<div dir="ltr"><br><div class="gmail_extra"><br><br><div class="gmail_quote">2013/12/31 <span dir="ltr"><<a href="mailto:proj-request@lists.maptools.org" target="_blank">proj-request@lists.maptools.org</a>></span><br>
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Today's Topics:<br>
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1. Map projection of Portugal (Jose Gon?alves)<br>
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Message: 1<br>
Date: Tue, 31 Dec 2013 00:39:03 +0000<br>
From: Jose Gon?alves <<a href="mailto:jagoncal@gmail.com">jagoncal@gmail.com</a>><br>
Subject: [Proj] Map projection of Portugal<br>
To: "PROJ.4 and general Projections Discussions"<br>
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Dear members of the list<br>
<br>
I would like to put some questions related to map projections being used in<br>
Europe. Most of the European countries are now using map coordinate systems<br>
based on the ETRS89 datum. The Portuguese Geographical Institute has<br>
adopted in 2006, for the continental Portugal, a projection, called<br>
?PT-TM06? (EPSG code 3763), similar to the ones used before with older<br>
geodetic datums (Datum Lisboa and Datum 73). It has, in my opinion, some<br>
annoying characteristics that make users loose time, and even make errors<br>
with costly consequences.<br></blockquote><div> </div><div>We have a similar situation in Berlin.<br></div><div>On the 29.12.1879 Prussia introduced 40 Soldner Systems, which until then were mainly used in Bavaria, Württemberg and Baden-Baden.<br>
</div><div>Most of these Systems were replaced by the 'Gauss-Krüger' System between 1900 and 1935.<br></div><div><br>Berlin however retained the 'Soldner 18' system since the city is on the border between zone 4 and 5 (13 30').<br>
</div><div>Since the Central-Point was based at the 'Müggelberg', which is in the South/East portion of 'Greater Berlin', as it was called after 1920- so that 90% of this area have negative values for the East/West positions and positive value for the North/South positions.<br>
<br></div><div>Since each (before 1920 cities) district was responsible for the creation their maps, each decided for themselves how the negative values would be shown. Most showed only positive numbers that increased from East to West.<br>
</div><div>In 1885 the first high scale Maps of the then city of Berlin (1:4000 Straube) were introduced where a 'Soldner Rathausnetz' was used, bases on 'Soldner 18' with x = -14741.77 and y = 11288.28. <br>
This point was the flag post on the City Hall, so that North/East of the Town Hall had positive numbers and South/West had negative numbers.<br></div><div>The, then cities, surrounding Berlin stilled used 'Soldner 18' with Spandau using 'Solder 19'.<br>
</div><div>Only in 1949 was 'Soldner 18' used in the whole City.<br><br></div><div>At some point a 'Fiktive Punkt' was decided upon. <br>This Imaginary point was 40.000 meters West and 10.000 Meters South of the 'Soldner 18' point. (PARAMETER["false_easting",40000],PARAMETER["false_northing",10000],UNIT["Meter",1])<br>
</div><div>- this insured that all values were positive and different from the formally use positions.<br>This System is called 'Soldner Berlin' (EPSG:3068).<br><br></div><div>But again each decided for themselves what would be used. <br>
There is a 1988 Map of Berlin (West), showing territorial exchanges, where the North/South positions are in 'Solder 18' and the West/ East are in 'Soldner Berlin'.<br><br></div><div>Starting last year, new data created is no longer created using 'Soldner Berlin', but in the Brandenburg System(s) based on ETRS_1989_UTM_Zone_33N <br>
of which there are 3 - the others being:<br>- ETRS89_UTM_Zone33_BB_6 - False_Easting = 500000 (same as ETRS_1989_UTM_Zone_33N)<br>- ETRS89_UTM_Zone33_BB_7 - False_Easting = 3500000<br>- ETRS89_UTM_Zone33_BB_8 - False_Easting = 33500000<br>
<br></div><div>As to whether this will simplify matters, well I have my doubts....<br></div><div><br></div><div>Mark Johnson, Berlin Germany<br></div><div> <br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<br>
The projection is a transverse Mercator, with a central point in the centre<br>
of the country, no scale change, i.e. k_0=1, and no false easting/northing,<br>
so coordinates can be positive or negative. Some old coordinate systems in<br>
other countries also had the origin inside the country or region, but I<br>
think that now, most of them do not have this situation. So, my first<br>
question is if anyone knows of map coordinate systems in use, for<br>
topographic surveying and cadastre, which have negative coordinates.<br>
<br>
The second bad aspect of our new coordinate system is that, being the<br>
projection similar to the older ones, coordinates are also very similar.<br>
Differences are in general smaller than 6 meters, so when one looks at a<br>
coordinate pair it is not obvious if it is EPSG:3763 or older systems<br>
(datum 73, EPSG:27493 or datum Lisboa, EPSG:20791). For many years people<br>
will have to deal with data in the older systems, so making mistakes<br>
becomes very easy. The reasonable approach would have been to add a big<br>
shift so that coordinates are not mistaken, as I think most countries do.<br>
This leads to my second question: does anyone know of similar situations of<br>
very close coordinate systems?<br>
I know that in Belgium a projection was established for ETRS89 (Belge 2005,<br>
EPSG:3447) which had coordinates similar to an older system (EPSG:31300).<br>
Meanwhile a new system was defined with new false easting/northing (Belge<br>
2008, EPSG:3812). Was the change motivated by users?<br>
<br>
Regards and a happy new year<br>
<br>
Jose? Gon?alves<br>
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