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EPSG 205x

12 messages

Andrew de Klerk-2

EPSG 205x

Reply Threaded

Some javascript/style in this post has been disabled (why?)

Can anyone confirm what the correct Proj4 definition is for our Hartebeesthoek projections. The closest I have come up with is (for 2054):

+proj=tmerc +ellips=WGS84 +datum=WGS84 +lon_0=31 +k_0=1 +units=m +no_defs

I have tried on numerous occasions to get someone in the know to say if its wrong or right. I do not know enough about the inner workings of projection systems nor the different options available in the proj4 definitions – so if anyone who knows more than me about either of these can help me/us come up with a definite definition this would help.

Gavin – I know you were looking into this a while ago? Did you get any further?

Thanks

Andrew

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Sives Govender

Re: EPSG 205x

Reply Threaded

Some javascript/style in this post has been disabled (why?)

HI Aslam,

Sorry for cross-posting but can you help on the request below?

Regards,

Sives Govender
Executive Director
EIS-AFRICA

office tel:   +27 12 349 1068
office fax: +27 12 349 2080
mobile:     +27 82 929 5034
skype:      sives.govender
alt. email:

[hidden email]

Postal Address:
Postnet Suite 156
Private Bag X15
Menlo Park
0102
South Africa

Physical Address:
Room 274, Building 4E, CSIR
Meiring Naudé Road
Brummeria
Pretoria
0002
South Africa

>>> "Andrew de Klerk" <[hidden email]> 16/07/2009 14:54 >>>

Can anyone confirm what the correct Proj4 definition is for our Hartebeesthoek projections. The closest I have come up with is (for 2054):

+proj=tmerc +ellips=WGS84 +datum=WGS84 +lon_0=31 +k_0=1 +units=m +no_defs

I have tried on numerous occasions to get someone in the know to say if its wrong or right. I do not know enough about the inner workings of projection systems nor the different options available in the proj4 definitions - so if anyone who knows more than me about either of these can help me/us come up with a definite definition this would help.

Gavin - I know you were looking into this a while ago? Did you get any further?

Thanks

Andrew

_______________________________________________
Africa mailing list
[hidden email]
http://lists.osgeo.org/mailman/listinfo/africa

Jeff McKenna

Re: EPSG 205x

Reply Threaded

In reply to this post by Andrew de Klerk-2

Andrew de Klerk wrote:

> Hi
>
>
>
> Can anyone confirm what the correct Proj4 definition is for our
> Hartebeesthoek projections. The closest I have come up with is (for 2054):
>
> +proj=tmerc +ellips=WGS84 +datum=WGS84 +lon_0=31 +k_0=1 +units=m +no_defs
>
>
>
> I have tried on numerous occasions to get someone in the know to say if
> its wrong or right. I do not know enough about the inner workings of
> projection systems nor the different options available in the proj4
> definitions – so if anyone who knows more than me about either of these
> can help me/us come up with a definite definition this would help.
>
>
>
> Gavin – I know you were looking into this a while ago? Did you get any
> further?
>
>
>
> Thanks
>
> Andrew

Andrew de Klerk-2

RE: EPSG 205x

Reply Threaded

Jeff - It has already asked on this list. I am yet to get a conclusive
definition of what it is from about three different lists.

I guess it is not as clear cut as it seems. I would have also thought that
with the Quantum training session the other day, we would have our own proj4
definitions sorted out. No?

Andrew

-----Original Message-----
From: [hidden email] [mailto:[hidden email]]
On Behalf Of Jeff McKenna
Sent: 21 July 2009 02:08 PM
To: Africa local chapter discussions
Subject: Re: [OSGeo Africa] EPSG 205x

Andrew de Klerk wrote:

> Hi
>
>
>
> Can anyone confirm what the correct Proj4 definition is for our
> Hartebeesthoek projections. The closest I have come up with is (for 2054):
>
> +proj=tmerc +ellips=WGS84 +datum=WGS84 +lon_0=31 +k_0=1 +units=m +no_defs
>
>
>
> I have tried on numerous occasions to get someone in the know to say if
> its wrong or right. I do not know enough about the inner workings of
> projection systems nor the different options available in the proj4
> definitions - so if anyone who knows more than me about either of these
> can help me/us come up with a definite definition this would help.
>
>
>
> Gavin - I know you were looking into this a while ago? Did you get any
> further?
>
>
>
> Thanks
>
> Andrew

graeme mcferren

RE: EPSG 205x

Reply Threaded

Hi Andrew

This question needs a bit of disambiguation (oops, I sound like wikipedia...) and discussion

