On Oct 13, 2009, at 3:51 AM, [email protected] wrote:
Date: Tue, 13 Oct 2009 02:18:32 -0700 (PDT)
From: Hamish <[email protected]>
Subject: Re: [GRASS-dev] problems with datum parameters tables
To: list GRASS developers <[email protected]>, Michael Barton
<[email protected]>
Message-ID: <[email protected]>
Content-Type: text/plain; charset=utf-8
Michael Barton wrote:
I'm working on the GUI location
manager and have run into a couple of irregularities in a
couple of the projections parameters files. I'm sending this
to the list instead of keeping it in the location wizard
track ticket because they are a more general issue that will
affect projection/location creation by other means too.
In proj-parms.table, the entry for "GEOS" is incorrect.
There should be 3 subentries for each entry: projection
code, projection description, and required parameters.
However, GEOS is missing the projection description.
GEOS:HEIGH=ask,35800000.0;LON0=ask,20.0
The following entry has the correct format
GINS8:Ginsburg VIII (TsNIIGAiK):LAT0=ask,0.0;LON0=ask,20.0
GEOS is the only incorrect formatted entry in the file.
That's the view-from-a-geostationary-satellite projection. (e.g.
Google
Earth app zoomed way out from space) I guess the missing name is a
typo.
http://www.remotesensing.org/geotiff/proj_list/geos.html
Need to add this so that we can use it. If it has the wrong number of
parameters it won't be parsed correctly.
It's a really neat one to reproject world wide datasets into.
View of the Earth/Mars/Moon from space from any angle and any
distance.
FWIW at those distances 100m offset from a datum probably ain't much
to
worry about.
Sounds cool.
It also is NOT in the datums.table file.
It shouldn't be. Generally speaking, projections and datums are
completely
independent animals and can be mixed at will. Popular convention
means that
in practice some datums are always used with some projections, but
that's
not to satisfy the math, just history.
I doubt any of the proj-*.table entries will be found in the
datum.table
file, except perhaps as a footnote comment.
I meant to say that it is not in the projections file, not the
datum.table file. But this brings up a related issue. Except for the
missing GEOS projection, it looks to me like all the information in
the projections file is also contained in the proj-parms.table file.
So it seems like we should be parsing the latter rather than the
former for getting projections. What is the point of the projections
file anyway if all the same stuff is in the proj-parms.table file?
One difference is that projection codes are in caps in proj-
parms.table and in lower case in the projections file. Does this make
any difference when making a PROJ4 string?
Also, in the proj-desc.table, several entries are
incorrectly formatted. None of them are used by the
proj-parms.table and so they probably should be removed from
the proj-desc.table file.
IMO fixing is better than removing..
All are missing their description fields that are needed so that they
can be read by a user.
I'm guessing the missing descriptions are due to lack of explanation
of what they do by the person who made the table.
They are:
GUAM:bool:guam:
OALPHA:lat:o_alpha:
OLAT1:lat:o_lat_1:
OLAT2:lat:o_lat_2:
OLON1:lon:o_lon_1:
OLON2:lon:o_lon_2:
OLONC:lon:o_lon_c:
the format looks ok as far as having the correct number of
delimiters, the
only issue is that the description is an empty string. Parsing
should be
made to deal with that, but descriptions should be found too.
These terms are not unique to GRASS btw, they come from PROJ.4 or
prior.
+guam has been around for a long while, you probably have to dig into
the PROJ source code to see what they do exactly (or ask Gerald E).
I've tried to document as many as I know about here:
https://trac.osgeo.org/proj/wiki/GenParms
We will need the human readable description if we ever want to use
these parameters. The description is what is presented to the user in
order to get him/her to input a value.
Hamish
ps- lest it be forgot, FYI currently we are completely ignoring
GRASS's
built-in State Plane support; currently those are only available via
the
EPSG files and user knowing+entering custom +proj4 terms.
??? It is in the projections file and hence in the list of projections
to choose from in the current location wizard.
Michael
_______________________________________________
grass-dev mailing list
[email protected]
http://lists.osgeo.org/mailman/listinfo/grass-dev
