[GRASS5] ps.map symbol size from DB column

Radim Blazek radim.blazek at gmail.com
Tue Sep 6 08:51:18 EDT 2005


See v.to.rast, it is necessary to select all cat/value
pairs in one query (otherwise it is slow).  

db_select_CatValArray()
db_CatValArray_get_value_int() / db_CatValArray_get_value_double()

Radim

On 9/6/05, Hamish <hamish_nospam at yahoo.com> wrote:
> Hi,
> 
> 
> I have done most of the code for getting ps.map to do dynamic symbol/eps
> sizing from a DB column, following the d.vect.chart interface. The
> sizing part and variable passing is all complete (currently scaling ok
> from cat number), but I need two things:
> 
> 
> (1) I would like to check that the sizing column name exists and is of a
> numerical type.
> 
> We have Vect_get_column_names_types(Map, layer) in
> lib/vector/Vlib/dbcolumns.c which returns a list of column names and
> types. It would be great to have another fn in dbcolumns.c like
> 
> Vect_column_name_is_type(struct Map_info *Map, int field, char *col_name);
> 
> returning the type or NULL if the column doesn't exist.
> 
> This seems like a useful thing to have, and I think it would be pretty
> simple to do (just parse the output of Vect_get_column_names_types() ).
> 
> Maybe if something is wrong then the vector/db library fn's already give
> a good error message so there is no need to test?
> 
> Maybe this already exists?
> 
> 
> 
> (2) I want to do something like:
> 
> symbol_size = Vect_db_read(Map, layer, column_name, cat);
> 
> to query the value for that category-column combination. How?
> 
> (maybe with an atof() or sscanf("%lf",) step if it returns a string; or
> perhaps multiple fn's like Vect_db_read_dbl() and Vect_db_read_str() ??)
> 
> 
> 
> Preferably the fn's asked for in (1) and (2) should both be abstracted to
> the point where one shouldn't need to be opening DB drivers, etc.
> 
> 
> ????
> sorry, I don't know the DB stuff very well.
> 
> 
> 
> thanks,
> Hamish
> 
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