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stevejking | 1 Jul 2011 02:33

Re: Eric Miller VB Wrapper +nadgrids=


stevejking wrote:
> 
> Thanks for your reply.
> I've checked my transformation using cs2cs and it works great replacing
> the +towgs84 bit with
> +nadgrids=c:\proj\nad\OSTN02_TNv2.gsb
> 
> 
Sorry, this worked with cs2cs Rel 4.7.1 (which I had with FWTools), but does
not work with cs2cs Rel 4.4.6 (the version that came with my proj.dll and
proj_api.dll). 4.4.6 returns *    *0.00 as the coordinates. So guess it's a
problem with the proj.dll version not supporting the nadgrids gsb file. 

Think I read somewhere how to make the proj_api.dll from a more recent
proj.dll. Where?

Cheers,
Steve 

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Eric Miller | 1 Jul 2011 03:17
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Re: Eric Miller VB Wrapper +nadgrids=

>>> On 6/30/2011 at 5:33 PM, stevejking <stevejking <at> talktalk.net> wrote:

> stevejking wrote:
>> 
>> Thanks for your reply.
>> I've checked my transformation using cs2cs and it works great replacing
>> the +towgs84 bit with
>> +nadgrids=c:\proj\nad\OSTN02_TNv2.gsb
>> 
>> 
> Sorry, this worked with cs2cs Rel 4.7.1 (which I had with FWTools), but does
> not work with cs2cs Rel 4.4.6 (the version that came with my proj.dll and
> proj_api.dll). 4.4.6 returns *    *0.00 as the coordinates. So guess it's a
> problem with the proj.dll version not supporting the nadgrids gsb file. 
> 
> Think I read somewhere how to make the proj_api.dll from a more recent
> proj.dll. Where?

The source? See the proj_api.zip file.  I'm not sure if the proj_api.dll needs to be recompiled.  It may just
work with newer proj.dll files.

http://ftp.dfg.ca.gov/Public/BDB/Tools/proj4/
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Staff Programmer
CA Dept. of Fish & Game

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Jan Hartmann | 1 Jul 2011 12:47
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Re: Müffling

Thanks Irwin, very interesting links, especially the georeferenced map sheets at the NRW Geoportal. I wonder how they did the georeferencing: it looks quite good, but not optimal. They probably chose some reference points on each sheet and based on those rubber-sheeted them. I'm still working on a direct georeferencing procedure from the original UTM projection (based on the Paris meridian) to the modern Gauss-Krüger projection, using the original triangulation data, but to make it really precise we would need the data for the secondary triangles, and these lie hidden in an archive somewhere in France.

It's a pity they did it only for Nordrhein-Westfalen, and that they didn't provide a WMS service, but that's the way bureaucracies still work. It's a good beginning, though, for further work

Thanks again for the tips,

Jan Hartmann

On 06/30/11 11:08, Irwin Scollar wrote:
An interesting historical link to Müffling and Tranchot which has biographies of both men and some details on their work which I have not seen elsewhere is: http://freepages.history.rootsweb.ancestry.com/~mlcarl/Qu/Karten/Tranchot.htm A link to the work of Müffling and the early Prussian map projection with a brief description of it's history is: http://www.geog.fu-berlin.de/2bik/Kap4/kap4_1-05.php3 It's application in the Rhineland is: http://de.wikipedia.org/wiki/Topographische_Aufnahme_der_Rheinlande Scans of the original maps can be found at the GeoPortal of North-Rhine Westphalia: http://www.tim-online.nrw.de/tim-online/initParams.do;jsessionid=615820C15DD0F8AB73AD2368A8295302 under the topic Historische Karten-Tranchot 1801-1828 While searching, I also learned from the Polish historical military mapping site: http://english.mapywig.org/news.php that early Imperial Russian maps used the Müffling polyhedric projection: http://english.mapywig.org/Russian_and_Soviet_maps_EN.htm Please post additional links related to the theme of Müffling's work. Irwin Scollar _______________________________________________ Proj mailing list Proj <at> lists.maptools.org http://lists.maptools.org/mailman/listinfo/proj 
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stevejking | 1 Jul 2011 14:27

Re: Eric Miller VB Wrapper +nadgrids=


Eric Miller-4 wrote:
> 
> I'm not sure if the proj_api.dll needs to be recompiled.  It may just work
> with newer proj.dll files.
> 
> 
I tried a few newer proj.dll files, but your api only appears to work with
the 4.4.6 version it was made for.
Recompiling is beyond my current skill, so I'll stick with the 7 parameter
towgs84 translations for now.
Would be interested if you or anyone else recompiles against the newer
proj.dll to support NTv2 files.

