Hammer projection grid

Hi

I am trying to plot data on the sphere and use the hammer projection.
The data ploting works fine, but the angular grid isn't shown correctly.
In the attached picture you can see the error(mouse pointer is on the
position 60 E 30 S). Can anyone help me on this subject? Thanks.

Matthias

screen.png

Matthias,

Looking at the transform equation for Hammer, it looks like there might be a mistake in the calculation. Can you include the script you used to make that figure so I can test the fix?

Thanks,
Ben Root

···

On Wed, Nov 17, 2010 at 5:45 AM, Matthias Plum <plum@…669…> wrote:

Hi

I am trying to plot data on the sphere and use the hammer projection.

The data ploting works fine, but the angular grid isn’t shown correctly.

In the attached picture you can see the error(mouse pointer is on the

position 60 E 30 S). Can anyone help me on this subject? Thanks.

Matthias

Nevermind about the example script, I tested it myself and verified the problem. The fix was simple. We were missing a square root for the denominator of the formula for x and y. Before I submit this patch, can anybody with more knowledge about the hammer projection verify that the equations on the wikipedia page are correct? I would like to verify the transformation before making this change.

Ben Root

hammer.patch (620 Bytes)

···

On Wed, Nov 17, 2010 at 8:44 AM, Benjamin Root <ben.root@…1304…> wrote:

On Wed, Nov 17, 2010 at 5:45 AM, Matthias Plum <plum@…669…> wrote:

Hi

I am trying to plot data on the sphere and use the hammer projection.

The data ploting works fine, but the angular grid isn’t shown correctly.

In the attached picture you can see the error(mouse pointer is on the

position 60 E 30 S). Can anyone help me on this subject? Thanks.

Matthias

Matthias,

Looking at the transform equation for Hammer, it looks like there might be a mistake in the calculation. Can you include the script you used to make that figure so I can test the fix?

Thanks,
Ben Root

Dear all,

Nevermind about the example script, I tested it myself and verified the
problem. The fix was simple. We were missing a square root for the
denominator of the formula for x and y. Before I submit this patch, can
anybody with more knowledge about the hammer projection verify that the
equations on the wikipedia page are correct? I would like to verify the
transformation before making this change.

The patch seems correct - see

http://www.progonos.com/furuti/MapProj/Dither/CartHow/HowAiHaW3/howAiHaW3.html

or

The Glossary of Mapping Sciences 1994,
http://books.google.com/books?id=jPVxSDzVRP0C&lpg=PA59&ots=n4hOaubxqo&dq=hammer%20projection%20equation&pg=PA241#v=onepage&q&f=true

Best regards,

Tobias

···

On Wednesday 17 November 2010 Benjamin Root wrote:

--
Tobias Winchen
III. Physikalisches Institut A
RWTH Aachen University
+49 (0)241 80 27326

Tobias and Matthias, thanks for the confirmation. I have updated the maintenance branch and the trunk with revisions 8808 and 8809.

Ben Root

···

On Mon, Nov 22, 2010 at 6:59 AM, Tobias Winchen <winchen@…2509…> wrote:

Dear all,

On Wednesday 17 November 2010 Benjamin Root wrote:

Nevermind about the example script, I tested it myself and verified the

problem. The fix was simple. We were missing a square root for the

denominator of the formula for x and y. Before I submit this patch, can

anybody with more knowledge about the hammer projection verify that the

equations on the wikipedia page are correct? I would like to verify the

transformation before making this change.

The patch seems correct - see

http://www.progonos.com/furuti/MapProj/Dither/CartHow/HowAiHaW3/howAiHaW3.html

or

The Glossary of Mapping Sciences 1994,

http://books.google.com/books?id=jPVxSDzVRP0C&lpg=PA59&ots=n4hOaubxqo&dq=hammer%20projection%20equation&pg=PA241#v=onepage&q&f=true

Best regards,

Tobias