I remind you btw of the excellent resource www.spatialreference.org

The Hartebeesthoek94 coord system is EPSG:4148 (http://www.spatialreference.org/ref/epsg/4148/ ) defined in proj format as: +proj=longlat +ellps=WGS84 +towgs84=0,0,0,0,0,0,0 +no_defs

Projected systems can of course be based on this, but if you are specifically after the LO flavour of things check out:

http://www.spatialreference.org/ref/epsg/2046/
http://www.spatialreference.org/ref/epsg/2047/
...
http://www.spatialreference.org/ref/epsg/2055/

None of these provide a proj4 definition though, nor can I find one in PostGIS or via OSR, implying to me that it would be difficult to project into these projections if using some FOSS Tools.

I don't think your proj4 style attempt will quite work though, because it does not provide for the necessary southward orientation. LO is a south-oriented Transverse Mercator AFAIK

When resolved, this should be contributed to SpatialReference.org, I think

Regards
Graeme

>>> "Andrew de Klerk" <[hidden email]> 07/21/09 2:30 PM >>>
Jeff - It has already asked on this list. I am yet to get a conclusive
definition of what it is from about three different lists.

I guess it is not as clear cut as it seems. I would have also thought that
with the Quantum training session the other day, we would have our own proj4
definitions sorted out. No?

Andrew

-----Original Message-----
From: [hidden email] [mailto:[hidden email]]
On Behalf Of Jeff McKenna
Sent: 21 July 2009 02:08 PM
To: Africa local chapter discussions
Subject: Re: [OSGeo Africa] EPSG 205x

Andrew de Klerk wrote:

> Hi
>
>
>
> Can anyone confirm what the correct Proj4 definition is for our
> Hartebeesthoek projections. The closest I have come up with is (for 2054):
>
> +proj=tmerc +ellips=WGS84 +datum=WGS84 +lon_0=31 +k_0=1 +units=m +no_defs
>
>
>
> I have tried on numerous occasions to get someone in the know to say if
> its wrong or right. I do not know enough about the inner workings of
> projection systems nor the different options available in the proj4
> definitions - so if anyone who knows more than me about either of these
> can help me/us come up with a definite definition this would help.
>
>
>
> Gavin - I know you were looking into this a while ago? Did you get any
> further?
>
>
>
> Thanks
>
> Andrew

Andrew de Klerk-2

RE: EPSG 205x

Reply Threaded

Hi Graeme

Thanks for the response. Yes, I am well aware of the resource available
through spatialreference. This is where my confusion comes in. if you run
the following:

cs2cs +proj=latlong +datum=WGS84 +to +proj=tmerc +lon_0=31 +datum=WGS84

and then enter:
30.352 -29.623

You will get:
-62758.77 -3278498.65 0.00

This is of course the correct answer. Which immediately tells me that the
definitions in place can handle our projection systems, and it is merely a
factor of syntax. Please correct me if I am wrong.

Andrew

-----Original Message-----
From: [hidden email] [mailto:[hidden email]]
On Behalf Of Graeme McFerren
Sent: 21 July 2009 03:26 PM
To: 'Africa local chapter discussions'
Subject: RE: [OSGeo Africa] EPSG 205x

Hi Andrew

This question needs a bit of disambiguation (oops, I sound like
wikipedia...) and discussion

I remind you btw of the excellent resource www.spatialreference.org

The Hartebeesthoek94 coord system is EPSG:4148
(http://www.spatialreference.org/ref/epsg/4148/ ) defined in proj format as:
+proj=longlat +ellps=WGS84 +towgs84=0,0,0,0,0,0,0 +no_defs

Projected systems can of course be based on this, but if you are
specifically after the LO flavour of things check out:

http://www.spatialreference.org/ref/epsg/2046/
http://www.spatialreference.org/ref/epsg/2047/
...
http://www.spatialreference.org/ref/epsg/2055/

None of these provide a proj4 definition though, nor can I find one in
PostGIS or via OSR, implying to me that it would be difficult to project
into these projections if using some FOSS Tools.

