Details Ticket 4877


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Serial Number 4877
Subject d.grid -g, ps.map: incorrect geogrid rendering
Area grass6
Queue grass
Requestors hamish_nospam@yahoo.com
Owner none
Status resolved
Last User Contact Wed Jul 19 16:13:51 2006 (2 yr ago)
Current Priority 50
Final Priority 70
Due No date assigned
Last Action Tue Jul 25 12:57:27 2006 (2 yr ago)
Created Wed Jul 19 09:28:20 2006 (2 yr ago)

Transaction History Ticket 4877


Wed, Jul 19 2006 09:28:20    Request created by hbowman  
Subject: d.grid -g, ps.map: incorrect geogrid rendering

Hi,

"d.grid -g" and ps.map's geogrid command are not calculating the correct grid
lines for me. (lines are drawn 90m to the north)

Perhaps it is only doing the projection, and not the datum transform ?!!?

Lon is *exactly* correct though, only lat is just slightly 3" to the north. Weird.
"d.where -w" gets it correct. Also tested with a v.mkproj in LL location +
v.proj into projected location. So I am pretty happy the data is ok just the
grid lines are drawn wrong.

Happens with both NTv2 grid and 7-term transform parms,
proj=nzmg
datum=nzgd49



?
Hamish
Wed, Jul 19 2006 11:01:28    Mail sent by paul-grass@stjohnspoint.co.uk  
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Subject Re: [GRASS-dev] [bug #4877] (grass) d.grid -g, ps.map: incorrect geogrid rendering
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Hello Hamish

On Wed, 19 Jul 2006, Request Tracker wrote:

> this bug's URL: http://intevation.de/rt/webrt?serial_num=4877
> -------------------------------------------------------------------------
>
> Subject: d.grid -g, ps.map: incorrect geogrid rendering
>
> Hi,
>
> "d.grid -g" and ps.map's geogrid command are not calculating the correct grid
> lines for me. (lines are drawn 90m to the north)
>
> Perhaps it is only doing the projection, and not the datum transform ?!!?

Looking at the code, this seems quite possible. I have applied a patch in 
CVS - can you test? If it's working now, I expect we should be able to 
apply a similar patch to ps.map.

Slightly more in-depth explanation:
this behaviour stems from a questionable "feature" of PROJ (my words 
really although Frank has agreed too---see PROJ bug 368 
http://bugzilla.remotesensing.org/show_bug.cgi?id=368 ) where if one 
co-ordinate system has datum transformation parameters specified and 
the other does not, a kind of partial transformation is done. IMHO if the 
datum information is not fully specified it should be ignored completely, 
but that is not possible the way the datum information is contained as 
part of the co-ordinate system in PROJ. Thierry Laronde and KerGIS were 
doing this a different way to avoid this problem as far as I remember...

Paul


Wed, Jul 19 2006 11:57:50    Mail sent by hamish_nospam@yahoo.com  
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Date Wed, 19 Jul 2006 21:57:45 +1200
From Hamish <hamish_nospam@yahoo.com>
To Paul Kelly via RT <grass-bugs@intevation.de>
Cc paul-grass@stjohnspoint.co.uk
Subject Re: [bug #4877] (grass) d.grid -g, ps.map: incorrect
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> > this bug's URL: http://intevation.de/rt/webrt?serial_num=4877
> > -------------------------------------------------------------------
..
> > "d.grid -g" and ps.map's geogrid command are not calculating the
> > correct grid lines for me. (lines are drawn 90m to the north)
> >
> > Perhaps it is only doing the projection, and not the datum transform
> > ?!!?
> 
> Looking at the code, this seems quite possible. I have applied a patch
> in  CVS - can you test? If it's working now, I expect we should be
> able to  apply a similar patch to ps.map.

umm, now it is twice as bad. the 'd.grid -g' line is now drawn 180m
north of the expected location.


> Slightly more in-depth explanation:
> this behaviour stems from a questionable "feature" of PROJ (my words 
> really although Frank has agreed too---see PROJ bug 368 
> http://bugzilla.remotesensing.org/show_bug.cgi?id=368 ) where if one 
> co-ordinate system has datum transformation parameters specified and 
> the other does not, a kind of partial transformation is done. IMHO if
> the  datum information is not fully specified it should be ignored
> completely,  but that is not possible the way the datum information is
> contained as  part of the co-ordinate system in PROJ. Thierry Laronde
> and KerGIS were  doing this a different way to avoid this problem as
> far as I remember...

I take it that in this case the LL datum was the one missing?

