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<br>Hello all
<p>being unfamiliar with cartographic projections, I hope I won't bother
you with too naive questions.
<p>I have to process together data of different nature and sources:
<br> * satellite (landsat ETM) data, geocorrected (level
1G) , delivered in UTM projection and unspecified ellipsoid -in which case
I assume WGS84
<br> * data given in latitude/longitude for WGS84
<br> * data from ground based stations, delivered in
the local co-ordinate system, in my case (former East Germany):
<br>
Projection: Gauss Krueger in 6° stripes (or Transverse Mercator)
<br>
projection parameters: central meridian 15E false northing 3,500,000m
<br>
Ellipsoid: Krassowsky with Pulkovo Datum (dX=28, dY=-130 dZ=-95)
<p>then come my questions:
<br>-up to version 4.3, proj was restricted to projections only, within
the same ellipsoid/datum system. It seems that the newer version -and program
cs2cs- is able to do the job. Am I right, or is cs2cs also restricted to
one ellipsoid at a time?
<p>-to check my results I was provided with some checked remarkable points,
which co-ordinates are known in lat/long and in the local system.
<br>I was never able to find these results with proj/cs2cs
<br>Example:
<br>"ground truth": geographical, WGS84: 52.4172632N 13.6254409E becomes
y=3406605m x=5810804m on GK/Krassowsky etc
<p>The command
<br>cs2cs +ellps=WGS84 +proj=latlong +to +ellps=krass +proj=tmerc
+lon_0=15 +x_0=3500000
<br>gives me approximately the same figures, yet slighty different:
<br>y=3406478.97 x=5810764.06 (difference is 40m in x and 126m
in y)
<p>-although this difference might be sufficiently small for my application
I would be glad to know if it is normal or much too large, in comparison
to cartography standards
<br>-the difference in x and y looks very much the same as the Pulkovo
datum. I'm not sure of the meaning of this datum: is it a shift from Krassovsky
ellipsoid or from WGS84? In the first case, how can I tell it to cs2cs,
and in the second case, why the same cs2cs command with datum specified
as +towgs84=28,-130,-95
<br>gives me absurd results (e.g. x=3500000.00 y=10002137.50)
<p>-last but not least, wanting to check my command before bothering you,
I've asked for more info with option -v, and look at what is said about
ellipsoid:
<br>(with above cs2cs command, option -v added)
<br># ---- From Coordinate System ----
<br>#Lat/long (Geodetic)
<br>#
<br># +ellps=WGS84 +proj=latlong
<br># ---- To Coordinate System ----
<br>#Transverse Mercator
<br># Cyl, Sph&Ell
<br># +ellps=krass +proj=tmerc +lon_0=15 +x_0=3500000
<br>#--- following specified but NOT used
<br># +ellps=WGS84
<p>how do I have to understand the last comment?
<p>Many thanks for your help
<p>Jean-Paul Berroir
<p>PS: I'm using the proj package version 4.4.4 on a lunix i686 machine
<pre>--
----------------------
AIR project - INRIA - BP 105 - F78153 Le Chesnay Cedex
Tel: +33 1 3963 5703 Fax: +33 1 3963 5880
jean-paul.berroir@inria.fr</pre>
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