I don't think your proj4 style attempt will quite work though, because it
does not provide for the necessary southward orientation. LO is a
south-oriented Transverse Mercator AFAIK

When resolved, this should be contributed to SpatialReference.org, I think

Regards
Graeme

>>> "Andrew de Klerk" <[hidden email]> 07/21/09 2:30 PM >>>
Jeff - It has already asked on this list. I am yet to get a conclusive
definition of what it is from about three different lists.

I guess it is not as clear cut as it seems. I would have also thought that
with the Quantum training session the other day, we would have our own proj4
definitions sorted out. No?

Andrew

-----Original Message-----
From: [hidden email] [mailto:[hidden email]]
On Behalf Of Jeff McKenna
Sent: 21 July 2009 02:08 PM
To: Africa local chapter discussions
Subject: Re: [OSGeo Africa] EPSG 205x

Andrew de Klerk wrote:

> Hi
>
>
>
> Can anyone confirm what the correct Proj4 definition is for our
> Hartebeesthoek projections. The closest I have come up with is (for 2054):
>
> +proj=tmerc +ellips=WGS84 +datum=WGS84 +lon_0=31 +k_0=1 +units=m +no_defs
>
>
>
> I have tried on numerous occasions to get someone in the know to say if
> its wrong or right. I do not know enough about the inner workings of
> projection systems nor the different options available in the proj4
> definitions - so if anyone who knows more than me about either of these
> can help me/us come up with a definite definition this would help.
>
>
>
> Gavin - I know you were looking into this a while ago? Did you get any
> further?
>
>
>
> Thanks
>
> Andrew

graeme mcferren

RE: EPSG 205x

Reply Threaded

Hi Andrew

A bit of clarification on what I said earlier:

SA's LO system is a modified Transverse Mercator (Gauss Conform) in which your metres South positively increases. To the east of the Central Meridian your values decrease, while to the west they increase and are positive

So your example outputs would be correct for a standard Transverse Mercator , but incorrect for the LO system we use

Graeme

>>> "Andrew de Klerk" <[hidden email]> 07/21/09 4:04 PM >>>
Hi Graeme

Thanks for the response. Yes, I am well aware of the resource available
through spatialreference. This is where my confusion comes in. if you run
the following:

cs2cs +proj=latlong +datum=WGS84 +to +proj=tmerc +lon_0=31 +datum=WGS84

and then enter:
30.352 -29.623

You will get:
-62758.77 -3278498.65 0.00

This is of course the correct answer. Which immediately tells me that the
definitions in place can handle our projection systems, and it is merely a
factor of syntax. Please correct me if I am wrong.

Andrew

-----Original Message-----
From: [hidden email] [mailto:[hidden email]]
On Behalf Of Graeme McFerren
Sent: 21 July 2009 03:26 PM
To: 'Africa local chapter discussions'
Subject: RE: [OSGeo Africa] EPSG 205x

Hi Andrew

This question needs a bit of disambiguation (oops, I sound like
wikipedia...) and discussion

I remind you btw of the excellent resource www.spatialreference.org

The Hartebeesthoek94 coord system is EPSG:4148
(http://www.spatialreference.org/ref/epsg/4148/ ) defined in proj format as:
+proj=longlat +ellps=WGS84 +towgs84=0,0,0,0,0,0,0 +no_defs

Projected systems can of course be based on this, but if you are
specifically after the LO flavour of things check out:

http://www.spatialreference.org/ref/epsg/2046/
http://www.spatialreference.org/ref/epsg/2047/
...
http://www.spatialreference.org/ref/epsg/2055/

None of these provide a proj4 definition though, nor can I find one in
PostGIS or via OSR, implying to me that it would be difficult to project
into these projections if using some FOSS Tools.

