Difference between revisions of "Gis Concepts/id"

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(New page: {{Trans|Bahasa Indonesia}} == Geodesy and Cartography == === Background material === * [http://oceanservice.noaa.gov/education/kits/geodesy/welcome.html An introduction to Geodesy] from ...)
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{{Trans|Bahasa Indonesia}}
{{Trans|Bahasa Indonesia}}

== Geodesy and Cartography ==
== Geodesi dan Kartografi ==
=== Background material ===
=== Bahan pengantar ===

* [http://oceanservice.noaa.gov/education/kits/geodesy/welcome.html An introduction to Geodesy] from NOAA
* [http://oceanservice.noaa.gov/education/kits/geodesy/welcome.html Pendahuluan tentang Geodesi] dari NOAA
* [http://en.wikipedia.org/wiki/Geodesy Wikipedia's Geodesy entry]
* [http://en.wikipedia.org/wiki/Geodesy Literatur tentang Geodesi dari Wikipedia]
* [http://en.wikipedia.org/wiki/GIS Wikipedia's GIS entry]
* [http://en.wikipedia.org/wiki/GIS Literatur tentang GIS dari Wikipedia]
* [http://earth-info.nima.mil/GandG/publications/ NGA Geodesy and Geophysics publications]  
* [http://earth-info.nima.mil/GandG/publications/ Publikasi tentang Geodesi dan Geofisik dari NGA]  
* [http://www.ordnancesurvey.co.uk/oswebsite/gps/information/coordinatesystemsinfo/guidecontents/index.html UK Ordnance Survey primer on coordinate system concepts] ([http://www.ordnancesurvey.co.uk/gps/docs/A_Guide_to_Coordinate_Systems_in_Great_Britain.pdf PDF])
* [http://www.ordnancesurvey.co.uk/oswebsite/gps/information/coordinatesystemsinfo/guidecontents/index.html UK Ordnance Survey primer tentang konsep sistem koordinat] ([http://www.ordnancesurvey.co.uk/gps/docs/A_Guide_to_Coordinate_Systems_in_Great_Britain.pdf PDF])

=== Map projections ===
=== Proyeksi peta ===

* [http://www.asprs.org/resources/grids/ ASPRS Grids and Datums]: detailed descriptions of national projections
* [http://www.asprs.org/resources/grids/ ASPRS Grid dan Datum]: deskripsi detil tentang proyeksi nasional
* [http://www.mapref.org/ MapRef] - The Collection of Map Projections and Reference Systems for Europe
* [http://www.mapref.org/ MapRef] - Koleksi Proyeksi Peta dan Sistem Referensi untuk Eropa
* [http://www.remotesensing.org/geotiff/proj_list/ Projections Transform Lists] (PROJ4)  
* [http://www.remotesensing.org/geotiff/proj_list/ Daftar Transformasi Proyeksi] (PROJ4)  
* [http://www.dmap.co.uk/utmworld.htm UTM Zones]
* [http://www.dmap.co.uk/utmworld.htm Zone UTM]

* [http://www.epsg.org EPSG projection codes]
* [http://www.epsg.org Kode proyeksi EPSG]
: [http://www.epsg-registry.org/ EPSG database search]
: [http://www.epsg-registry.org/ Pencarian basisdata EPSG]
: [http://spatialreference.org/ Spatialreference community portal]
: [http://spatialreference.org/ Portal komunitas Spatialreference]

Projection galleries:
Galeri Proyeksi:
* [http://www.progonos.com/furuti/MapProj/CartIndex/cartIndex.html Map projection concepts] by Carlos Furuti
* [http://www.progonos.com/furuti/MapProj/CartIndex/cartIndex.html Konsep proyeksi peta] oleh Carlos Furuti
* [http://www.csiss.org/map-projections/index.html Map projection gallery] by Paul Anderson ([http://www.galleryofmapprojections.com/ old link])
* [http://www.csiss.org/map-projections/index.html Galeri proyeksi peta] oleh Paul Anderson ([http://www.galleryofmapprojections.com/ old link])
<!-- retained the old link as new one seems to lead to a dead server -->
<!-- retained the old link as new one seems to lead to a dead server -->

=== Map datums ===
=== Datum peta ===

* [http://www.colorado.edu/geography/gcraft/notes/datum/datum.html An introduction to geodetic datums] by Peter Dana
* [http://www.colorado.edu/geography/gcraft/notes/datum/datum.html Pengantar tentang datum geodetik] oleh Peter Dana
* [http://home.online.no/~sigurdhu/WGS84_Eng.html How WGS 84 defines the Earth]
* [http://home.online.no/~sigurdhu/WGS84_Eng.html Bagaimana WGS 84 mendefinisikan Bumi]
* A discussion of [http://www.linz.govt.nz/core/surveysystem/geodeticinfo/conversions/datums/nzgd1949-nzgd2000/index.html 3-term, 7-term, and NTv2 grid datum transformations] by Land Information New Zealand
* A discussion of [http://www.linz.govt.nz/core/surveysystem/geodeticinfo/conversions/datums/nzgd1949-nzgd2000/index.html 3-term, 7-term, dan NTv2 transformasi datum grid] oleh Land Information New Zealand
: (besides the web page have a look at the PDF fact sheet and guide linked therein)
: (besides the web page have a look at the PDF fact sheet and guide linked therein)
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Revision as of 15:43, 30 September 2008

This page is in progress of translating to Bahasa Indonesia.

