GRASS and Python/ko

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파이선 분과회

파이선 분과회 단체들(Python Special Interest Groups)은 파이선의 개발, 개선, 세부적인 관리를 위해 상호 노력합니다. 각각의 분과회는 분과회의, 조정자, 메일 리스트, 파이선 웹사이트의 디렉토리를 가집니다. 분과회 회원권은 비형식적이며 SIG 메일링 리스트에 등록하는 경우 자동으로 획득됩니다. 어떤 분이라도 분과회에 가입할 수 있으며, 분화회의 메일링 목록을 이용하여 개발자 회의에 참가할 수 있습니다. 아래 연걸사이트에서 현재 활동중인 분과회 회원들의 주소과 그들이 소유한 리소스에 접근할 수 있습니다.

더 상세한 사항은 다음 사이트에서 참조 http://www.python.org/community/sigs/

GRASS 환경하에서 파이선 스크립트 작성

파이선은 셀스크립트보다 강력하며 또한 C에 비하여 매우 쉽습니다. 파이선 스크립트는 g.parser로 처리할 수 있는 간단한 모듈 정의를 포함합니다. 아래에 그 예제가 있습니다. 이러한 방법을 이용하면 별도 프로그램이 없어도 GUI를 구현할 수 있습니다. 또한 입력을 체크하고 스케레톤???외형???, 도움말 쪽을 자동으로 작성할 수 있습니다. 이에 더하여 이것은??? 그라스 메시지 번역시스템에 연결됩니다. 스크립트 ("scripting")용 라이버리를 "grass.script", 로 다음과 같이 사용할 수 있습니다. 전형적인 사용예로: 

import grass.script as grass

관련 파일이 $GISBASE/etc/python/grass/script/*.py 에 있습니다. 더 상세한 이해를 도모하려면 다음을 이용하십시오.

노트: C 강점을 이용하여야만 하는 코드을 작성하려면, 여러분은 다음 사이트를 통하여 GRASS C 라이버러리 함수를 사용할 수 있습니다. For code which needs access to the power of C, you can access the GRASS C library functions via the Python "ctypes" interface.

Python script editor파이선 구문 편집기

GRASS 6.4.3+의 레이어관리 wxGUI 는 파이선 셀을 가지고 있어 wxGUI환경하에서 사용자가 직접 파이선 구문을 작성할 수 있게 합니다.

Embedded interactive Python Shell in wxGUI Layer Manager
Embedded interactive Python Shell in wxGUI Layer Manager

Using the GRASS Python Scripting Library GRASS 파이선 구문 라이버러리

당신은 그라스 세션중에서 쉽게 파이선 구문을 수행할 수 있습니다. You can run Python scripts easily in a GRASS session.

구문들을 작성하려면, To write these scripts,

  • 파이선 내부에서 사용된 그라스 구문을 지원하기 위해서 grass.script를 제공하는 lib/python/의 라이버러리를 조사하십시오. which provides grass.script in order to support GRASS scripts written in Python.
 참조 GRASS Python Scripting Library를 통하여 노트와 예제를 익히십시오.  for notes and examples.
  • 그라스의 디렉토리 scripts/에 최종 사용자에게 제공되는 다수의 예제 시리즈가 있습니다. directory of GRASS contains a series of examples actually provided to the end users.

바람직한 파이선 코드 체계를 보려면, 다음 사이트를 보십시오.For the desired Python code style, have a look at SUBMITTING_PYTHON.

외부에서 그라스 함수를 호출하는 파이선 구문의 작성 Creating Python scripts that call GRASS functionality from outside

Note: This is a more advanced use case of using GRASS' functionality from outside via Python. Commonly, a user will run GRASS Python script from inside a GRASS session, i.e. either from the command line or from the Python shell embedded in the wxGUI (screenshot).

For calling GRASS functionality from outside, see also Working with GRASS without starting it explicitly.