I don't think your proj4 style attempt will quite work though, because it
does not provide for the necessary southward orientation. LO is a
south-oriented Transverse Mercator AFAIK

When resolved, this should be contributed to SpatialReference.org, I think

Regards
Graeme

>>> "Andrew de Klerk" <[hidden email]> 07/21/09 2:30 PM >>>
Jeff - It has already asked on this list. I am yet to get a conclusive
definition of what it is from about three different lists.

I guess it is not as clear cut as it seems. I would have also thought that
with the Quantum training session the other day, we would have our own proj4
definitions sorted out. No?

Andrew

-----Original Message-----
From: [hidden email] [mailto:[hidden email]]
On Behalf Of Jeff McKenna
Sent: 21 July 2009 02:08 PM
To: Africa local chapter discussions
Subject: Re: [OSGeo Africa] EPSG 205x

Andrew de Klerk wrote:

> Hi
>
>
>
> Can anyone confirm what the correct Proj4 definition is for our
> Hartebeesthoek projections. The closest I have come up with is (for 2054):
>
> +proj=tmerc +ellips=WGS84 +datum=WGS84 +lon_0=31 +k_0=1 +units=m +no_defs
>
>
>
> I have tried on numerous occasions to get someone in the know to say if
> its wrong or right. I do not know enough about the inner workings of
> projection systems nor the different options available in the proj4
> definitions - so if anyone who knows more than me about either of these
> can help me/us come up with a definite definition this would help.
>
>
>
> Gavin - I know you were looking into this a while ago? Did you get any
> further?
>
>
>
> Thanks
>
> Andrew

Andrew,

Maybe you should ask this question on the Proj mailing list
(http://lists.maptools.org/mailman/listinfo/proj), I bet that is where
you'll find help.

-jeff

--
Jeff McKenna
FOSS4G Consulting and Training Services
http://www.gatewaygeomatics.com/

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Andrew de Klerk-2

RE: EPSG 205x

Reply Threaded

Ok thanks Graeme

So the long and the short of it is we cannot use the FOSS tools to their
full potential until the proj library has been updated to accommodate our
projection systems. Is that correct?

We have managed to get around this in the past by either converting data to
dd and using 4148 or to a utm zone 35 or 36.

If the proj library does need to be updated, then I think considering the
governments push towards FOSS CDSM needs to invest some time and money in
assisting with this. My 2c anyway

Andrew

-----Original Message-----
From: [hidden email] [mailto:[hidden email]]
On Behalf Of Graeme McFerren
Sent: 21 July 2009 04:31 PM
To: 'Africa local chapter discussions'
Subject: RE: [OSGeo Africa] EPSG 205x

Hi Andrew

A bit of clarification on what I said earlier:

SA's LO system is a modified Transverse Mercator (Gauss Conform) in which
your metres South positively increases. To the east of the Central Meridian
your values decrease, while to the west they increase and are positive

So your example outputs would be correct for a standard Transverse Mercator
, but incorrect for the LO system we use

Graeme

>>> "Andrew de Klerk" <[hidden email]> 07/21/09 4:04 PM >>>
Hi Graeme

Thanks for the response. Yes, I am well aware of the resource available
through spatialreference. This is where my confusion comes in. if you run
the following:

cs2cs +proj=latlong +datum=WGS84 +to +proj=tmerc +lon_0=31 +datum=WGS84

and then enter:
30.352 -29.623

You will get:
-62758.77 -3278498.65 0.00

This is of course the correct answer. Which immediately tells me that the
definitions in place can handle our projection systems, and it is merely a
factor of syntax. Please correct me if I am wrong.

Andrew

-----Original Message-----
From: [hidden email] [mailto:[hidden email]]
On Behalf Of Graeme McFerren
Sent: 21 July 2009 03:26 PM
To: 'Africa local chapter discussions'
Subject: RE: [OSGeo Africa] EPSG 205x

Hi Andrew

This question needs a bit of disambiguation (oops, I sound like
wikipedia...) and discussion

I remind you btw of the excellent resource www.spatialreference.org

The Hartebeesthoek94 coord system is EPSG:4148
(http://www.spatialreference.org/ref/epsg/4148/ ) defined in proj format as:
+proj=longlat +ellps=WGS84 +towgs84=0,0,0,0,0,0,0 +no_defs

Projected systems can of course be based on this, but if you are
specifically after the LO flavour of things check out:

http://www.spatialreference.org/ref/epsg/2046/
http://www.spatialreference.org/ref/epsg/2047/
...
http://www.spatialreference.org/ref/epsg/2055/

None of these provide a proj4 definition though, nor can I find one in
PostGIS or via OSR, implying to me that it would be difficult to project
into these projections if using some FOSS Tools.

