[GRASS-dev] problems with datum parameters tables

GRASS GRASS developer
1

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. It also is NOT in the datums.table file. So either it should be:

1) deleted from proj-parms.table, or
2) added to datums.table and a descriptive field added in proj-parms.table

Because it cannot be correctly parsed, I'll just skip it in the GUI location wizard. But if we are going to use this projection, it needs to be corrected in the 2 tables.

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. All are missing their description fields that are needed so that they can be read by a user. 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:

Michael

2

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

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.

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.

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

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.

3

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

Well caught.

GEOS is the only incorrect formatted entry in the file. It also is NOT
in the datums.table file. So either it should be:

1) deleted from proj-parms.table, or
2) added to datums.table and a descriptive field added in proj-
parms.table

Because it cannot be correctly parsed, I'll just skip it in the GUI
location wizard. But if we are going to use this projection, it needs
to be corrected in the 2 tables.

The history behind that entry:

http://lists.osgeo.org/pipermail/grass-dev/2006-December/028324.html
http://trac.osgeo.org/grass/changeset/22186

IOW, it should probably be there, but should have the right number of
fields (ideally an actual description, but an empty description is
better than invalid syntax).

[I see that this has now been done.]

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. All are
missing their description fields that are needed so that they can be
read by a user. 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:

These are correctly formatted; they just have an empty description.

I removed the data from the g.setproj source code and placed it in
external files. Any descriptions (or lack of them) are as found in the
original g.setproj source code.

If you want to add descriptions, you'll need to examine the PROJ
source code. However, some parameters may have entirely different
meanings for different projections.

--
Glynn Clements <glynn@gclements.plus.com>

4

Thanks much Glynn. This is helpful. There is no urgency on the parameters without descriptions right now since nothing seems to use these, but we can't use them in the future without some kind of description to parse.

Michael

On Oct 14, 2009, at 6:22 AM, Glynn Clements wrote:

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

Well caught.

GEOS is the only incorrect formatted entry in the file. It also is NOT
in the datums.table file. So either it should be:

1) deleted from proj-parms.table, or
2) added to datums.table and a descriptive field added in proj-
parms.table

Because it cannot be correctly parsed, I'll just skip it in the GUI
location wizard. But if we are going to use this projection, it needs
to be corrected in the 2 tables.

The history behind that entry:

[GRASS-dev] Missing projections
Changeset 22186 – GRASS GIS

IOW, it should probably be there, but should have the right number of
fields (ideally an actual description, but an empty description is
better than invalid syntax).

[I see that this has now been done.]

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. All are
missing their description fields that are needed so that they can be
read by a user. 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:

These are correctly formatted; they just have an empty description.

I removed the data from the g.setproj source code and placed it in
external files. Any descriptions (or lack of them) are as found in the
original g.setproj source code.

If you want to add descriptions, you'll need to examine the PROJ
source code. However, some parameters may have entirely different
meanings for different projections.

--
Glynn Clements <glynn@gclements.plus.com>