You can send any comments to Radim Blazek and David D. Gray
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The new format is very similar to old GRASS 4.x (5.0/5.3) vector format.
GRASS vector maps are stored in an arc-node representation, consisting of curves called arcs. An arc is stored as a series of x,y,z coordinate pairs. The two endpoints of an arc are called nodes. Two consecutive x,y,z pairs define an arc segment. The user specifies the type on input to GRASS, GRASS doesn't decide. GRASS allows for the line definition which allows for the multiple type to co-exist in the same map. Centroid are assigned to area it is within/inside (geometrically). An area is identified by an x,y,z centroid point geometrically inside with a category number. This identifies the area. Such centroids are stored in the same binary 'coor' file with other primitives. Each element may have none, one or more categories (cats). More cats are distinguished by field number (field). Single and multi-category support on modules level is implemented. Z-coordinate is optional and both 2d and 3d files may be written.
| Name | Type | Number | Description |
| Version_Major | C | 1 | |
| Version_Minor | C | 1 | |
| Earliest_Major | C | 1 | |
| Earliest_Minor | C | 1 | |
| byte_order | C | 1 | little or big endian flag; files are written in machine native order but files in both little and big endian order may be read |
| with_z | C | 1 | 2D or 3D flag |
| size | L | 1 | coor file size |
| reserved | C | 10 | not used |
| Name | Type | Number | Description |
| record header | I | 1 |
|
| ncats | C | 1 | number of categories (written only if categories exist) |
| field | S | ncats | Category identifier, distinguishes between more categories append to one line (written only if categories exist) |
| cat | I | ncats | category value (written only if categories exist) |
| ncoor | I | 1 | written for GV_LINES and GV_BOUNDARIES only |
| x | D | ncoor | |
| y | D | ncoor | |
| z | D | ncoor | present if with_z in head is set to 1 |
| Type | Name | Size in Bytes |
| D | Double | 8 |
| L | Long | 4 |
| I | Int | 4 |
| S | Short | 4 |
| C | Char | 1 |
ORGANIZATION DIGIT DATE DIGIT NAME MAP NAME MAP DATE MAP SCALE OTHER INFO ZONE MAP THRESH
Topology is written for native format, pseudo-topology is written for PostGRASS, SHAPE-link.
/* Vector types used in memory on run time - may change */ #define GV_POINT 0x01 #define GV_LINE 0x02 #define GV_BOUNDARY 0x04 #define GV_CENTROID 0x08 #define GV_FACE 0x10 #define GV_KERNEL 0x20 #define GV_AREA 0x40Face and kernel are 3D equivalents of boundary and centroid, but there is no support (yet) for 3D topology (volumes). The only current use of face is possibility to display vertical planes in NVIZ.
/* Topology level details */ #define GV_BUILD_NONE 0 #define GV_BUILD_BASE 1 #define GV_BUILD_AREAS 2 #define GV_BUILD_ATTACH_ISLES 3 /* Attach islands to areas */ #define GV_BUILD_CENTROIDS 4 /* Assign centroids to areas */ #define GV_BUILD_ALL GV_BUILD_CENTROIDSGV_BOUNDARY contains geometry and it is used to build areas. GV_LINE cannot form an area.
+--1--+--5--+ | | | 2 A 4 B 6 | | | +--3--+--7--+ 1,2,3,4,5,6,7 = 7 boundaries (primitives) A,B = 2 areas
+---------+ | A | +-----+ | | B | | +-----+ | | | +---------+In GRASS, whenever 'inner' ring touches the boundary of outside area, even in one point, it is no more 'inner' ring, it is simply another area. A, B above can never be exported from GRASS as polygon A with inner ring B because there are only 2 areas A and B and no island.
+-----+-----+ | . | | . | +.....+.....+ | . | | x . | +-----+-----+ ---- road + boundary of one parcel => type boundary .... road => type line x parcel centroid (identifies whole area)Because lines are not used to build areas, we have only one area/centroid, instead of 4 which would be necessary in TIGER.
