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#1
f_silva

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Hello

I'm trying to project a bathymetric map of a certain region. I have a plain text file with X, Y and Z values, as this example:

122700, 315000, -14.050000005751
122710, 315000, -14.050000001491
122720, 315000, -14.040000002752
122730, 315000, -14.03000001167
122740, 315000, -14.000000002948

And I would like to overlay this with other images in ArcGis. This file uses a military coordinates system (I believe in English this is it?s correct spelling) with a base in a Modern Hayford-Gauss system, with it's base datum the DT73 - lat 39?41'37.300''
and long 8?07'53.310''.
I'm trying to transform this coordinates in to a geographic system, but I'm having some difficulty finding the perfect algorithm. I thought that the Molodensky would be the best for this case, because I have seen programs that transform this coordinates with this algorithm. But I can't find a script, or an easier function to programme, besides the analytical function, with quite some length. Besides all this, my bathymetric as 245.000 points, and because of this, I have to use a mathematical programme, like matlab to read all this points. Can anyone help me with this?

Thanks

Francisco Silva

#2
Hans van der Maarel

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Francisco,

Do you have any more information about the coordinate system this data is supposed to be in. I couldn't find anything for Hayford-Gauss or DT73.
Hans van der Maarel - Cartotalk Editor
Red Geographics
Email: hans@redgeographics.com / Twitter: @redgeographics

#3
f_silva

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Hello Hans

During the weekend I will combine good base information about my problem and then I will post again what I collect. In the while all I can say is that the base datum is the datum of Melrica, which is the geodesic centre of Portugal, with the coordinates I early mentioned. If you are interested, you can search for “hayford-gauss military” and found information like this one:

“Datum 73
The Geographic Institute of Exercito (IGeoE) uses system HGM (System of Hayford- Military Gauss - the system of cartographic projection) in the production of the Military Topographical Map of Portugal at scale 1/25 000, M888 series. This national series is of bigger scale to cover integrally all the territory and was used in the production of the thematic cartography and planning. This fact has contributed for the spreading of a system whose the coordinates are gotten for conversion from the Datum 73 coordinates and not for direct determination in the geodesic net.

i)Origin Point of the geographic coordinates: Melrica, T.F. n-4
ii) Astronomical Comments: 1964
iii) Orientation: some stations of Laplace
iv) ELLIPSOID HAYFORD
v) Origin of rectangulars: Central point = LATITUDE 39 40' N; LONGITUDE 8 7' 54.862" W Greenwich False North = -86,990 m False East = 180,598 m “

This is just what I found everywhere but nobody says how to transform it to geographic coordinates…
Monday I will post again, by then if you can, take a look on this topic and help me again…

Thanks

Francisco Silva

#4
Martin Gamache

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The Grids & Datum column found in PE&RS has a column for Portugal (april 2002) which may be helpful to you or anyone attempting to help you solve this problem.
http://www.asprs.org/resources/grids/

#5
burwelbo

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Francisco

My guess is its a Gauss Kruger Projection using a Hayford Ellipsoid. I don't know what zone Portugal would be in but I think they are equivalent to UTM. Since you don't have any more information on ther Datum and Projection I would import the points into Arc, convert them to a shape file, assign a Gauss Kruger Projection with the appropriate datum using Hayford and see if it matches your imagery. Then you can reproject the shape file to any projection you want.

http://www.csiss.org...hp/Gauss_Kruger

Good Luck
Bruce

#6
f_silva

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First of all, thank you all for your help. But after some researching I found a program that can help with this task. I found a program (TransCoord) that can make the transformation for a file bigger then 10 points, that was the limit for the web engine of the IGEOE (http://www.igeoe.pt/...adas/trans.aspx). So I belive that I have a solution for my problem now?
Anyway thanks a lot for your help.

Best regards,

Francisco Silva




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