[GRASS-dev] RE: [GRASS-user] MASK seems to be ignored

[Patton, Eric]

>> Checking the range of the raster I used for a mask in my
>> r.mask command, it was 0-32767; so shouldn't r.mask in=MAP also create a mask 
>> where any non-null cell in the input raster exists?
>> 
>> Here's the output from r.info for the mask I created using r.mask:

>MASK maps usually look like this. It would be more useful to see the
>r.info output for the original map.

r.info output for original map from which the mask was created:

$ r.info Diff_Nov2007_Oct2007_1m
 +----------------------------------------------------------------------------+
 | Layer:    Diff_Nov2007_Oct2007_1m        Date: Mon Feb  4 14:10:04 2008    |
 | Mapset:   PERMANENT                      Login of Creator: epatton         |
 | Location: Charlottetown                                                    |
 | DataBase: /home/epatton/Projects                                           |
 | Title:     ( Diff_Nov2007_Oct2007_1m )                                     |
 | Timestamp: none                                                            |
 |----------------------------------------------------------------------------|
 |                                                                            |
 |   Type of Map:  raster               Number of Categories: 255             |
 |   Data Type:    FCELL                                                      |
 |   Rows:         1136                                                       |
 |   Columns:      1249                                                       |
 |   Total Cells:  1418864                                                    |
 |        Projection: UTM (zone 20)                                           |
 |            N:    5119638    S:    5118502   Res:     1                     |
 |            E:     491292    W:     490043   Res:     1                     |
 |   Range of data:    min = -2.809999  max = 1.246000                        |
 |                                                                            |
 |   Data Description:                                                        |
 |    generated by r.mapcalc                                                  |
 |                                                                            |
 |   Comments:                                                                |
 |    EC_Charlottetown_Bathy_November_2007_1m_fill -                          |
 |    EC_Charlottetown_Bathy_October_2007_1m                                  |
 |                                                                            |
 +----------------------------------------------------------------------------+


>I'm assuming that the original does contain nulls (otherwise the
>r.mapcalc method wouldn't do anything either). Is the original map a
>reclass map?

Yes, the original contains nulls. The original map is not a reclass, but the cell
values do cross through zero, if that matters.

>The r.mapcalc method creates a completely new map, while r.mask
>creates a reclass map. A reclass map takes much less space, but is
>affected by any changes to the underlying map (which can be good or
>bad, depending upon what you want), and may be susceptible to a
>different set of bugs, quirks and corner cases than a normal
>(non-reclass) map.

Good to know; I'll use the r.mapcalc method as it seems a bit more immune to 
strangeness. I'll add some hints about this in the r.mask docs, too.

~ Eric.