGCS["GCS_Amersfoort",DATUM["D_Amersfoort",SPHEROID["Bessel_1841",6377397.155,299.1528128]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.017453292519943295]],PROJECTION["Double_Stereographic"],PARAMETER["False_Easting",155000.0],PARAMETER["False_Northing",463000.0],PARAMETER["Central_Meridian",5.38763888888889],PARAMETER["Scale_Factor",0.9999079],PARAMETER["Latitude_Of_Origin",52.15616055555555],UNIT["Meter",1.0]]"
      ProjLinearUnitsGeoKey (Short,1): Linear_Meter
      End_Of_Keys.
   End_Of_Geotiff.

Datum: 6289/(unknown)
Ellipsoid: 0/(unknown) (6377397.16,6356078.96)
Projection Linear Units: 9001/metre (1.000000m)

Corner Coordinates:
Upper Left    ( 105024.944, 553795.825)
Lower Left    ( 105024.944, 527795.360)
Upper Right   ( 143521.887, 553795.825)
Lower Right   ( 143521.887, 527795.360)
Center        ( 124273.415, 540795.592)


I would realy appreciate your help
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Jaap van Goor
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jvgoor



Joined: 07 Sep 2011
Posts: 42
Location: Maasland, The Netherlands

PostPosted: Mon Apr 16, 2012 3:41 pm    Post subject: Using Geotiff and Worldfile meta information in Geomap (2) Reply with quote

I found the solution to my problem. The maps that I have where not using UTM but RD. RD stands for 'Rijksdriehoeksmeting' and is used in charts for Holland. RD uses a different origin, but can be compared to UTM.
When I got the original grid files from the Dutch official institutions (Rijkswaterstaat and Kadaster) it was relatively easy.

All the eastings and northings in the TFW and GTF files are given in RD coordinates. I can now convert these to latitude and longitude.

I found the data in the TFW file the easiest to use to calculate any pixel in the image to a correct RD coordinate, which in turn can be converted to lat and long. Pixels and a position can then be used as a calibration point.

How to interpret a TFW file can be found here: http://en.wikipedia.org/wiki/World_file
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Jaap van Goor
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hlohning



Joined: 08 Sep 2006
Posts: 277
Location: Austria

PostPosted: Sun Apr 22, 2012 11:40 am    Post subject: Reply with quote

Jaap,

just let me add a short remark: in order transform a particular map datum to GPS (=WKS84) the most general way is to use the Helmert transformation equation which can be applied to the Cartesian coordinates obtained from the original datum (see http://www.linz.govt.nz/geodetic/conversion-coordinates/geodetic-datum-conversion/datum-transformation-equations/index.aspx for details).

The Amersfoort datum uses the Bessel 1841 ellipsoid (a=6377397.155, e2=0.00667437223). The Helmert parameters for the Amersfoort datum are:
dx=565
dy=49.9
dz=465.8
ds=4.08
rx-0.409
ry=0.36
rz-1.869

The Helmert transformations for about 270 different datums will be available in the next release (10.1) of the SDL Suite.

Kind regards,

Hans
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