[mapserver-commits] r8314 - trunk/docs
svn at osgeo.org
svn at osgeo.org
Mon Dec 29 12:42:59 EST 2008
Author: hobu
Date: 2008-12-29 12:42:59 -0500 (Mon, 29 Dec 2008)
New Revision: 8314
Added:
trunk/docs/faq.txt
Modified:
trunk/docs/documentation.txt
trunk/docs/index.txt
Log:
add the FAQ
Modified: trunk/docs/documentation.txt
===================================================================
--- trunk/docs/documentation.txt 2008-12-29 14:43:16 UTC (rev 8313)
+++ trunk/docs/documentation.txt 2008-12-29 17:42:59 UTC (rev 8314)
@@ -11,6 +11,7 @@
about
introduction
installation/index
+ faq
mapfile/index
mapscript/index
input/index
Added: trunk/docs/faq.txt
===================================================================
--- trunk/docs/faq.txt (rev 0)
+++ trunk/docs/faq.txt 2008-12-29 17:42:59 UTC (rev 8314)
@@ -0,0 +1,672 @@
+.. _faq:
+
+***************************************************
+ FAQ
+***************************************************
+
+Where is the MapServer log file?
+-------------------------------------------------------------------------------
+
+See :ref:`rfc28`
+
+What books are available about MapServer?
+-------------------------------------------------------------------------------
+
+`"Mapping Hacks" <http://www.oreilly.com/catalog/mappinghks/>`__ by Schuyler
+Erle, Rich Gibson, and Jo Walsh is available from O'Reilly.
+
+`"Web Mapping Illustrated" <http://oreilly.com/catalog/webmapping>`__ by Tyler
+Mitchell is available from O'Reilly. Introduces MapServer and many other
+related technologies including, GDAL/OGR, MapScript, PostGIS, map projections,
+etc.
+
+`"MapServer: Open Source GIS Development"
+<http://www.apress.com/book/bookDisplay.html?bID=443>`__ by Bill Kropla.
+
+
+How do I compile MapServer for Windows?
+-------------------------------------------------------------------------------
+
+See :ref:`win32`. Also, you can use the development libraries in :ref:`osgeo4w`
+as a starting point instead of building all of the dependent libraries yourself.
+
+What do MapServer version numbers mean?
+-------------------------------------------------------------------------------
+
+MapServer's version numbering scheme is very similar to Linux's. For example,
+a MapServer version number of 4.2.5 can be decoded as such:
+
+- 4: Major version number. MapServer releases a major version every two to
+ three years.
+- 2: Minor version number. Increments in minor version number almost always
+ relate to additions in functionality.
+- 5: Revision number. Revisions are bug fixes only. No new functionality is
+ provided in revisions.
+
+From a developer's standpoint, MapServer version numbering scheme is also like
+Linux. Even minor version numbers (0..2..4..6) relate to *release* versions,
+and odd minor versions (1..3..5..7) correspond to developmental versions.
+
+Is MapServer Thread-safe?
+-------------------------------------------------------------------------------
+
+**Q**: Is MapServer thread-safe?
+
+**A**: Generally, no (but see the next question). Many components of MapServer
+use static or global data that could potentially be modified by another
+thread. Under heavy load these unlikely events become inevitable, and could
+result in sporadic errors.
+
+**Q**: Is it possible to safely use any of MapServer in a multi-threaded
+application?
+
+**A**: Some of it, yes, with care. Or with Python :) Programmers must either
+avoid using the unsafe components of MapServer or carefully place locks around
+them. Python's global interpreter lock immunizes against MapServer threading
+problems; since no mapscript code ever releases the GIL all mapscript
+functions or methods are effectively atomic. Users of mapscript and Java,
+.NET, mod_perl, or mod_php do not have this extra layer of protection.
+
+**A**: Which components are to be avoided?
+
+**Q**: Below are lists of unsafe and unprotected components and unsafe but
+locked components.