I don't think your proj4 style attempt will quite work though, because it
does not provide for the necessary southward orientation. LO is a
south-oriented Transverse Mercator AFAIK

When resolved, this should be contributed to SpatialReference.org, I think

Regards
Graeme

>>> "Andrew de Klerk" <[hidden email]> 07/21/09 2:30 PM >>>
Jeff - It has already asked on this list. I am yet to get a conclusive
definition of what it is from about three different lists.

I guess it is not as clear cut as it seems. I would have also thought that
with the Quantum training session the other day, we would have our own proj4
definitions sorted out. No?

Andrew

-----Original Message-----
From: [hidden email] [mailto:[hidden email]]
On Behalf Of Jeff McKenna
Sent: 21 July 2009 02:08 PM
To: Africa local chapter discussions
Subject: Re: [OSGeo Africa] EPSG 205x

Andrew de Klerk wrote:

> Hi
>
>
>
> Can anyone confirm what the correct Proj4 definition is for our
> Hartebeesthoek projections. The closest I have come up with is (for 2054):
>
> +proj=tmerc +ellips=WGS84 +datum=WGS84 +lon_0=31 +k_0=1 +units=m +no_defs
>
>
>
> I have tried on numerous occasions to get someone in the know to say if
> its wrong or right. I do not know enough about the inner workings of
> projection systems nor the different options available in the proj4
> definitions - so if anyone who knows more than me about either of these
> can help me/us come up with a definite definition this would help.
>
>
>
> Gavin - I know you were looking into this a while ago? Did you get any
> further?
>
>
>
> Thanks
>
> Andrew

Andrew,

Maybe you should ask this question on the Proj mailing list
(http://lists.maptools.org/mailman/listinfo/proj), I bet that is where
you'll find help.

-jeff

--
Jeff McKenna
FOSS4G Consulting and Training Services
http://www.gatewaygeomatics.com/

_______________________________________________
Africa mailing list
[hidden email]
http://lists.osgeo.org/mailman/listinfo/africa
Checked by AVG - www.avg.com
Version: 8.5.392 / Virus Database: 270.13.17/2242 - Release Date: 07/20/09
18:29:00

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--
This message is subject to the CSIR's copyright terms and conditions, e-mail
legal notice, and implemented Open Document Format (ODF) standard.
The full disclaimer details can be found at
http://www.csir.co.za/disclaimer.html.

This message has been scanned for viruses and dangerous content by
MailScanner,
and is believed to be clean. MailScanner thanks Transtec Computers for
their support.

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legal notice, and implemented Open Document Format (ODF) standard.
The full disclaimer details can be found at
http://www.csir.co.za/disclaimer.html.

This message has been scanned for viruses and dangerous content by
MailScanner,
and is believed to be clean. MailScanner thanks Transtec Computers for
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Jeff McKenna

Re: EPSG 205x

Reply Threaded

Andrew de Klerk wrote:
> So the long and the short of it is we cannot use the FOSS tools to their
> full potential until the proj library has been updated to accommodate our
> projection systems. Is that correct?
>

Andrew,

I have personally assisted 2 different groups in Canada that were
complaining of the same issue. The good news is that all it takes is
someone to 'champion' this: by filing a request to have your projection
added (or modified) in the EPSG standard:
http://www.epsg.org/Comms/Comment.asp

That's all it takes. So please feel free to take on that role for your
problem projection, and your work will be helpful to other users in your
country.

-jeff

--
Jeff McKenna
FOSS4G Consulting and Training Services
http://www.gatewaygeomatics.com/

_______________________________________________
Africa mailing list
[hidden email]
http://lists.osgeo.org/mailman/listinfo/africa

Andrew de Klerk-2

RE: EPSG 205x

Reply Threaded

Thanks jeff - I will do just that!