Geodesi dan Kartografi

Bahan pengantar

Proyeksi peta


Pencarian basisdata EPSG
Portal komunitas Spatialreference

Galeri Proyeksi:

Datum peta

(besides the web page have a look at the PDF fact sheet and guide linked therein)

How GRASS deals with geodetics

As far as GRASS is concerned, an ellipsoid and a spheroid are the same thing, and ellipsoid is the prefered name.

As far as GRASS is concerned, a datum is made up of an ellipsoid and an origin. Setting a datum is optional, but highly recommended.

GRASS uses a modified version of the PROJ.4 library.

Modules controling a location's map projection

Modules for reprojecting GIS maps and data

  • r.proj for reprojecting raster maps
  • v.proj for reprojecting vector maps
  • m.proj for reprojecting a list of coordinate pairs

Modules for georectifying images

  • r.region for resetting a raster map's bounds information
  • gis.m GIS manager GeoReferencing tool (File menu)
  • i.points and i.vpoints for setting GCPs
  • i.rectify for georectifying imagery
  • GDALwarp (use with gdal_translate, see the i.warp script in the wiki AddOns page)

GIS Data types

Raster Data

Data which occurs in a regularly spaced grid. e.g. a satellite image or digital terrain map.
Region settings determine the spatial extent and resolution of the grid.

Raster Intro

Replacement raster format

GRASS Raster Mask

GRASS raster semantics

3D Raster Data (Voxel)

A stack of 2D raster maps.

Raster 3D Intro

Vector Data

Data which occurs as a series of coordinates. e.g. a GPS position or coastline map. May be a point, line, area, etc in either 2D or 3D space. Generally independent of region settings.

Vector Intro


Imagery Data

Pixelated photographic or satellite images, often imported from a GeoTIFF or PNG image file.

As far as the GIS is concerned this is just another raster map, but there are several modules specially tailored for rectification and processing common imagery types. e.g. ortho-photos or multi-channel LANDSAT data.

Site Data

Old versions of GRASS (5 and earlier) treated point data separate to line and polygon data. GRASS 6 classes all vector data features the same. Convert old sites file data into GRASS 6 vector format with the GRASS 6 v.in.sites or v.in.sites.all modules.

Conversions between data types

The following table is intended to catalog transformations from one type of data to another:
[table is currently incomplete!]

From / To Raster 3D Raster Vector
Raster r.mapcalc r.to.rast3 r.to.vect, v.sample, r.volume
3D Raster r3.to.rast, r3.cross.rast r3.mapcalc
Vector v.to.rast, v.surf.rst, v.surf.idw v.vol.rst, v.vol.idw, v.to.rast3 v.clean
Data r.in.* r3.in.* v.in.*

How a GRASS project is organized

GRASS data is stored in a three level structure, the database, location and mapset. These can be found in a series of nested directories on the user's computer. All three must exist and are set at GRASS startup time.

The Database

The directory in which all GIS data is to be stored.

e.g. ~/grassdata/

The Location

A location is a GRASS project consisting of an area, projection definition (or unprojected), a grouping of mapsets, all with the same projection settings. A location is a subdirectory of the GRASS database.

e.g. world_lat_lon, utm_zone_59, or west_coast

A location contains one or many mapsets.

The Mapset

A mapset contains map(s), it is a subdirectory of a location. Conceptually, if several mapsets are used in a location, they may be assigned to different users (each has one or several own mapsets to work in and cannot modify thos of other users), and/or it they are used to organize a project (location) by subareas or subprojects. There are no specific organizational limitations.

There is always a PERMANENT mapset which is readable from all other mapsets within the same location. Read access to maps in other mapsets is managed with the 'g.mapsets' command or by adding the "@" symbol and mapset name (e.g. map@othermapset).

How the Open Source software development model works

GRASS differs from many other GIS software packages used in the professional world in that it is developed and distributed by users for users; mostly on a volunteer basis, in the open, and is given away for free.

Emphasis is placed on interoperability and unlimited access to data as well as software flexibility and evolution rate (both added features and bug minimization).

Free can have many meanings, as the links below illustrate, and within a project there is often a spectrum of philosophies and goals amongst developers. But it works - Free Software has revolutionized many sectors of the computing world over the last few years and continues to do so today.

Raster GIS Analysis

Simple Raster Math

Sometimes when analyzing the relationship between two or more raster data sets, a relatively simple mathematical approach is best. One example using the r.mapcalc tool would be to look at changes between two raster data sets. By subtracting the values in these two data sets you can assume that resulting cells with a positive value have a possitive change and those with a negative value have negative change. If the cell values have a zero value then there would be no change.

GRASS comes bundled with the r.mapcalc tool as well as the d.m GUI interface for the tool accessable using the r.mapcalculator command. This GUI allows the user to easily assign raster sets to the variables used in the formulas and easily create mathematical strings that will result in a new raster data set containing the results.