From IOSN-InWent FOSS GIS & Sahana Training

Introduction

GRASS (Geographic Resources Analysis Support System,http://www.grass-gis.org) is a free, open source Geographical information system (GIS) capable of handling raster, topological vector, image processing, and graphic data.

There were 3 methods to make GRASS Database:

Using geo-referenced files
Using EPSG
Using projection info

All of those 3 methods will produce spatial information that needed to create GRASS Database:

Coordinate System
Map Projection
Resolution
Boundary

Starting GRASS

Start your GRASS using terminal:

$> grass

Set your GRASS database (it's a directory) to our training convention:

Using EPSG Method

Press the "EPSG Codes" button.
Set new location name ("mentawai_1") and click "Browse" button.
Define your location (depend on your map location, for example we're using 32747).
We can get the ESPG code from:
1. You can use search feature to find the EPSG code. Then click "Grab Code" button.
2. You can use qGIS, open your map and the access menu: Settings > Project Properties > Projection
3. You also can use http://www.epsg-registry.org
Press "Define Location" button.
There'll be a warning window, but's that's OK (normal). We'll asked to restart our GRASS.
Re-open GRASS from terminal:
$> grass
Select project location that we created ("mentawai_1"), that location only have 1 mapset ("PERMANENT"), now we need to add new mapset for our working mapset. Fill the "Create new mapset from selected location" form entry with some name (we'll use our Ubuntu username for this: "fossgis" or "instruktur"). Press the "Create New Mapset" button.
To start our new GRASS session, select our location ("mentawai_1") and select our mapset ("fossgis" or "instruktur"), press "Enter GRASS" button.

Using Projection Values Method

Click "Projection Values" button.
Grass will switch to terminal/console mode with some text based wizard
Create new location by filling "mentawai_2" to LOCATION, hits ESC+RETURN
Would you like to create location <mentawai_2> ? (y/n) [y], hits RETURN
Next step we'll asked if we have information about some information. To get those information we can use this commandline from our converted raster image:
$> gdalinfo /home/USERNAME/maps/raster/srtm/SRTM_MENTAWAI_UTM.tif
Coordinate System? UTM, hits C then RETURN
One line description? "Mentawai UTM Zone 47 South", hits RETURN
Enter geodetic datum? yes, hits RETURN
Please specify datum name? type "wgs84" then hits RETURN
Datum Transformation Parameters? type "1" then hits RETURN
Enter Zone? type "47" then hits RETURN
Is this South Hemisphere? yes, hits RETURN
Then fills the entry region form using coordinates that we can grabbed from gdalinfo.
Corner Coordinates:
Upper Left ( 529311.716, 9818459.444) ( 99d15'48.68"E, 1d38'32.76"S)
Lower Left ( 529311.716, 9564913.077) ( 99d15'50.53"E, 3d56'10.55"S)
Upper Right ( 815918.631, 9818459.444) (101d50'20.65"E, 1d38'25.52"S)
Lower Right ( 815918.631, 9564913.077) (101d50'40.44"E, 3d55'53.18"S)
Center ( 672615.174, 9691686.261) (100d33'10.39"E, 2d47'18.09"S)

Means like this in display:

So, our entries will be:
North: 9818459.444
South: 9564913.077
East: 815918.631
West: 529311.716
hits ESC+RETURN
Then fills the grid resolution form using another information that we grabbed from gdalinfo:
Pixel Size = (30.811321746802712,-30.811321746802712)
So, our entries will be:
East-West: 30.8113217
North-South: 30.8113217
hits ESC+RETURN
We'l asked to review the information, select y then hits ESC+RETURN
Press CTRL+C to quit from the GRASS terminal
Re-open GRASS from terminal:
$> grass
Select project location that we created ("mentawai_2"), that location only have 1 mapset ("PERMANENT"), now we need to add new mapset for our working mapset. Fill the "Create new mapset from selected location" form entry with some name (we'll use our Ubuntu username for this: "fossgis" or "instruktur"). Press the "Create New Mapset" button.
To start our new GRASS session, select our location ("mentawai_2") and select our mapset ("fossgis" or "instruktur"), press "Enter GRASS" button.