-----Original Message-----
From: [hidden email] [mailto:[hidden email]]
On Behalf Of Jeff McKenna
Sent: 21 July 2009 06:07 PM
To: Africa local chapter discussions
Subject: Re: [OSGeo Africa] EPSG 205x

Andrew de Klerk wrote:
> So the long and the short of it is we cannot use the FOSS tools to their
> full potential until the proj library has been updated to accommodate our
> projection systems. Is that correct?
>

Andrew,

I have personally assisted 2 different groups in Canada that were
complaining of the same issue. The good news is that all it takes is
someone to 'champion' this: by filing a request to have your projection
added (or modified) in the EPSG standard:
http://www.epsg.org/Comms/Comment.asp

That's all it takes. So please feel free to take on that role for your
problem projection, and your work will be helpful to other users in your
country.

-jeff

--
Jeff McKenna
FOSS4G Consulting and Training Services
http://www.gatewaygeomatics.com/

_______________________________________________
Africa mailing list
[hidden email]
http://lists.osgeo.org/mailman/listinfo/africa
Checked by AVG - www.avg.com
Version: 8.5.392 / Virus Database: 270.13.17/2242 - Release Date: 07/20/09
18:29:00

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Walter Smit

RE: EPSG 205x

Reply Threaded

In reply to this post by graeme mcferren

Hi Andrew,

The problem is that many people in South Africa follow international
practice and use the "LO system" NAME for "normal" Mercator projections (not
south facing). This leads to a LOT of confusion.

This "South African LO" projection has always been stupid in my opinion (and
many other people I know). Just because some surveyor was too lazy to write
long numbers and negative signs many many years ago does not mean we should
use it. I for one never use it and advise other people to rather use the
"correct" version of tmerc.

In other words: your proj4 definition is correct (for normal Mercator
projection) - the south facing LO projection is just wrong. If you really
need to define the upside down LO projection you can just set the scale to
-1 in ESRI products (which I believe run on GDAL/OGR??). Unfortunately this
doesn't seem to work in Quantum. Dammit.

Just my 2 cents (and a little ranting) :-)

Regards
Walter

-----Original Message-----
From: [hidden email] [mailto:[hidden email]]
On Behalf Of Graeme McFerren
Sent: 21 July 2009 04:31 PM
To: 'Africa local chapter discussions'
Subject: RE: [OSGeo Africa] EPSG 205x

Hi Andrew

A bit of clarification on what I said earlier:

SA's LO system is a modified Transverse Mercator (Gauss Conform) in which
your metres South positively increases. To the east of the Central Meridian
your values decrease, while to the west they increase and are positive

So your example outputs would be correct for a standard Transverse Mercator
, but incorrect for the LO system we use

Graeme

>>> "Andrew de Klerk" <[hidden email]> 07/21/09 4:04 PM >>>
Hi Graeme

Thanks for the response. Yes, I am well aware of the resource available
through spatialreference. This is where my confusion comes in. if you run
the following:

cs2cs +proj=latlong +datum=WGS84 +to +proj=tmerc +lon_0=31 +datum=WGS84

and then enter:
30.352 -29.623

You will get:
-62758.77 -3278498.65 0.00

This is of course the correct answer. Which immediately tells me that the
definitions in place can handle our projection systems, and it is merely a
factor of syntax. Please correct me if I am wrong.

Andrew

-----Original Message-----
From: [hidden email] [mailto:[hidden email]]
On Behalf Of Graeme McFerren
Sent: 21 July 2009 03:26 PM
To: 'Africa local chapter discussions'
Subject: RE: [OSGeo Africa] EPSG 205x

Hi Andrew

This question needs a bit of disambiguation (oops, I sound like
wikipedia...) and discussion

I remind you btw of the excellent resource www.spatialreference.org

The Hartebeesthoek94 coord system is EPSG:4148
(http://www.spatialreference.org/ref/epsg/4148/ ) defined in proj format as:
+proj=longlat +ellps=WGS84 +towgs84=0,0,0,0,0,0,0 +no_defs

Projected systems can of course be based on this, but if you are
specifically after the LO flavour of things check out:

http://www.spatialreference.org/ref/epsg/2046/
http://www.spatialreference.org/ref/epsg/2047/
...
http://www.spatialreference.org/ref/epsg/2055/

None of these provide a proj4 definition though, nor can I find one in
PostGIS or via OSR, implying to me that it would be difficult to project
into these projections if using some FOSS Tools.