Thanks for your help, and for sharing your api with the world.
Regards,
Steve

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Noel Zinn (cc | 2 Jul 2011 17:42
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Re: Müffling

Excellent.  Thanks, Irwin.  Bing translation does a remarkable job on those 
among these that need it (college German being many years behind me).  Not 
so well on the autobiography, just an image.  I'm particularly interested in 
...

http://www.geog.fu-berlin.de/2bik/Kap4/kap4_1-05.php3

... and the stitching of the polyhedron together.  Ought to be done in ECEF.

Noel

Noel Zinn, Principal, Hydrometronics LLC
+1-832-539-1472 (office), +1-281-221-0051 (cell)
noel.zinn <at> hydrometronics.com (email)
http://www.hydrometronics.com (website)

-----Original Message----- 
From: Irwin Scollar
Sent: Thursday, June 30, 2011 4:08 AM
To: proj <at> lists.maptools.org
Subject: [Proj] Müffling

An interesting historical link to Müffling and
Tranchot which has biographies of both men and
some details on their work which I have not seen elsewhere is:

http://freepages.history.rootsweb.ancestry.com/~mlcarl/Qu/Karten/Tranchot.htm

A link to the work of Müffling and the early
Prussian map projection with a brief description of it's history is:

http://www.geog.fu-berlin.de/2bik/Kap4/kap4_1-05.php3

It's application in the Rhineland is:

http://de.wikipedia.org/wiki/Topographische_Aufnahme_der_Rheinlande

Scans of the original maps can be found at the
GeoPortal of North-Rhine Westphalia:

http://www.tim-online.nrw.de/tim-online/initParams.do;jsessionid=615820C15DD0F8AB73AD2368A8295302

under the topic Historische Karten-Tranchot 1801-1828

While searching, I also learned from the Polish
historical military mapping site:

http://english.mapywig.org/news.php

that early Imperial Russian maps used the Müffling polyhedric projection:

http://english.mapywig.org/Russian_and_Soviet_maps_EN.htm

Please post additional links related to the theme of Müffling's work.

Irwin Scollar

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Irwin Scollar | 3 Jul 2011 16:09
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Müffling & Maps

A very good history of map making in Prussia and later the rest of 
Germany going back to the very beginning is:

http://www.geog.fu-berlin.de/2bik/index.shtml

Chapter 4 contains the link on geodesy I posted previously.  It is 
the catalog of an exhibition on map making in Berlin and Brandenburg 
at the State Library of Berlin and the Free University of 
Berlin.  Click on the Links button at the top of the page for much more.

For more links than anyone may have time to read:

http://www.maphistory.info/index.html

although with limited coverage of non-English sites.

Irwin Scollar

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Charles Karney | 4 Jul 2011 21:07

Analyzing the bumps in the EGM2008 geoid

Partly in response to Mikael Rittri's questions about compressing the
data files for the EGM models, I looked into seeing how well EGM2008 is
approximated by a few terms in its spherical harmonic expansion.  The
quick answer is not very well.  The bumps in EGM2008 are at all scales
and the coefficients in the spherical harmonic expansion decay very
slowly.

However, I thought it worth reporting on the magnitudes of the low order
terms.  Recall that the range in geoid heights (in meters) relative to
WGS84 is about [-107, 86].

The lowest order terms, Y00, Y10, Y11, Y20, Y21 are all small (less than
0.5m), "by construction".  (The volume if WGS84 is about right, the COM
of the geoid nearly matches WGS84, the flattening nearly matches WGS84.)

The biggest spherical harmonic component is the Y22 term, which is the
component that makes WGS84 into a triaxial ellipsoid.  This makes the
equator an ellipse with major/minor equatorial axes

   6378137 +/- 35 meters

The major axis is lon = -15, 165; the minor axis is lon = -105, 75.  The
amount EGM2008 deviates from this triaxial shape (WGS84 + Y22 term) is
[-72, 70].  The reason that a triaxial model of the earth is not useful
is that you add a lot of mathematical complexity going from an oblate
ellipsoid to a triaxial ellipsoid and yet you have not gained much
(about 25%) in how well you approximate the geoid.

