[Proj] Some need for updated proj-4 manuals

Gerald I. Evenden geraldi.evenden at gmail.com
Mon Sep 15 11:24:52 EDT 2008

On Sunday 14 September 2008 11:34:06 pm Hamish wrote:
> Janne wrote:
> > Actually the minimium would be to have a list of available projections,
> $ proj -l
> > maybe some picture how it looks
> http://www.galleryofmapprojections.com/  ->
> http://www.csiss.org/map-projections/    (server down?)

I can't get the above to work.

The libproj4 manual has pictures of most of the projections.

> > and an accurate description of all parameters
> I wouldn't guarantee that it's a full set, but these are the ones used
> in the EPSG file.

I am sorry but I find the following meaningless beside very misleading.

> $ cat epsg | grep -v '^#' | tr ' ' '\n' | grep '^\+' | \
>   cut -f1 -d'=' | sort | uniq
> +a
only applies to elliptical projections
What about +R and +R_V, +R_a, +R_g +R_h, +R_lat_a
> +alpha
use limited to 3 or 4 projections and possibly in different contexts
> +b
only one method besides +rf, +f, +e, +es
> +datum
not a proj option
> +ellps
> +k
> +k_0
> +lat_0
> +lat_1
> +lat_2
only for conics
> +lat_ts
only a few projections
> +lon_0
> +lonc
only a couple of projections
> +no_defs
not in libproj4--- nasty option and out of place
> +pm
not in libproj4
> +proj
> +south
only a few projections
> +to_meter
> +towgs84
not in libproj4 --- not projection parameter
> +units
> +x_0
> +y_0
> +zone
only applies to UTM.

If you want a slightly more complete list of about 75 +options try:

a alpha azi b belgium beta czech e ellps es f gamma geoc
guam h k K k_0 lat_0 lat_1 lat_2 lat_b lat_t lat_ts lon_0
lon_1 lon_2 lonc lsat m M n no_cut no_off no_rot ns o_alpha
o_lat_1 o_lat_2 o_lat_c o_lat_p o_lon_1 o_lon_2 o_lon_c
o_lon_p o_proj over p path proj q R R_a R_A rf R_g R_h
R_lat_a R_lat_g rot R_V s south sym t theta tilt to_meter
units vopt W westo x_0 y_0 zone

> > and how they affect the result.

For a discussion of the above options see the libproj4 manual.

> A short sentence/paragraph on each of the above would be nice.

Only the setting of the earth's figure and a couple of the factors like x_0, 
y_0 can be discussed at a generic level.  Most operation need to be discussed 
as part of the projection description---pretty much as now available.

> As Markus suggested, the (FW/OSGeo) proj4 wiki is a nice place to work
> on collaborative documents.
>    http://trac.osgeo.org/proj/wiki/GenParms/

The above is really a web for cs2cs and and only has a smattering of proj 
related material.  Also, I am not sure whether the internals are up to 
libproj4 level.

> I made a start at naming the above, if others could please complete...

The list I made is fairly complete as I grepped it out of the RCS directory.
> There you will find nice things like:
> == Documentation ==
> * General Parameter Notes
> * Projections List page on the GeoTIFF site includes information on how
>   to describe many common projections with PROJ.4 command arguments.
> > The idea behind using libraries is that such work that can
> > be done only once... also would be done only once.

What about updates and upgrades?  That often affect manual contents.

> Right.
> Hamish
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