MS-원도우

외부에서 파이선을 이용하여 그라스 함수를 사용하려면 몇몇의 환경변수를 설정하여야 합니다. In order to use GRASS functionality via Python from outside, some environment variables have to be set: 

GISBASE= C:\GRASS-64
GISRC= C:\Documents and Settings\user\.grassrc6
LD_LIBRARY_PATH= C:\GRASS-64\lib
PATH= C:\GRASS-64\etc;C:\GRASS-64\etc\python;C:\GRASS-64\lib;C:\GRASS-64\bin;C:\GRASS-64\extralib;C:\GRASS-64\msys\bin;C:\Python26;
PYTHONLIB= C:\Python26
PYTHONPATH= C:\GRASS-64\etc\python
GRASS_SH= C:\GRASS-64\msys\bin\sh.exe

Some hints약간의 힌트:

  1. The ".grassrc6" file listed above must exist. Run GRASS one time interactively to create it or see below for how to writing it
  2. The Python interpreter (python.exe) needs to be in the PATH
  3. Python needs to be associated with the .py extension
  4. PATHEXT needs to include .py if you want to be able to omit the extension
  5. PYTHONPATH needs to be set to %GISBASE%\etc\python

Points 2-4 should be taken care of by the Python installer. 5 needs to be done by the startup (currently, this doesn't appear to be the case on MS-Windows).

Alternatively to run GRASS interactively, you can also create the ".grassrc6" file yourself, e.g. (update to existing directory for "grassdata"): 

GISDBASE: C:\Documents and Settings\user\grassdata
LOCATION_NAME: nc_spm_08
MAPSET: user1
GRASS_DB_ENCODING: ascii

It doesn't matter what the file is called, so long as %GISRC% points to it and it contains the necessary settings.

The normal location for GRASS 6.x on Windows is: 

%APPDATA%\GRASS6\grassrc6

On Windows 7, a typical setting for %APPDATA% is 

C:\Users\<username>\AppData\Roaming

Linux

In order to use GRASS functionality via Python from outside, some environment variables have to be set: 

export GISBASE="/usr/local/grass-6.4.svn/"
export PATH="$PATH:$GISBASE/bin:$GISBASE/scripts"
export LD_LIBRARY_PATH="$LD_LIBRARY_PATH:$GISBASE/lib"
# for parallel session management, we use process ID (PID) as lock file number:
export GIS_LOCK=$$
# path to GRASS settings file
export GISRC="$HOME/.grassrc6"
export PYTHONPATH="$PYTHONPATH:$GISBASE/etc/python"

Running external commands from Python

For information on running external commands from Python, see: http://docs.python.org/lib/module-subprocess.html

Avoid using the older os.* functions. Section 17.1.3 lists equivalents using the Popen() interface, which is more robust (particularly on Windows).

Testing and installing Python extensions

Debugging

Make sure the script is executable: 

   chmod +x /path/to/my.extension.py

During development, a Python script can be debugged using the Python Debugger (pdb): 

   python -m pdb /path/to/my.extension.py input=my_input_layer output=my_output_layer option=value -f

Installation

Once you're happy with your script, you can put it in the scripts/ folder of your GRASS install. To do so, first create a directory named after your extension, then create a Makefile for it, and a HTML man page: 

   cd /path/to/grass_src/
   cd scripts
   ls # It is useful to check out the existing scripts and their structure
   mkdir my.extension
   cd my.extension
   cp path/to/my.extension.py .
   touch my.extension.html
   touch Makefile

Next step is to edit the Makefile. It is a very simple text file, the only thing to check is to put the right extension name (WITHOUT the .py file extension) after PGM: 

   MODULE_TOPDIR = ../..
   
   PGM = my.extension
   
   include $(MODULE_TOPDIR)/include/Make/Script.make
   
   default: script

The HTML file would be generated automatically. If you want to add more precisions in it, you can do it (just make sure you start at DESCRIPTION. See existing scripts.)

You can then run "make" within the my.extension folder. Running "make" in the extension directory places the resulting files in the staging directory (path/to/grass_src/dist.<YOUR_ARCH>/). If you're running GRASS from the staging directory (/path/to/grass_src/bin.<YOUR_ARCH>/grass7), subsequent commands will used the updated files. 

   # in your extension directory (/path/to/grass_src/scripts/my.extension/)
   make
   # Starting GRASS from the staging directory
   /path/to/grass_src/bin.<YOUR_ARCH>/grass7
   my.extension help

You can also run "make install" from the top level directory of your GRASS install (say /usr/local/src/grass_trunk/). Running "make install" from the top level just copies the whole of the dist.<YOUR_ARCH>/ directory to the installation directory (e.g. /usr/local/grass70) and the bin.<YOUR_ARCH>/grass70 bin file to the bin directory (e.g. /usr/local/bin), and fixes any embedded paths in scripts and configuration files. 

   cd /path/to/grass_src
   make install
   # Starting GRASS as usual would work and show your extension available
   grass7
   my.extension help

Python extensions in GRASS GIS

Python Scripting Library

pygrass Library

Python Ctypes Interface

This interface allows calling GRASS library functions from Python scripts. See Python Ctypes Examples for details.