+
+Unsafe:
+
+- OGR layers: use unsafe CPL services
+- Cartoline rendering: static data
+- Imagemap output: static data
+- SWF output: static data and use of unsafe msGetBasename()
+- SVG output: static data
+- WMS/WFS server: static data used for state of dispatcher
+- Forcing a temporary file base (an obscure feature): static data
+- MyGIS: some static data
+
+Unsafe, but locked:
+
+- Map config file loading: global parser
+- Setting class and and layer filter expressions (global parser)
+- Class expression evaluation (global parser)
+- Setting map and layer projections (PROJ)
+- Raster layer rendering and querying (GDAL)
+- Database Connections (mappool.c)
+- PostGIS support
+- Oracle Spatial (use a single environment handle for connection)
+- SDE support (global layer cache)
+- Error handling (static repository of the error objects)
+- WMS/WFS client connections: potential race condition in Curl initialization
+- Plugin layers (static repository of the loaded dll-s)
+
+Rather coarse locks are in place for the above. Only a single thread can use
+the global parser at a time, and only one thread can access GDAL raster data
+at a time. Performance is exchanged for safety.
+
+What does STATUS mean in a LAYER?
+-------------------------------------------------------------------------------
+
+STATUS ON and STATUS OFF set the default status of the layer. If a map is
+requested, those layers will be ON/OFF unless otherwise specified via the
+layers parameter. This is particularly the case when using Mapscript and
+Mapserver's built-in template mechanism, but is also useful as a hint when
+writing your own apps and setting up the initial map view.
+
+STATUS DEFAULT means that the layer is always on, even if not specified in the
+layers parameter. A layer's status can be changed from DEFAULT to OFF in
+Mapscript, but other than that, it's always on.
+
+:ref:`cgi` turns everything off that is not "STATUS DEFAULT" off so all layers
+start from the same state (e.g. off) and must be explicitly requested to be
+drawn or query. That common state made (at least in my mind) implementations
+easier. I mean, if a layer "lakes" started ON the doing layer=lakes would turn
+it OFF. So I wanted to remove the ambiguity of a starting state.
+
+How can I make my maps run faster?
+-------------------------------------------------------------------------------
+
+There are a lot of different approaches to improving the performance of your
+maps, aside from the obvious and expensive step of buying faster hardware.
+Here are links to some individual howtos for various optimizations.
+
+* :ref:`Tuning your mapfile for performance <mapfile_tuning>`
+* :ref:`Optimizing the performance of vector data sources <vector_optimization>`
+* :ref:`Optimizing the performance of raster data sources <raster_optimization>`
+* :ref:`Tileindexes for mosaicing and performance <tileindex>`
+
+Some general tips for all cases:
+
+* First and foremost is hardware. An extra GB of RAM will give your map
+ performance increases beyond anything you're likely to achieve by tweaking
+ your data. With the price of RAM these days, it's cheap and easy to speed up
+ every map with one inexpensive upgrade.
+
+* Use the scientific method. Change one thing at a time, and see what effect
+ it had. Try disabling all layers and enabling them one at a time until you
+ discover which layer is being problematic.
+
+* Use :ref:`shp2img` program to time your results. This runs from
+ the command line and draws an image of your entire map. Since it's run from
+ the command line, it is immune to net lag and will give more consistent
+ measurements that your web browser.
+
+What does Polyline mean in MapServer?
+-------------------------------------------------------------------------------
+
+There's confusion over what POLYLINE means in MapServer and via ESRI. In
+MapServer POLYLINE simply means a linear representation of POLYGON data. With
+ESRI polyline means multi-line. Old versions of the Shapefile techical
+description don't even refer to polyline shapefiles, just line. So, ESRI
+polyline shapefiles are just linework and can only be drawn and labeled as
+LINE layers. Those shapefiles don't have feature closure enforced as polygon
+shapefiles do which is why the distinction is so important. I suppose there is
+a better choice than POLYLINE but I don't know what it would be.
+
+.. note::
+ The only difference between POLYLINE and LINE layers is how they are
+ labeled.
+
+What is MapScript?
+-------------------------------------------------------------------------------
+
+MapScript is the scripting interface to MapServer, usually generated by
+:term:`SWIG` (except in the case of :ref:`php`). MapScript allows you to
+program with MapServer's objects directly instead of interacting with
+MapServer through its :ref:`cgi` and :ref:`mapfile`.
+
+
+Does MapServer support reverse geocoding?
+-------------------------------------------------------------------------------
+
+No.
+
+Reverse geocoding is an activity where you take a list of street features that
+you already have and generate postal addresses from them. This kind of spatial
+functionality is provided by proprietary packages such as the ESRI suite of
+tools, as well as services such as those provided by GDT. MapServer is for
+*map rendering*, and it does not provide for advanced spatial operations such
+as this.
+
+Does MapServer support geocoding?
+-------------------------------------------------------------------------------
+
+No.
