[GRASS-user] Low map display resolution in default 6.4 ?

[Felix Schalck]

Dear Nikos,

Many thanks for your reply. But even before listing up the requested
data, please noticed that, basically, I didn't change any settings
(g.region) when upgrading to 6.4: I just compiled and installed the
new version, and now everthing I loaded in 6.23 looks "soappy" in 6.4.
Resolution is important for both live display in GRASS, to control
data elevation errors, and further processing, since the final pgn map
should be exported at the highest possible resolution.

As of the requested additionnal data, here you go:

1. DEM resolution:
$gdalinfo srtm_38_03.tif

Driver: GTiff/GeoTIFF
Files: srtm_38_03.tif
Size is 6000, 6000
Coordinate System is:
GEOGCS["WGS 84",
    DATUM["WGS_1984",
        SPHEROID["WGS 84",6378137,298.2572235630016,
            AUTHORITY["EPSG","7030"]],
        AUTHORITY["EPSG","6326"]],
    PRIMEM["Greenwich",0],
    UNIT["degree",0.0174532925199433],
    AUTHORITY["EPSG","4326"]]
Origin = (5.000000000000000,50.000000000000000)
Pixel Size = (0.000833333333333,-0.000833333333333)
Metadata:
  AREA_OR_POINT=Area
Image Structure Metadata:
  INTERLEAVE=BAND
Corner Coordinates:
Upper Left  (   5.0000000,  50.0000000) (  5d 0'0.00"E, 50d 0'0.00"N)
Lower Left  (   5.0000000,  45.0000000) (  5d 0'0.00"E, 45d 0'0.00"N)
Upper Right (  10.0000000,  50.0000000) ( 10d 0'0.00"E, 50d 0'0.00"N)
Lower Right (  10.0000000,  45.0000000) ( 10d 0'0.00"E, 45d 0'0.00"N)
Center      (   7.5000000,  47.5000000) (  7d30'0.00"E, 47d30'0.00"N)
Band 1 Block=6000x1 Type=Int16, ColorInterp=Gray
  NoData Value=-32768

2. Region settings:
$g.region -p

projection: 3 (Latitude-Longitude)
zone:       0
datum:      wgs84
ellipsoid:  wgs84
north:      60N
south:      34N
west:       11W
east:       35E
nsres:      0:00:03
ewres:      0:00:03
rows:       31200
cols:       55200
cells:      1722240000

If I interpret those numbers correctly, the region is set to the
theoretical max. resolution. Again, since I basically did not touch
the configs during the upgrade procedure (GRASS 6.23>6.4RC5) I thought
to myself it might just be a configuration change of the default
driver used by d.rast: in the old version, it took forever to load,
but the level of details SEEMED much higher, now it loads quasi
instantly, but looks 'soappy'. What changed ?

Regards,

Felix

2009/8/14 Nikos Alexandris <nikos.alexandris at felis.uni-freiburg.de>:
> Felix Schalck:
>> Since I compiled latest 6.4RC5 Grass version, I experienced
>> significative speed gain when displaying DEM raster levels - at the
>> expense of the displayed resolution: the whole thing just looks
>> "soappy", and keeps getting worse once you zoom in. With my previous
>> version (6.23), the same raster display opreration (d.rast) took
>> forever, but I had the possibility to control data errors at the
>> finest level. So surely there must be an option I don't know yet to
>> increase the resolution of the Map display windows; it would be very
>> nice if somebody could explain me how it works.
>
> Hi Felix!
>
> What is the resolution of your DEM?
> Did you set it using "g.region"?
> Are you interested in (only) displaying or (in addition in) processing
> your DEM at high-resolution?
>
> .
>
> If you are new in GRASS-GIS then its worthy to read the intro(s) [1][2].
> Perhaps you are looking info on how to set the resolution which is done
> with the module "g.region"[3]. ( Note that "g.region" != "r.region" )
>
> Apologies if you are familiar with all this, Nikos
> ---
>
> [1] http://grass.osgeo.org/grass64/manuals/html64_user/helptext.html
> [2] http://grass.osgeo.org/grass64/manuals/html64_user/rasterintro.html
> [3] http://grass.osgeo.org/grass64/manuals/html64_user/g.region.html
>
>