[Proj] proj and Dutch RD

tvijlbrief tomtor at xs4all.nl
Tue Oct 17 05:35:53 EDT 2006

```Much confusion, but the following definition will work! I submitted this
as a patch for the epsg file to the libproj maintainers.

<28992> +proj=sterea +lat_0=52.15616055555555 +lon_0=5.38763888888889
+k=0.9999079 +x_0=155000 +y_0=463000 +ellps=bessel
+towgs84=565.040,49.910,465.840,-0.40939,0.35971,-1.86849,4.0772 +units=m
+no_defs  <>

For some reason Oscar van Vlijmen's conversion:

Transformation from Bessel 1841 to WGS84:
dx=565.040; dy=49.910; dz=465.840; rx=0.40939; ry=-0.35971; rz=1.86849;
ds=4.0772;

had the sign of rx,ry and rz reversed!

Tom

====================

Roger Oberholtzer wrote:
>
> On Thu, 2006-01-12 at 00:17 +0200, Martin Vermeer wrote:
>> On Wed, Jan 11, 2006 at 12:43:13PM -0800, Eric Miller wrote:
>> > I think Martin's comment is a little to brief.
>> >
>> > Your source coordinate system is geodetic coordinates using the WGS84
>> Datum (implies WGS84 ellipsoid)
>> > In cs2cs terms:  +proj=latlong +datum=WGS84
>> >
>> > Your destination coordinate system is RD (new)
>> > In cs2cs terms: +proj=sterea +lat_0=52.15616055555555
>> +lon_0=5.38763888888889 +k=0.9999079 +x_0=155000 +y_0=463000
>> +ellps=bessel +units=m +towgs84=593,26,478
>> >
>> > I'm not sure about the signs for the towgs84 parameters (dx,dy,dz),
>> maybe they're supposed to be negative.  Anyway, the +towgs84 tells cs2cs
>> how to transform the WGS84 coordinates (in XYZ space) to whatever the
>> output datum for RD is.  The +towgs84 or +datum for a different target
>> coordinate systems will likely be different.  But, your source definition
>> would stay the same.  If you have some reference coordinates, you can
>> probably work out whether the towgs84 numbers are supposed to be positive
>> or negative (provided those are good values).
>> >
>> > Clear as mud?
>>
>> This is precisely what I meant. Thanks!
>
> But the 'fix' was to change the description of the source lat/longs from
>
> 	+proj=latlong +ellps=WGS84
> to
> 	+proj=latlong +ellps=bessel
>
> After the '+to' I always had +ellps=bessel to describe the desired
> result. That was not changed.
>
> Confusion here continues...
>
>>
>> So play around with those +towgs84 parms, until you can reproduce your
>> reference values. There must be decimetre precision shift values
>> somewhere too, as I know the triangulation to be that precise. They must
>> know at the cadastral survey in Apeldoorn. Here is their on-line
>> transformer:
>>
>
> I have looked at that. In summary, the conversion that does the best
> (almost identical values) is:
>
> +proj=latlong +ellps=bessel +to
> +proj=sterea +lat_0=52.15616055555555 +lon_0=5.38763888888889
> +k=0.9999079 +x_0=155000 +y_0=463000 +ellps=bessel +units=m +no_defs
>
> The one that was off by at least 60 meters was:
>
> +proj=latlong +ellps=wgs84 +to
> +proj=sterea +lat_0=52.15616055555555 +lon_0=5.38763888888889
> +k=0.9999079 +x_0=155000 +y_0=463000 +ellps=bessel +units=m +no_defs
>
> --
> Roger Oberholtzer
> OPQ Systems AB
>
>
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> Proj mailing list
> Proj at lists.maptools.org
> http://lists.maptools.org/mailman/listinfo/proj
>
>

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