I don't think your proj4 style attempt will quite work though, because it
does not provide for the necessary southward orientation. LO is a
south-oriented Transverse Mercator AFAIK

When resolved, this should be contributed to SpatialReference.org, I think

Regards
Graeme

>>> "Andrew de Klerk" <[hidden email]> 07/21/09 2:30 PM >>>
Jeff - It has already asked on this list. I am yet to get a conclusive
definition of what it is from about three different lists.

I guess it is not as clear cut as it seems. I would have also thought that
with the Quantum training session the other day, we would have our own proj4
definitions sorted out. No?

Andrew

-----Original Message-----
From: [hidden email] [mailto:[hidden email]]
On Behalf Of Jeff McKenna
Sent: 21 July 2009 02:08 PM
To: Africa local chapter discussions
Subject: Re: [OSGeo Africa] EPSG 205x

Andrew de Klerk wrote:

> Hi
>
>
>
> Can anyone confirm what the correct Proj4 definition is for our
> Hartebeesthoek projections. The closest I have come up with is (for 2054):
>
> +proj=tmerc +ellips=WGS84 +datum=WGS84 +lon_0=31 +k_0=1 +units=m +no_defs
>
>
>
> I have tried on numerous occasions to get someone in the know to say if
> its wrong or right. I do not know enough about the inner workings of
> projection systems nor the different options available in the proj4
> definitions - so if anyone who knows more than me about either of these
> can help me/us come up with a definite definition this would help.
>
>
>
> Gavin - I know you were looking into this a while ago? Did you get any
> further?
>
>
>
> Thanks
>
> Andrew

Andrew,

Maybe you should ask this question on the Proj mailing list
(http://lists.maptools.org/mailman/listinfo/proj), I bet that is where
you'll find help.

-jeff

--
Jeff McKenna
FOSS4G Consulting and Training Services
http://www.gatewaygeomatics.com/

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Andrew de Klerk-2

RE: EPSG 205x

Reply Threaded

Walter

Thanks for your response. That is exactly what I thought, but was getting
side-tracked with all this South orientated jargon. 99% of GIS users use
normal transverse Mercator, while some Engineering firms and surveyors use
this modified (south-orientated) transverse mercator. (and yes ESRI does use
GDAL as far as I am aware). The reason we have done this is because these
GIS products have never supported south orientated transverse mercator

Therefore in essence 99% of users wanting to use FOSS products such as GDAL
could successfully reproject etc just by using the EPSG definition that I am
using below based upon normal transverse mercator.

The big question is that if our projection system is officially south
orientated then would it be correct to include std tmerc in the Proj4
library for 205x? Or do we need to request some new entries to be included
in the EPSG file to handle std tmerc with WGS84 datum and l015 to 33?

Regards
Andrew

-----Original Message-----
From: [hidden email] [mailto:[hidden email]]
On Behalf Of Walter Smit
Sent: 22 July 2009 09:22 AM
To: 'Africa local chapter discussions'
Subject: RE: [OSGeo Africa] EPSG 205x

Hi Andrew,

The problem is that many people in South Africa follow international
practice and use the "LO system" NAME for "normal" Mercator projections (not
south facing). This leads to a LOT of confusion.

This "South African LO" projection has always been stupid in my opinion (and
many other people I know). Just because some surveyor was too lazy to write
long numbers and negative signs many many years ago does not mean we should
use it. I for one never use it and advise other people to rather use the
"correct" version of tmerc.

In other words: your proj4 definition is correct (for normal Mercator
projection) - the south facing LO projection is just wrong. If you really
need to define the upside down LO projection you can just set the scale to
-1 in ESRI products (which I believe run on GDAL/OGR??). Unfortunately this
doesn't seem to work in Quantum. Dammit.

