Running the cities example in the pdf documents gives different results

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Running the cities example in the pdf documents gives different results

Dean Schulze

I ran the cities example using the inputs on pg. 4 of the docs at ftp://ftp.remotesensing.org/proj/OF90-284.pdf, but I got different results than shown.  Here are the results I got:

$ proj +proj=poly -r cities.lat.lon.txt
# coordinates for a few cities
-4887445.45 7318110.56 Boston, United States
-5542376.59 6982834.25 New York, United States
171219.46 5415571.82 Paris, France
485343.33 5730932.66’w London, England


The document linked above shows this:

$ proj +proj=poly -r cities
# coordinates for a few cities
-4887590.49 7317961.48 Boston, United States
-5542524.55 6982689.05 New York, United States
171224.94 5415352.81 Paris, France
-8101.66 5707500.23 London, England


Am I doing something wrong, or did something change from when the document was written?

Thanks.
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Re: Running the cities example in the pdf documents gives different results

Martin Desruisseaux-3
Hello Dean

From the peanuts gallery (I'm not familiar about this document and about
Proj.4 changes), the differences that you are observing (except for
London) are of the order of magnitude that I would expect for datum
shifts. For example NAD27 to NAD83 datum shift can be close to 80
metres. I remember that some older Proj.4 versions did not applied any
datum shift unless explicitly instructed to. Newer Proj.4 versions apply
automatically a datum shift, but I do not know which one.

For example in EPSG database 8.9, there is 85 different datum shifts
from NAD27 to WGS84 and 57 different datum shifts from NAD83 to WGS84 -
not even considering newer NAD23 realizations like NAD83(86),
NAD83(2007), NAD83(2011), etc. The datum shift to use depends on the
geographic area of interest (e.g. the values are different for Canada
than for USA). I do not know if there is a way for having Proj.4 to tell
us which datum shift parameters it selected. If the selection algorithm
evolutes, I guess it could be one possible reason for the difference
that you observe.

    Martin


Le 09/05/16 à 15:41, Dean Schulze a écrit :

> I ran the cities example using the inputs on pg. 4 of the docs at ftp://ftp.remotesensing.org/proj/OF90-284.pdf, but I got different results than shown.  Here are the results I got:
>
> $ proj +proj=poly -r cities.lat.lon.txt
> # coordinates for a few cities
> -4887445.45 7318110.56 Boston, United States
> -5542376.59 6982834.25 New York, United States
> 171219.46 5415571.82 Paris, France
> 485343.33 5730932.66’w London, England
>
>
> The document linked above shows this:
>
> $ proj +proj=poly -r cities
> # coordinates for a few cities
> -4887590.49 7317961.48 Boston, United States
> -5542524.55 6982689.05 New York, United States
> 171224.94 5415352.81 Paris, France
> -8101.66 5707500.23 London, England
>
>
> Am I doing something wrong, or did something change from when the document was written?
>
> Thanks.

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Re: Running the cities example in the pdf documents gives different results

José Alberto Gonçalves
In reply to this post by Dean Schulze
Hi
You're not specifying an ellipsoid in the command line. Your PROJ version is using WGS84 by default.
The default ellipsoid of the PROJ version used in the example of the PDF document was Clarke 66.
You get those results with:
proj +proj=poly +ellps=clrk66 -r

Regards

José Gonçalves



2016-05-09 23:41 GMT+01:00 Dean Schulze <[hidden email]>:

I ran the cities example using the inputs on pg. 4 of the docs at ftp://ftp.remotesensing.org/proj/OF90-284.pdf, but I got different results than shown.  Here are the results I got:

$ proj +proj=poly -r cities.lat.lon.txt
# coordinates for a few cities
-4887445.45     7318110.56 Boston, United States
-5542376.59     6982834.25 New York, United States
171219.46       5415571.82 Paris, France
485343.33       5730932.66’w London, England


The document linked above shows this:

$ proj +proj=poly -r cities
# coordinates for a few cities
-4887590.49 7317961.48 Boston, United States
-5542524.55 6982689.05 New York, United States
171224.94 5415352.81 Paris, France
-8101.66 5707500.23 London, England


Am I doing something wrong, or did something change from when the document was written?

Thanks.
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Re: Running the cities example in the pdf documents gives different results

Dean Schulze
Ahhh, so the default ellipsoid changed from the time of writing.

