<html><head></head><body bgcolor="#FFFFFF"><div><br><br>Sent from my iPadiola</div><div><br>On 14/08/2012, at 21:08, Clifford J Mugnier <<a href="mailto:cjmce@lsu.edu">cjmce@lsu.edu</a>> wrote:<br><br></div><div></div><blockquote type="cite"><div>
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<p><font size="2">Zoltan,</font></p>
<p><font size="2"></font> </p>
<p><font size="2">All of the </font><span style="FONT-FAMILY: 'Times New Roman','serif'; FONT-SIZE: 10pt; mso-bidi-font-size: 12.0pt; mso-fareast-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA">Moçambican
borders were surveyed by British Royal Engineers in the early 1900's and therefore ONLY the borders are on the Cape Datum, Clarke 1880 ellipsoid. In regards to the interior of the of the country, all native classical triangulation was indeed referenced to
the Clarke 1866 ellipsoid for the Tete Datum of 1960, the Madzansua Datum of 1904, and the Observatorio Campo Rodriques Datum of 1907.</span></p>
<p><span style="FONT-FAMILY: 'Times New Roman','serif'; FONT-SIZE: 10pt; mso-bidi-font-size: 12.0pt; mso-fareast-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA"></span> </p>
<p><span style="FONT-FAMILY: 'Times New Roman','serif'; FONT-SIZE: 10pt; mso-bidi-font-size: 12.0pt; mso-fareast-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA">The "Arc of the 30th Meridian Survey"
did not touch the country.</span></p></div></div></blockquote><div><br></div><br><blockquote type="cite"><div><div style="direction: ltr;font-family: Times New Roman;color: #000000;font-size: x-small;">
<p><span style="FONT-FAMILY: 'Times New Roman','serif'; FONT-SIZE: 10pt; mso-bidi-font-size: 12.0pt; mso-fareast-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA"></span></p>
<p><span style="FONT-FAMILY: 'Times New Roman','serif'; FONT-SIZE: 10pt; mso-bidi-font-size: 12.0pt; mso-fareast-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA">In 1995, Norway Mapping did a comprehensive
readjustment of the country called MOZNET/ITRF94.</span></p></div></div></blockquote><div><br></div><div>... which was re-observed in 2011 by a Moçambique/Portuguese mission (I participated on it) but don't know if the results are already available.</div><br><blockquote type="cite"><div><div style="direction: ltr;font-family: Times New Roman;color: #000000;font-size: x-small;">
<p><span style="FONT-FAMILY: 'Times New Roman','serif'; FONT-SIZE: 10pt; mso-bidi-font-size: 12.0pt; mso-fareast-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA"></span> </p>
<p><span style="FONT-FAMILY: 'Times New Roman','serif'; FONT-SIZE: 10pt; mso-bidi-font-size: 12.0pt; mso-fareast-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA">As of September 1999 when I wrote
my <strong><em>Grids & Datums </em></strong>column on the country, no geoid had been computed for the country. Your best bet is likely EGM96 or a variant thereof for a guess of the geoid there.</span></p></div></div></blockquote><div><br></div><div>Be aware that there are large differences (~1 meter) between EGM96 and EGM2008 solutions in the central part of Moçambique. I had a paper where that is clearly shown but don't find it anymore.</div><div><br></div><div>Joaquim</div><div><br></div><br><blockquote type="cite"><div><div style="direction: ltr;font-family: Times New Roman;color: #000000;font-size: x-small;">
<p><br>
<br>
</p>
<div style="FONT-FAMILY: Tahoma; FONT-SIZE: 13px">