xx = Map.Att[Map.Area[area_num].att].x;
by new function
Vect_get_area_centroid()
Vect_get_centroid_coor()
/* types used in memory on run time - may change */
#define GV_POINT 0x01
#define GV_LINE 0x02
#define GV_BOUNDARY 0x04
#define GV_CENTROID 0x08
#define GV_FACE 0x10
#define GV_KERNEL 0x20
#define GV_AREA 0x40
#define GV_VOLUME 0x80
#define GV_POINTS (GV_POINT | GV_CENTROID )
#define GV_LINES (GV_LINE | GV_BOUNDARY )
struct line_cats
{
int *field; /* pointer to array of fields */
int *cat; /* pointer to array of categories */
int n_cats; /* number of vector categories attached to element */
int alloc_cats; /* allocated space */
};
int Vect_open_new (struct Map_info *, char name *, int with_z);
long Vect_write_line (struct Map_info *, int type, struct line_pnts *, struct line_cats *);
int Vect_read_next_line (struct Map_info *, struct line_pnts *, struct line_cats *);
struct line_cats *Vect_new_cats_struct (void);
int Vect_reset_cats (struct line_cats *);
int Vect_destroy_cats_struct (struct line_cats *);
int Vect_cat_set (struct line_cats *, int, int);
int Vect_cat_get (struct line_cats *, int, int *);
int Vect_cat_del (struct line_cats *, int);
int Vect_reset_cats (struct line_cats *);
And many, many others ...
For each pair map + field must be defined table, key column,
database, driver. This definition must be written to $MAPSET/DB text file.
Each row in DB file contains names separated by spaces in following order
([] - optional):
map[@mapset] field table [key [database [driver]]]
If key, database or driver are omited (on second and higher row only)
last definition is used. Definition from DB file in other mapset
may be overwritten by definition in current mapset if mapset is specified
with map name.
Wild cards * and ? may be used in map and mapset names.
Variables $GISDBASE, $LOCATION, $MAPSET, $MAP, $FIELD may be used in table, key, database and driver names. Note that $MAPSET is not current mapset but mapset of the map the rule is defined for.
Note that features in GRASS vector may have attributes in different tables or may be without attributes. Boundaries forms areas but it may happen that some boundaries are not closed (such boundaries would not appear in polygon layer). Boundaries may have attributes. All types may be mixed in one vector.
Link to the table is permanent and it is stored in 'dbln' file in vector directory. Tables are considered to be a part of the vector and g.remove, for example, deletes linked tables of the vector. Attributes must be joined with geometry.
* 1 tbl id $GISDBASE/$LOCATION/$MAPSET/vector/$MAP dbfThis definition says that entities with category of field 1 are linked to dbf tables with names tbl.dbf saved in vector directories of each map.
* 1 $MAP id $GISDBASE/$LOCATION/$MAPSET/dbf dbfSimilar as above but all dbf files are in one directory dbf/ in mapset and names of dbf files are $MAP.dbf
water* 1 rivers id /home/grass/dbf dbf water* 2 lakes lakeid /home/guser/mydb trans* 1 roads key basedb odbc trans* 5 railsThese definitions defines more fields for one map i.e. in one map may be more features linked to more tables. Definition on first 2 rows are applied for example on maps water1, water2, ... so that more maps may share one table.
water@PERMANENT 1 myrivers id /home/guser/mydbf dbfThis definion overwrites definition saved in PERMANENT/DB and links map from PERMANENT mapset to user's table.
Modules should be written so that connections to database for each vector field are independent. It should be possible to read attributes of input map from one database and write to some other and even with some other driver (should not be such problem).
There are open questions however. For example how to distinguish when
new table should be written and when not. For example definitions:
river 1 river id water odbc
river.backup* 1 NONE
could be used to say that tables should not be copied for backups of
map river because table is stored in reliable RDBMS.
Bounding box information was moved from coor file to topo file.
Ascii format in new version contains categories, new type centroid and z-coordinates. Points and centroids are saved as one coordinates pair instead of two. File is saved in old dig_ascii directory but the name will be probably changed.
ORGANIZATION DIGIT DATE DIGIT NAME MAP NAME MAP DATE MAP SCALE OTHER INFO ZONE WEST EDGE EAST EDGE SOUTH EDGE NORTH EDGE MAP THRESH
VERTI:followed by records of lines:
TYPE NUMBER_OF_COORDINATES [NUMBER_OF_CATEGORIES] Y X [Z] .... Y X [Z] [ FIELD CATEGORY] .... [ FIELD CATEGORY]Everything in [] is optional. TYPE may be:
P 1 1 1234 3435 1 354 L 3 1 4132 4534 1453 1454 1453 4543 1 355
Topology is always build by default if coor file was modified.
Dimension is kept. Input 2D vector is written as 2D, 3D as 3D.