Adding +ellps=clrk66 gives the same results as in the document for the first 3 cities, but the 4th city (London) is way off.  Here's my results:

  $ proj +proj=poly +ellps=clrk66 -r cities.lat.lon.txt
  # coordinates for a few cities
  -4887590.49 7317961.48 Boston, United States
  -5542524.55 6982689.05 New York, United States
  171224.94 5415352.81 Paris, France
  485359.70 5730714.96’w London, England


The document shows the following for London:

-8101.66 5707500.23 London, England

so something else is wrong.  I'm using Rel. 4.8.0, 6 March 2012.


________________________________________
From: [hidden email] [[hidden email]] on behalf of Jose Gonçalves [[hidden email]]
Sent: Tuesday, May 10, 2016 2:19 AM
To: PROJ.4 and general Projections Discussions
Subject: Re: [Proj] Running the cities example in the pdf documents gives different results

Hi
You're not specifying an ellipsoid in the command line. Your PROJ version is using WGS84 by default.
The default ellipsoid of the PROJ version used in the example of the PDF document was Clarke 66.
You get those results with:
proj +proj=poly +ellps=clrk66 -r

Regards

José Gonçalves




2016-05-09 23:41 GMT+01:00 Dean Schulze <[hidden email]<mailto:[hidden email]>>:

I ran the cities example using the inputs on pg. 4 of the docs at ftp://ftp.remotesensing.org/proj/OF90-284.pdf, but I got different results than shown.  Here are the results I got:

$ proj +proj=poly -r cities.lat.lon.txt
# coordinates for a few cities
-4887445.45     7318110.56 Boston, United States
-5542376.59     6982834.25 New York, United States
171219.46       5415571.82 Paris, France
485343.33       5730932.66’w London, England


The document linked above shows this:

$ proj +proj=poly -r cities
# coordinates for a few cities
-4887590.49 7317961.48 Boston, United States
-5542524.55 6982689.05 New York, United States
171224.94 5415352.81 Paris, France
-8101.66 5707500.23 London, England


Am I doing something wrong, or did something change from when the document was written?

Thanks.
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Re: Running the cities example in the pdf documents gives different results

José Alberto Gonçalves
The problem is with the longitude, which is 7 minutes west. If you do the inverse projection with the projected coordinates, you get exactly 7 degrees east.

echo 485359.70 5730714.96 | proj -I +ellps=clrk66 +proj=poly
7dE     51d30'N

The symbol of minutes (') and the w are not being read correctly.

Regards

José




2016-05-10 15:45 GMT+01:00 Dean Schulze <[hidden email]>:
Ahhh, so the default ellipsoid changed from the time of writing.

Adding +ellps=clrk66 gives the same results as in the document for the first 3 cities, but the 4th city (London) is way off.  Here's my results:

  $ proj +proj=poly +ellps=clrk66 -r cities.lat.lon.txt
  # coordinates for a few cities
  -4887590.49   7317961.48 Boston, United States
  -5542524.55   6982689.05 New York, United States
  171224.94     5415352.81 Paris, France
  485359.70     5730714.96’w London, England


The document shows the following for London:

-8101.66 5707500.23 London, England

so something else is wrong.  I'm using Rel. 4.8.0, 6 March 2012.


________________________________________
From: [hidden email] [[hidden email]] on behalf of Jose Gonçalves [[hidden email]]
Sent: Tuesday, May 10, 2016 2:19 AM
To: PROJ.4 and general Projections Discussions
Subject: Re: [Proj] Running the cities example in the pdf documents gives different results

Hi
You're not specifying an ellipsoid in the command line. Your PROJ version is using WGS84 by default.
The default ellipsoid of the PROJ version used in the example of the PDF document was Clarke 66.
You get those results with:
proj +proj=poly +ellps=clrk66 -r

Regards

José Gonçalves




2016-05-09 23:41 GMT+01:00 Dean Schulze <[hidden email]<mailto:[hidden email]>>:

I ran the cities example using the inputs on pg. 4 of the docs at ftp://ftp.remotesensing.org/proj/OF90-284.pdf, but I got different results than shown.  Here are the results I got:

$ proj +proj=poly -r cities.lat.lon.txt
# coordinates for a few cities
-4887445.45     7318110.56 Boston, United States
-5542376.59     6982834.25 New York, United States
171219.46       5415571.82 Paris, France
485343.33       5730932.66’w London, England


The document linked above shows this:

$ proj +proj=poly -r cities
# coordinates for a few cities
-4887590.49 7317961.48 Boston, United States
-5542524.55 6982689.05 New York, United States
171224.94 5415352.81 Paris, France
-8101.66 5707500.23 London, England


Am I doing something wrong, or did something change from when the document was written?

Thanks.
_______________________________________________
Proj mailing list
[hidden email]<mailto:[hidden email]>
http://lists.maptools.org/mailman/listinfo/proj
_______________________________________________
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