<p><font face="Copperplate Gothic Bold">Clifford J. Mugnier, c.p., c.m.s.</font></p>
<p><font face="Copperplate Gothic Bold">Chief of Geodesy</font></p>
<p><font face="Copperplate Gothic Bold">LSU Center for GeoInformatics (ERAD 266)</font></p>
<p><font face="Copperplate Gothic Bold">Dept. of Civil Engineering (P.F. Taylor 3531)</font></p>
<p><font face="Copperplate Gothic Bold">LOUISIANA STATE UNIVERSITY</font></p>
<p><font face="Copperplate Gothic Bold">Baton Rouge, LA 70803</font></p>
<p><font face="Copperplate Gothic Bold">Academic: (225) 578-8536</font></p>
<p><font face="Copperplate Gothic Bold">Research: (225) 578-4578</font></p>
<p><font face="Copperplate Gothic Bold">Cell: (225) 328-8975</font></p>
<p><font face="Copperplate Gothic Bold">honorary lifetime member, lsps</font></p>
<p><font face="Copperplate Gothic Bold">fellow emeritus, asprs</font></p>
<p><font face="Copperplate Gothic Bold">member, apsg</font></p>
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<p>________________________________________<br>
From: <a href="mailto:proj-bounces@lists.maptools.org">proj-bounces@lists.maptools.org</a> [<a href="mailto:proj-bounces@lists.maptools.org">proj-bounces@lists.maptools.org</a>] on behalf of Zoltan Szecsei [<a href="mailto:zoltans@geograph.co.za">zoltans@geograph.co.za</a>]<br>
Sent: Tuesday, August 14, 2012 11:06 AM<br>
To: Mikael Rittri<br>
Cc: PROJ.4 and general Projections Discussions<br>
Subject: Re: [Proj] Gauss conformal Lo33 on Clarke 1880 Cape Datum to WGS84 UTM36S - NTv2 file needed.<br>
<br>
Hi Again,<br>
<br>
I am struggling to locate a copy of the NTv2 file for Clarke 1880 Cape<br>
Datum to WGS84<br>
<br>
I have not had any luck with either Google, or the contacts mentioned in<br>
the article pointed to (below) by Mikael, so please could someone give<br>
me a link to download from, or perhaps send it to me via<br>
<a href="http://transferbigfiles.com">transferbigfiles.com</a> or similar method.<br>
<br>
I have no idea how big, or what extents are in these NTv2 grid files, as<br>
I have never used them before.<br>
<br>
To this end, my area of interest is in Maputo (Mozambique), and<br>
Mozambique apparently uses Clarke 1866 (not 1880) - but the surveyor<br>
"swears blind" that the coords are on "1880" and not "1866".<br>
<br>
This begs the question:<br>
Do the extents of this Clarke 1880 NTv2 grid stop at the South African<br>
border (some 50Km west of my area of interest), or do they cover Maputo<br>
sufficiently?<br>
<br>
<br>
Thanks & kind regards,<br>
Zoltan<br>
<br>
<br>
<br>
<br>
On 2012/07/26 21:42, Mikael Rittri wrote:<br>
> Hello Zoltan.<br>
> Yes, as you say, the traditional transverse mercator projections for Southern Africa have<br>
> axes positive west and south. This can be handled in Proj 4.8.0 (see <a href="http://trac.osgeo.org/proj/wiki/TMSO">http://trac.osgeo.org/proj/wiki/TMSO</a> ).<br>
> However, since both your example coordinates are negative, I think you have data in a less traditional<br>
> but more GIS-friendly variant, where the axes go east and north and the traditional coordinate values<br>
> have been negated.<br>
><br>
> Another problem is caused by the Cape datum having distortions that are not handled well<br>
> by a simple Helmert datum shift ( +towgs84 in Proj.4). Such a datum shift will have errors up to 15 meters,<br>
> perhaps more. You can get much better accuracy from a grid shift file. So I think your source CRS<br>
> is best constructed as<br>