Just my 2 cents (and a little ranting) :-)

Regards
Walter

-----Original Message-----
From: [hidden email] [mailto:[hidden email]]
On Behalf Of Graeme McFerren
Sent: 21 July 2009 04:31 PM
To: 'Africa local chapter discussions'
Subject: RE: [OSGeo Africa] EPSG 205x

Hi Andrew

A bit of clarification on what I said earlier:

SA's LO system is a modified Transverse Mercator (Gauss Conform) in which
your metres South positively increases. To the east of the Central Meridian
your values decrease, while to the west they increase and are positive

So your example outputs would be correct for a standard Transverse Mercator
, but incorrect for the LO system we use

Graeme

>>> "Andrew de Klerk" <[hidden email]> 07/21/09 4:04 PM >>>
Hi Graeme

Thanks for the response. Yes, I am well aware of the resource available
through spatialreference. This is where my confusion comes in. if you run
the following:

cs2cs +proj=latlong +datum=WGS84 +to +proj=tmerc +lon_0=31 +datum=WGS84

and then enter:
30.352 -29.623

You will get:
-62758.77 -3278498.65 0.00

This is of course the correct answer. Which immediately tells me that the
definitions in place can handle our projection systems, and it is merely a
factor of syntax. Please correct me if I am wrong.

Andrew

-----Original Message-----
From: [hidden email] [mailto:[hidden email]]
On Behalf Of Graeme McFerren
Sent: 21 July 2009 03:26 PM
To: 'Africa local chapter discussions'
Subject: RE: [OSGeo Africa] EPSG 205x

Hi Andrew

This question needs a bit of disambiguation (oops, I sound like
wikipedia...) and discussion

I remind you btw of the excellent resource www.spatialreference.org

The Hartebeesthoek94 coord system is EPSG:4148
(http://www.spatialreference.org/ref/epsg/4148/ ) defined in proj format as:
+proj=longlat +ellps=WGS84 +towgs84=0,0,0,0,0,0,0 +no_defs

Projected systems can of course be based on this, but if you are
specifically after the LO flavour of things check out:

http://www.spatialreference.org/ref/epsg/2046/
http://www.spatialreference.org/ref/epsg/2047/
...
http://www.spatialreference.org/ref/epsg/2055/

None of these provide a proj4 definition though, nor can I find one in
PostGIS or via OSR, implying to me that it would be difficult to project
into these projections if using some FOSS Tools.

I don't think your proj4 style attempt will quite work though, because it
does not provide for the necessary southward orientation. LO is a
south-oriented Transverse Mercator AFAIK

When resolved, this should be contributed to SpatialReference.org, I think

Regards
Graeme

>>> "Andrew de Klerk" <[hidden email]> 07/21/09 2:30 PM >>>
Jeff - It has already asked on this list. I am yet to get a conclusive
definition of what it is from about three different lists.

I guess it is not as clear cut as it seems. I would have also thought that
with the Quantum training session the other day, we would have our own proj4
definitions sorted out. No?

Andrew

-----Original Message-----
From: [hidden email] [mailto:[hidden email]]
On Behalf Of Jeff McKenna
Sent: 21 July 2009 02:08 PM
To: Africa local chapter discussions
Subject: Re: [OSGeo Africa] EPSG 205x

Andrew de Klerk wrote:

> Hi
>
>
>
> Can anyone confirm what the correct Proj4 definition is for our
> Hartebeesthoek projections. The closest I have come up with is (for 2054):
>
> +proj=tmerc +ellips=WGS84 +datum=WGS84 +lon_0=31 +k_0=1 +units=m +no_defs
>
>
>
> I have tried on numerous occasions to get someone in the know to say if
> its wrong or right. I do not know enough about the inner workings of
> projection systems nor the different options available in the proj4
> definitions - so if anyone who knows more than me about either of these
> can help me/us come up with a definite definition this would help.
>
>
>
> Gavin - I know you were looking into this a while ago? Did you get any
> further?
>
>
>
> Thanks
>
> Andrew

Andrew,

Maybe you should ask this question on the Proj mailing list
(http://lists.maptools.org/mailman/listinfo/proj), I bet that is where
you'll find help.

-jeff

--
Jeff McKenna
FOSS4G Consulting and Training Services
http://www.gatewaygeomatics.com/

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