Examples:

  • Latest and greatest: GRASS 7 Python scripts

Sample script for GRASS 6 raster access (use within GRASS, Spearfish session): 

#!/usr/bin/env python

## TODO: update example to Ctypes

import os, sys
from grass.lib import grass

if "GISBASE" not in os.environ:
    print "You must be in GRASS GIS to run this program."
    sys.exit(1)

if len(sys.argv)==2:
  input = sys.argv[1]
else:
  input = raw_input("Raster Map Name? ")

# initialize
grass.G_gisinit('')

# find map in search path
mapset = grass.G_find_cell2(input, '')

# determine the inputmap type (CELL/FCELL/DCELL) */
data_type = grass.G_raster_map_type(input, mapset)

infd = grass.G_open_cell_old(input, mapset)
inrast = grass.G_allocate_raster_buf(data_type)

rown = 0
while True:
    myrow = grass.G_get_raster_row(infd, inrast, rown, data_type)
    print rown, myrow[0:10]
    rown += 1
    if rown == 476:
        break

grass.G_close_cell(inrast)
grass.G_free(cell)

Sample script for vector access (use within GRASS, Spearfish session): 

#!/usr/bin/python

# run within GRASS Spearfish session
# run this before starting python to append module search path:
#   export PYTHONPATH=/usr/src/grass70/swig/python
#   check with "import sys; sys.path"
# or:
#   sys.path.append("/usr/src/grass70/swig/python")
# FIXME: install the grass bindings in $GISBASE/lib/ ?

import os, sys
from grass.lib import grass
from grass.lib import vector as grassvect

if "GISBASE" not in os.environ:
    print "You must be in GRASS GIS to run this program."
    sys.exit(1)

if len(sys.argv)==2:
  input = sys.argv[1]
else:
  input = raw_input("Vector Map Name? ")

# initialize
grass.G_gisinit('')

# find map in search path
mapset = grass.G_find_vector2(input,'')

# define map structure
map = grassvect.Map_info()

# define open level (level 2: topology)
grassvect.Vect_set_open_level (2)

# open existing map
grassvect.Vect_open_old(map, input, mapset)

# query
print 'Vect map: ', input
print 'Vect is 3D: ', grassvect.Vect_is_3d (map)
print 'Vect DB links: ', grassvect.Vect_get_num_dblinks(map)
print 'Map Scale:  1:', grassvect.Vect_get_scale(map)
print 'Number of areas:', grassvect.Vect_get_num_areas(map)

# close map
grassvect.Vect_close(map)

wxPython GUI development

Python-GRASS add-ons

Stand-alone addons:

Using GRASS gui.tcl in Python

Here is some example code to use the grass automatically generated guis in python code. This could (should) all be bundled up and abstracted away so that the implementation can be replaced later. 

import Tkinter
import os

# Startup (once):

tk = Tkinter.Tk()
tk.eval ("wm withdraw .")
tk.eval ("source $env(GISBASE)/etc/gui.tcl")
# Here you could do various things to change what the gui does
# See gui.tcl and README.GUI

# Make a gui (per dialog)
# This sets up a window for the command.
# This can be different to integrate with tkinter:
tk.eval ('set path ".dialog$dlg"')
tk.eval ('toplevel .dialog$dlg')
# Load the code for this command:
fd = os.popen ("d.vect --tcltk")
gui = fd.read()
# Run it
tk.eval(gui)
dlg = tk.eval('set dlg') # This is used later to get and set 

# Get the current command in the gui we just made:
currentcommand = tk.eval ("dialog_get_command " + dlg)

# Set the command in the dialog we just made:
tk.eval ("dialog_set_command " + dlg + " {d.vect map=roads}")

FAQ

  • Q: Error message오류 사항??? "execl() failed: Permission denied" - 무엇으로 해결하나?
A: Be sure that the execute bit of the script is set. 당신 스크립트의 실행비트가 결정되었는지 확인하세요???

연결

일반 안내

프로그래밍

  • Python and Statistics:
    • RPy - Python interface to the R-statistics programming language

발표문헌

From FOSS4G2006:

참고문헌

  • Zambelli, P., Gebbert, S., Ciolli, M., 2013. Pygrass: An Object Oriented Python Application Programming Interface (API) for Geographic Resources Analysis Support System (GRASS) Geographic Information System (GIS). ISPRS International Journal of Geo-Information 2, 201–219. (DOI | PDF)
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