On Tuesday 26 November 2002 08:10 pm, Nico Hardebol wrote:
Dear Grass developpers,
With a small group of geological and geophysical master students (Utrecht
University - Geophysica & VU - Amsterdam/ Tectonic depart. under prof. S.
Cloetingh) we are at the moment getting familiar with grass and try to
implement a geotectonic rotation script placed between SQL - requests sent
by grass and a spatial database PostgreSQL - to allow plate tectonic
reconstructions within grass.
We already changed and programmed some lsmall euler-rotation scripts which
rotate tectonic plate shape -polygons. Visualization must be done by GIS -
and to us grass is the best solution - due to the great possibilities of
the gras5.0 release and its future perspectives
Can you explain what the script does with vectors? Transforms coordinates?
Must be done dynamicaly? What is the variable the transformation depends on?
Are there created new objects? Works on geometry only or on attributs?
We have some experience with grass 5.0.0 - we also bought your new book on
open GIS. Your internet site and your article on the new grass5.1
architecture suggests a fully integrated grass with DBMS - PostgreSQL. In
respect to our approach of writing a transformation script this new version
grass5.1 is inportant and the following questions are relevant to us:
1) how is the SQL requesting organized within grass5.1
2) how is the data delivered from the database back to grass5.1 for
visualization.
To get some flexibility, geometry and atributes are handled by separate
libraries.
a) Attributes are read/written through DBMI lib in usual way
similar to other SQL clients, example:
driver = db_start_driver(Fi->driver);
db_set_handle (&handle, Fi->database, NULL);
db_open_database(driver, &handle);
sprintf(buf,"SELECT %s FROM %s WHERE %s\n", col, tab, where);
db_append_string ( &stmt, buf);
db_open_select_cursor(driver, &stmt, &cursor, DB_SEQUENTIAL);
table = db_get_cursor_table (&cursor);
column = db_get_table_column(table, 0); /* first column */
value = db_get_column_value(column);
type = db_get_column_sqltype(column);
type = db_sqltype_to_Ctype(type);
while(1) {
db_fetch (&cursor, DB_NEXT, &more);
if (!more) break;
val = db_get_value_int(value);
}
b) Geometry is read directly from PostGis/Postgress and this is completely
hidden in vector library and can be accessed by Vect_* functions only.
3) Where are we going to put our script within the data-stream.
Why must be in the stream? Cannot work as usual Grass module?
To get familiar with grass5.1 and its linking with postgreSQL I downloaded
and installed the grass5.1 pre-compiled binaries.
Grass5.1 seems to be installed pretty well. Grass5.1 and also the new d.m
starts well (nice display manager). Raster data can be easily plotted but
the vector data (for us the most interesting) offers problems. Pressing
the Vector Name button the sellection window pops up, but no datsets can be
sellected. Is this due to the fact that most modeles from Grass5.0 are
missing and modules to load vector data are absent in the
grass5.1 libraries?
Vector format is changed in 51, so you must first convert vectors from
5.0 to 5.1 by v.convert. The best way to start with g51 is demo mapset
http://mpa.itc.it/radim/g51/g51test-8.tar.gz
unpack, start grass, go to mapset and run 'tour'
from the install notes
" ....Note that most modules from GRASS 5.0 are missing. However, they
can be easily linked into the ./dist.$ARCH structure if needed.
Or, new directories with new Makefiles must be added and the
directory defined in ./tools/link.conf...."
Only that modules from g50 which do not work with vectors or X driver may be
run in grass51. Before you run g50 module you must set some variables
(paths to g50), example:
export PATH=/amd/ssi0/ssi/blazek/grass/dist.i686-pc-linux-gnu/bin:$PATH;
export GISBASE=/amd/ssi0/ssi/blazek/grass/dist.i686-pc-linux-gnu;
How can we load vectore data in grass5.1 via d.m - do we have to link
grass5.0 modules? How?
Via d.m no, it is display manager, use v.convert.
Radim