><br>
> +proj=tmerc +lon_0=33 +a=6378249.145 +b=6356514.966398753 +nadgrids=SA.gsb<br>
><br>
> where SA.gsb is an NTv2 grid shift file from Cape to Hartebeesthoek94 (or to WGS84),<br>
> covering South Africa. To find out where you can download it, see<br>
><br>
> <a href="http://eepublishers.co.za/article/datum-transformations-using-the-ntv2-grid.html">http://eepublishers.co.za/article/datum-transformations-using-the-ntv2-grid.html</a><br>
><br>
> About your target CRS, I don't think there is an EPSG code for the combination of Hartebeesthoek94 and<br>
> a UTM projection. But since H94 is the same as WGS84 except for tectonic motion, I think you<br>
> can use WGS84 / UTM zone 36S, which can be defined as<br>
><br>
> +init=epsg:32736<br>
><br>
> Hope this helps,<br>
><br>
> Mikael Rittri<br>
> Carmenta<br>
> Sweden<br>
> <a href="http://www.carmenta.com">http://www.carmenta.com</a><br>
><br>
> 26 jul 2012 kl. 17:14 skrev "Zoltan Szecsei" <<a href="mailto:zoltans@geograph.co.za">zoltans@geograph.co.za</a>>:<br>
><br>
>> Hi Everyone,<br>
>> I have some orthos and some 3D vector data that I need to reproject from<br>
>> Clarke 1880 Cape Datum, Lo33 to WGS84 Hartebeeshoek94 datum UTM 36S.<br>
>><br>
>> I'm hoping to use gdalwarp (with VRT) and ogr2ogr, but I cannot find the<br>
>> input projection codes.<br>
>><br>
>> Please can someone provide some guidance on this?<br>
>> Maybe I have to define them? How?<br>
>><br>
>> The jpw files for the orthos are typically:<br>
>> 0.0500000000000000030<br>
>> 0.0<br>
>> 0.0<br>
>> -0.0500000000000000030<br>
>> -50999.974999999999<br>
>> -2872000.0249999999<br>
>> and you'll probably notice that it is not the usual Gauss Conformal<br>
>> projection, as that would be +ve South and West for this area.<br>
>><br>
>> Once the orthos are done I will be needing to transform (as above) a 3D<br>
>> DGN file and an ASCII DEM file as well. Typical DEM values are:<br>
>> -50400.000,-2872481.000,-2.74<br>
>> -50399.000,-2872481.000,-2.84<br>
>><br>
>> I'd be grateful for some help specifying the input and output projection<br>
>> details (epsg codes??)<br>
>><br>
>> Thanks & regards,<br>
>> Zoltan<br>
>><br>
>><br>
>><br>
>> --<br>
>><br>
>> ===========================================<br>
>> Zoltan Szecsei PrGISc [PGP0031]<br>
>> Geograph (Pty) Ltd.<br>
>> P.O. Box 7, Muizenberg 7950, South Africa.<br>
>><br>
>> 65 Main Road, Muizenberg 7945<br>
>> Western Cape, South Africa.<br>
>><br>
>> 34° 6'16.35"S 18°28'5.62"E<br>
>><br>
>> Tel: +27-21-7884897 Mobile: +27-83-6004028<br>
>> Fax: +27-86-6115323 <a href="http://www.geograph.co.za">www.geograph.co.za</a><br>
>> ===========================================<br>
>><br>
>> _______________________________________________<br>
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>> <a href="mailto:Proj@lists.maptools.org">Proj@lists.maptools.org</a><br>
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<br>
<br>
--<br>
<br>
===========================================<br>
Zoltan Szecsei PrGISc [PGP0031]<br>
Geograph (Pty) Ltd.<br>
P.O. Box 7, Muizenberg 7950, South Africa.<br>
<br>
65 Main Road, Muizenberg 7945<br>
Western Cape, South Africa.<br>
<br>
34° 6'16.35"S 18°28'5.62"E<br>
<br>
Tel: +27-21-7884897 Mobile: +27-83-6004028<br>
Fax: +27-86-6115323 <a href="http://www.geograph.co.za">www.geograph.co.za</a><br>
===========================================<br>
<br>
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