The next biggest contributions are the Y3m components which together
with their amplitudes (meters) above/below WGS84 are

     Y31:  +/- 29
     Y33:  +/- 21
     Y30:  +/- 16
     Y32:  +/- 14

These results were derived by taking spherical harmonic moments of the
gridded EGM2008 geoid numerically using the longitude and geographic
co-latitude as the independent variables.

I found it necessary to carry out these integrals directly rather than
using the spherical harmonic expansions provided by the NGA because the
NGA provides two expansions: one for the gravitational potential and
another for an undulation correction, and both of these use geocentric
co-latitude.  I found it simplest just to perform the analysis on the
geoid height directly.

--

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SRI International, Princeton, NJ 08543-5300
Tel: +1 609 734 2312
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Charles Karney | 4 Jul 2011 21:13

Re: Analyzing the bumps in the EGM2008 geoid

I should have included the definition I used for spherical harmonics
(since different definitions are used in different fields).  I use the
DLMF definition given in

   http://dlmf.nist.gov/14.30.E1
   http://dlmf.nist.gov/14.30.E3
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Charles Karney | 4 Jul 2011 22:11

Differential behavior of geodesics

I've worked out some relationships between reduced lengths and geodesic
scales which I give here...

The story so far: Consider a geodesic from point 1 (azimuth azi1) to
point 2 with length s12.  Consider a second geodesic of length s12
starting from point 1 with azimuth azi1 + dazi1.  The end of this
geodesic lies a distance m12 * dazi1 from point 2.  It is easy to show
that m12 + m21 = 0.  m12 is called the "reduced length".

Consider a third geodesic of length s12 parallel to the first at point 1
but separated a distance dt1 from it.  At point 2 the geodesics are
separated by M12 * dt1.  M21 is defined likewise.  M12 and M21 are
called the "geodesic scales".

Together m12, M12, and M21 completely define the behavior of all
geodesics near the original one.

Derivatives holding point 1 and azi1 fixed and extending the length of
the geodesic:

    dm12/ds2 = M21
    dM12/ds2 = -(1 - M12*M21)/m12

Addition rules, points 1, 2, and 3 all lie on the same geodesic:

    m23 = m13*M12 - m12*M13
    M23 = M21*M13 + (1 - M12*M21) * m13/m12
    M32 = M31*M12 + (1 - M13*M31) * m12/m13

Hence we get Christoffel's addition rule (Theory of Geodesic Triangles,
Art 16, Eq 5) (points 1, 2, 3, and 4 all lie on the same geodesic):

    m12*m34 + m13*m42 + m14*m23 = 0

In the GIS domain, there an interest in defining "buffer regions" around
shapes.  If point 1 is on the original "reference" boundary, then a
point (point 2) on the buffer boundary is obtained by traveling a
distance s12 along a geodesic normal to the reference curve.  The buffer
boundary is therefore a geodesic parallel of the reference curve.

If the geodesic curvature of the reference curve at point 1 is K1, then
the geodesic curvature at point 2 on the buffer boundary is

    K2 = (M21*K1 - (1 - M12*M21)/m12) / (m12*K1 + M12)

If the reference curve has a corner in it, then K1 -> inf, and

    K2 = M21 / m12

is the curvature of a geodesic circle.  If K1 -> 0 then

    K2 = - (1 - M12*M21) / (M12*m12)

is the curvature of a curve parallel to a geodesic.  The test K2 -> inf
can to used to detect when the buffer boundary self-intersects and can
therefore be simplified.

These results are all general; they apply to all reasonable two
dimensional surfaces (not just ellipsoids of revolution).

--

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SRI International, Princeton, NJ 08543-5300
Tel: +1 609 734 2312
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Michael P Finn | 5 Jul 2011 16:38
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Re: Analyzing the bumps in the EGM2008 geoid


Thank you for this and the previous post. Very interesting.




From: Charles Karney <charles.karney <at> sri.com>
To: PROJ.4 and general Projections Discussions <proj <at> lists.maptools.org>
Date: 07/04/2011 01:59 PM
Subject: Re: [Proj] Analyzing the bumps in the EGM2008 geoid
Sent by: proj-bounces <at> lists.maptools.org




I should have included the definition I used for spherical harmonics
(since different definitions are used in different fields).  I use the
DLMF definition given in

  http://dlmf.nist.gov/14.30.E1
  http://dlmf.nist.gov/14.30.E3
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