[GRASS5] Re: GRASS: "default" datum parameters

[Markus Neteler]

Hello Paul,

thanks for your efforts! It's good to know that datum stuff
is no longer scattered around.

Here, for the record, the same test again:

++++++++++++++++++++++++ Gauss Boaga, Italy ++++++++++++
Please specify datum name
Enter 'list' for the list of available datums
or 'custom' if you wish to enter custom parameters
Hit RETURN to cancel request
>rome40

Now select Datum Transformation Parameters
Please think carefully about the area covered by your data
and the accuracy you require before making your selection.

Enter 'list' to see the list of available Parameter sets
Enter the corresponding number, or <RETURN> to cancel request
>list
Number  Details
---
1       Used in Italy (Peninsular Part)
        (PROJ.4 Params towgs84=-104.1,-49.1,-9.9,0.971,-2.917,0.714,-11.68)
        Accuracy 3-4m
---
2       Used in Italy (Sardinia)
        (PROJ.4 Params towgs84=-168.6,-34.0,38.6,-0.374,-0.679,-1.379,-9.48)
        Accuracy 3-4m
---
3       Used in Italy (Sicily)
        (PROJ.4 Params towgs84=-50.2,-50.4,84.8,-0.690,-2.012,0.459,-28.08)
        Accuracy 3-4m
---
4       Used in whole rome40 region
        (PROJ.4 Params towgs84=-225.000,-65.000,9.000)
        Default 3-Parameter Transformation (May not be optimum for older datums; use this only if no mor
e appropriate options are available.)
---

Now select Datum Transformation Parameters
Please think carefully about the area covered by your data
and the accuracy you require before making your selection.

Enter 'list' to see the list of available Parameter sets
Enter the corresponding number, or <RETURN> to cancel request
> 1

++++++++++++++++++++++++ END ++++++++++++++++++++++++

Now the wording should be clear. Of course, the user *has*
to think...

Thanks again

 Markus



On Fri, Mar 31, 2006 at 10:13:53AM +0100, Paul Kelly wrote:
> Hello Markus
> 
> On Thu, 30 Mar 2006, Markus Neteler wrote:
> 
> >---
> >4       Used in Default rome40 region            <<<<<<< Default ??
> >       (PROJ.4 Params towgs84=-225.000,-65.000,9.000)
> >       Default 3-Parameter Transformation       <<<<<<< Default ??
> >---
> >
> >Of course the user has to select, but a newbie always takes the
> >value called "Default" which is the worse of the selections here
> >(even as it is the *Sardegna* 3 params which is not indicated, not
> >peninsula!).
> >
> >Do you have a suggestion to substitute the "Used in Default" message?
> 
> I agree it is definitely a problem. But for some datums like WGS84 then 
> this default value is actually the best and the one they should use. So 
> we can't just change the message to say something like "low accuracy; 
> don't use this one!" as it is not true for all datums. Most of the time 
> however when there is only one option the user will not be prompted. So it 
> is maybe OK!
> 
> I have made some changes in CVS to add an extra informational message and 
> not make the word "default" so prominent. I also tidied up gislib slightly 
> by removing some datum transformation functions that are no longer used.
> 
> Paul