1g.proj(1) GRASS GIS User's Manual g.proj(1)
2
6 g.proj - Prints or modifies GRASS projection information files (in
7 various co-ordinate system descriptions).
8 Can also be used to create new GRASS locations.
9
11 general, projection, create location
12
14 g.proj
15 g.proj --help
16 g.proj [-pgdjfwetc] [georef=file] [wkt=file] [proj4=params]
17 [epsg=code] [list_codes=string] [datum=name] [datum_trans=index]
18 [location=name] [--help] [--verbose] [--quiet] [--ui]
19 Flags:
21 -p
22 Print projection information in conventional GRASS format
23 -g
25 Print projection information in shell script style
26 -d
28 Verify datum information and print transformation parameters
29 -j
31 Print projection information in PROJ.4 format
32 -f
34 Print ’flat’ output with no linebreaks (applies to WKT and PROJ.4
35 output)
36 -w
38 Print projection information in WKT format
39 -e
41 Use ESRI-style format (applies to WKT output only)
42 -t
44 Force override of datum transformation information in input
45 co-ordinate system
46 -c
48 Modify current location projection files
49 --help
51 Print usage summary
52 --verbose
54 Verbose module output
55 --quiet
57 Quiet module output
58 --ui
60 Force launching GUI dialog
61 Parameters:
63 georef=file
64 Name of georeferenced data file to read projection information from
65 wkt=file
67 Name of ASCII file containing a WKT projection description
68 ’-’ for standard input
69 proj4=params
71 PROJ.4 projection description
72 ’-’ for standard input
73 epsg=code
75 EPSG projection code
76 Options: 1-1000000
77 list_codes=string
79 List codes for given authority, e.g. EPSG, and exit
80 Options: EPSG, ESRI, IGNF, OGC, PROJ
81 datum=name
83 Datum (overrides any datum specified in input co-ordinate system)
84 Accepts standard GRASS datum codes, or "list" to list and exit
85 datum_trans=index
87 Index number of datum transform parameters
88 "0" for unspecified or "-1" to list and exit
89 Options: -1-100
90 Default: 0
91 location=name
93 Name of new location to create
94
96 g.proj provides a means of converting a co-ordinate system description
97 (i.e. projection information) between various formats. If compiled
98 without OGR present, the functionality is limited to:
99 · Reporting the projection information for the current location,
101 either in conventional GRASS (-p flag) or PROJ (-j flag) format
102 · Changing the datum, or reporting and modifying the datum trans‐
104 formation parameters, for the current location
105 When compiled with OGR, functionality is increased and allows output of
107 the projection information in the Well-Known Text (WKT) format popu‐
108 larised by proprietary GIS. In addition, if one of the parameters geo‐
109 ref, wkt, proj4 or epsg is specified, rather than the projection infor‐
110 mation being read from the current location it is imported from an
111 external source as follows:
112 georef=filename
114 g.proj attempts to invoke GDAL and OGR in turn to read a georefer‐
115 enced file filename. The projection information will be read from
116 this file. If the file is not georeferenced or cannot be read, XY
117 (unprojected) will be used.
118 wkt=filename or -
120 The file filename should contain a projection description in WKT
121 format with or without line-breaks (e.g. a ’.prj’ file). If - is
122 given for the filename, the WKT description will be read from stdin
123 rather than a file.
124 proj4=description or -
126 description should be a projection description in PROJ format,
127 enclosed in quotation marks if there are any spaces. If - is given
128 for description, the PROJ description will be read from stdin
129 rather than as a directly-supplied command-line parameter.
130 epsg=number
132 number should correspond to the index number of a valid co-ordinate
133 system in the EPSG database. EPSG code support is based upon a
134 local copy of the GDAL CSV co-ordinate system and datum information
135 files, stored in the directory $GISBASE/etc/proj/ogr_csv. These can
136 be updated if necessary to support future revisions of the EPSG
137 database.
138 If datum information is incorrect or missing in the input co-ordinate
140 system definition (e.g. PROJ descriptions have very limited support for
141 specifying datum names), a GRASS datum abbreviation can instead be sup‐
142 plied using the datum parameter. This will override any datum contained
143 in the input co-ordinate system, and discard any datum transformation
144 parameters. Enter datum=list to return a list of all the datums sup‐
145 ported by GRASS. Since any existing datum transformation parameters
146 will have been discarded, the datumtrans parameter should in general
147 always be used in conjunction with datum.
148 The -p, -j, -w, etc. flags are all functional when importing projection
150 information from an external source, meaning that g.proj can be used to
151 convert between representations of the information. It is not required
152 that either the input or output be in GRASS format.
153 In addition however, if the -c flag is specified, g.proj will create
155 new GRASS projection files (PROJ_INFO, PROJ_UNITS, WIND and
156 DEFAULT_WIND) based on the imported information. If the location param‐
157 eter is specified in addition to -c, then a new location will be cre‐
158 ated. Otherwise the projection information files in the current loca‐
159 tion will be overwritten. The program will not warn before doing this.