#rendering location
G61 > g.proj -p
-PROJ_INFO-------------------------------------------------
name       : New Zealand Map Grid
datum      : nzgd49
nadgrids   : nzgd2kgrid0005.gsb
proj       : nzmg
ellps      : international
a          : 6378388.0000000000
es         : 0.0067226700
f          : 297.0000000000
lat_0      : -41.0000000000
lon_0      : 173.0000000000
x_0        : 2510000.0000000000
y_0        : 6023150.0000000000
-PROJ_UNITS------------------------------------------------
unit       : meter
units      : meters
meters     : 1.0



Hamish


Wed, Jul 19 2006 13:16:41    Mail sent by paul-grass@stjohnspoint.co.uk  
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Subject Re: [bug #4877] (grass) d.grid -g, ps.map: incorrect
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On Wed, 19 Jul 2006, Hamish wrote:

>>> this bug's URL: http://intevation.de/rt/webrt?serial_num=4877
>>> -------------------------------------------------------------------
> ..
>>> "d.grid -g" and ps.map's geogrid command are not calculating the
>>> correct grid lines for me. (lines are drawn 90m to the north)
>>>
>>> Perhaps it is only doing the projection, and not the datum transform
>>> ?!!?
>>
>> Looking at the code, this seems quite possible. I have applied a patch
>> in  CVS - can you test? If it's working now, I expect we should be
>> able to  apply a similar patch to ps.map.
>
> umm, now it is twice as bad. the 'd.grid -g' line is now drawn 180m
> north of the expected location.

For me (I've tried with a test NZMG/nzgd49 location) before the patch the 
lines were about 90m *south* of where they'd be expected to be from the 
d.where -l output, and after the patch they agree :/ d.grid is supposed to 
show lines of latitude&longtiude on the current ellipsoid, not WGS84, 
right?

> I take it that in this case the LL datum was the one missing?

Yes the way it was being done was ll was set as the projection and the 
ellipsoid parameters were copied over to the new parameters, but not the 
datum. I've double-checked and am fairly confident that particular problem 
is fixed now, but perhaps there was something else in the code that 
compensated for this bug and so something else needs changed? I'm not sure 
where to look.

Paul


Wed, Jul 19 2006 13:56:21    Mail sent by hamish_nospam@yahoo.com  
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To Paul Kelly <paul-grass@stjohnspoint.co.uk>
Cc grass-bugs@intevation.de, grass-dev@grass.itc.it
Subject Re: [bug #4877] (grass) d.grid -g, ps.map: incorrect
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> >>> this bug's URL: http://intevation.de/rt/webrt?serial_num=4877
> >-------------------------------------------------------------------
> > ..
> >>> "d.grid -g" and ps.map's geogrid command are not calculating the
> >>> correct grid lines for me. (lines are drawn 90m to the north)
..
> > umm, now it is twice as bad. the 'd.grid -g' line is now drawn 180m
> > north of the expected location.
> 
> For me (I've tried with a test NZMG/nzgd49 location) before the patch
> the lines were about 90m *south* of where they'd be expected to be
> from the d.where -l output, and after the patch they agree :/ d.grid
> is supposed to show lines of latitude&longtiude on the current
> ellipsoid, not WGS84, right?

aah, ok, that's it. The nzgd49 datum uses the int'l ellipsoid.

using "d.where -l" I see that "d.grid -g" does in fact lie in the
correct place (after applying your patch).

the rasterized nautical chart I was using as a backdrop is WGS84.
using "d.where -w" the printed rasterized grid lines match up.

I guess d.grid's default should be to use the current ellipsoid; should
d.grid get a -w flag too?


thanks,
Hamish


Wed, Jul 19 2006 16:13:51    Mail sent by paul-grass@stjohnspoint.co.uk  
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Subject Re: [bug #4877] (grass) d.grid -g, ps.map: incorrect
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On Wed, 19 Jul 2006, Hamish wrote:

> the rasterized nautical chart I was using as a backdrop is WGS84.
> using "d.where -w" the printed rasterized grid lines match up.
>
> I guess d.grid's default should be to use the current ellipsoid; should
> d.grid get a -w flag too?

I don't see why not. I have added this functionality to the CVS HEAD 
version, and backported the bugfixes to d.grid and ps.map to the 6.1 
release branch.

Paul


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Subject Re: [bug #4877] (grass) d.grid -g, ps.map: incorrect
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> > the rasterized nautical chart I was using as a backdrop is WGS84.
> > using "d.where -w" the printed rasterized grid lines match up.
> >
> > I guess d.grid's default should be to use the current ellipsoid;
> > should d.grid get a -w flag too?
> 
> I don't see why not. I have added this functionality to the CVS HEAD 
> version, and backported the bugfixes to d.grid and ps.map to the 6.1 
> release branch.


-w works a treat, thanks

Hamish


Tue, Jul 25 2006 12:57:27    Status changed to resolved by pkelly  
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