160 The final mode of operation of g.proj is to report on the datum infor‐
162 mation and datum transformation parameters associated with the co-ordi‐
163 nate system. The -d flag will report a human-readable summary of this.
164
166 If the input co-ordinate system contains a datum name but no transfor‐
167 mation parameters, and there is more than one suitable parameter set
168 available (according to the files datum.table and datumtransform.table
169 in $GISBASE/etc/proj), g.proj will check the value of the datumtrans
170 option and act according to the following:
171 -1: List available parameter sets in a GUI-parsable (but also
172 human-readable) format and exit.
173 0 (default): Continue without specifying parameters - if used when cre‐
174 ating a location, other GRASS modules will use the "default" (likely
175 non-optimum) parameters for this datum if necessary in the future.
176 Any other number less than or equal to the number of parameter sets
177 available for this datum: Choose this parameter set and add it to the
178 co-ordinate system description.
179 If the -t flag is specified, the module will attempt to change the
180 datum transformation parameters using one of the above two methods even
181 if a valid parameter set is already specified in the input co-ordinate
182 system. This can be useful to change the datum information for an
183 existing location.
184 Output is simply based on the input projection information. g.proj does
186 not attempt to verify that the co-ordinate system thus described
187 matches an existing system in use in the world. In particular, this
188 means there are no EPSG Authority codes in the WKT output.
189 WKT format shows the false eastings and northings in the projected unit
191 (e.g. meters, feet) but in PROJ format it should always be given in
192 meters.
193 The maximum size of input WKT or PROJ projection descriptions is lim‐
195 ited to 8000 bytes.
196
198 Print information
199 Print the projection information for the current location:
200 g.proj -p
201 List the possible datum transformation parameters for the current loca‐
203 tion:
204 g.proj -t datumtrans=-1
205 Create projection (PRJ) file
207 Create a ’.prj’ file in ESRI format corresponding to the current loca‐
208 tion:
209 g.proj -wef > irish_grid.prj
210 Read projection from file
212 Read the projection information from a GeoTIFF file and print it in
213 PROJ format:
214 g.proj -jf georef=ASTER_DEM20020508161837.tif
215 Convert the PROJ projection description contained in a text file to WKT
217 format:
218 cat proj4.description | g.proj -w proj4=-
219 Create new location
221 Create a new location with the co-ordinate system referred to by EPSG
222 code 4326 (Latitude-Longitude/WGS84), without explicitly specifying
223 datum transformation parameters:
224 g.proj -c epsg=4326 location=latlong
225 Create a new location with the co-ordinate system referred to by
227 ESRI-EPSG code 900913 (Google Mercator Projection)
228 g.proj -c epsg=900913 location=google
229 Create a new location with the co-ordinate system referred to by EPSG
231 code 29900 (Irish Grid), selecting datum transformation parameter set
232 no. 2:
233 # list available datums for EPSG code 29900
234 g.proj -t datumtrans=-1 epsg=29900
235 g.proj -c epsg=29900 datumtrans=2 location=irish_grid
236 Create a new location with the same co-ordinate system as the current
238 location, but forcing a change to datum transformation parameter set
239 no. 1:
240 g.proj -c location=newloc -t datumtrans=1
241 Create a new location with the co-ordinate system from a WKT definition
243 stored in a text file:
244 g.proj -c wkt=irish_grid.prj location=irish_grid
245 Create a new location from a PROJ description, explicitly specifying a
247 datum and using the default datum transformation parameters:
248 g.proj -c location=spain proj4="+proj=utm +zone=30 +ellps=intl" datum=eur50 datumtrans=0
249 Using g.proj output for GDAL/OGR tools
251 Reproject external raster map to current GRASS projection (does not
252 always make sense!) using the GDAL ’gdalwarp’ tool. We recommend to
253 use the ERDAS/Img format and not to use the ESRI style of WKT:
254 # example for 30x30 pixel resolution (enforce with -tr to avoid odd values)
255 gdalwarp -of HFA -tr 30 30 -t_srs "`g.proj -wf`" aster.img aster_tmerc.img
256 Reproject external vector map to current GRASS projection using the OGR
258 ’ogr2ogr’ tool:
259 ogr2ogr -t_srs "`g.proj -wf`" polbnda_italy_GB_ovest.shp polbnda_italy_LL.shp
260
262 PROJ: Projection/datum support library
263 GDAL raster library and toolset
264 OGR vector library and toolset
265 Further reading
267 · ASPRS Grids and Datum
269 · MapRef - The Collection of Map Projections and Reference Sys‐
271 tems for Europe
272 · Projections Transform List (PROJ)
274
276 m.proj, r.proj, v.proj, r.import, r.in.gdal, v.import, v.in.ogr
277
279 Paul Kelly
280
282 Available at: g.proj source code (history)
283 Main index | General index | Topics index | Keywords index | Graphical
285 index | Full index
286 © 2003-2020 GRASS Development Team, GRASS GIS 7.8.5 Reference Manual
288GRASS 7.8.5 g.proj(1)