+
+Geocoding is an activity where you take a list of addresses and generate
+lat/lon points for them. This kind of spatial functionality is provided by
+proprietary packages such as the ESRI suite of tools, as well as services such
+as those provided by GDT. MapServer is for *map rendering*, and it does not
+provide for advanced spatial operations such as this.
+
+If you are using MapScript, there is a free geocder available through XMLRPC
+and SOAP at http://geocoder.us . You could hook you application up to use this
+service to provide lat/lon pairs for addresses, and then use MapServer to
+display those points.
+
+How do I set line width in my maps?
+-------------------------------------------------------------------------------
+
+You must set the symbol for the LAYER to be 'circle' and then you can set the
+symbol SIZE to be the width you want. A 'circle' symbol can be defined as
+
+.. code-block:: mapfile
+
+ SYMBOL
+ NAME 'circle'
+ TYPE ELLIPSE
+ FILLED TRUE
+ POINTS 1 1 END
+ END
+
+Why do my JPEG input images look crappy via MapServer?
+-------------------------------------------------------------------------------
+
+The default output format for MapServer is 8bit pseudo-colored PNG or GIF.
+Inherently there will be some color degredation in converting a 24bit image
+(16 million colors) image into 8bit (256 colors).
+
+But in order to ensure fast rendering MapServer uses quite a simple method to
+do the transformation, converting pixels to the nearest color in a 175 color
+colorcube. This will usually result in blotchy color in a fairly smoothly
+varying image.
+
+Solutions include:
+
+- Select 24bit output. This might be as easy as "IMAGETYPE JPEG" in your MAP
+ section.
+- Enable dithering (PROCESSING "DITHER=YES") to produce a better color
+ appearance.
+- Preprocess your image to 8bit before using it in MapServer with an external
+ application like the GDAL rgb2pct.py script.
+
+For more information review the :ref:`raster`.
+
+Which image format should I use?
+-------------------------------------------------------------------------------
+
+Although Mapscript can generate the map in any desired image format it
+sufficient to only consider the three most prevalent ones: JPEG, PNG, and GIF.
+
+JPEG is an image format that uses a lossy compression algorithm to reduce an
+image's file size and is mostly used when loss of detail through compression
+is either not noticeable or negligible, as in most photos. Maps on the other
+hand mainly consist of fine lines and areas solidly filled in one colour,
+which is something JPEG is not known for displaying very well. In addition,
+maps, unless they include some aerial or satellite imagery, generally only use
+very few different colours. JPEG with its 24bit colour depth capable of
+displaying around 16.7 million colours is simple not suitable for this
+purpose. GIF and PNG however use an indexed colour palette which can be
+optimized for any number (up to 256) of colours which makes them the perfect
+solution for icons, logos, charts or maps. The following comparison (generated
+file sizes only; not file generation duration) will therefore only include
+these two file formats:
+
+.. table:: GIF vs. PNG vs. PNG24 Generated Map File Sizes
+
+ +------------------------------------------+-------+-------+-------+
+ | | GIF | PNG | PNG24 |
+ +==========================================+=======+=======+=======+
+ |Vector Data only | 59kb | 26kb | 69kb |
+ +------------------------------------------+-------+-------+-------+
+ |Vector Data & Satellite Image coloured | 156kb | 182kb | 573kb |
+ +------------------------------------------+-------+-------+-------+
+ |Vector Data & Satellite Image monochrome | 142kb | 134kb | 492kb |
+ +------------------------------------------+-------+-------+-------+
+
+(results based on an average 630x396 map with various colours, symbols,
+labels/annotations etc.)
+
+Although GIF shows a quantitative as well as qualitative advantage over PNG
+when generating maps that contain full coloured remote sensing imagery, PNG is
+the clear quantitative winner in terms of generated file sizes for maps with
+or without additional monochrome imagery and should therefore been the
+preferred image format. If the mapping application however can also display
+fullcolour aerial or satellite imagery, the output file format can be changed
+dynamically to either GIF or even PNG24 to achieve the highest possible image
+quality.
+
+Why doesn't PIL (Python Imaging Library) open my PNGs?
+-------------------------------------------------------------------------------
+
+`PIL <http://www.pythonware.com/products/pil/>`__ does not support interlaced
+PNGs at this time (no timetable on when it actually will either). To be able
+to read PNGs in PIL, they must not be interlaced. Modify your OUTPUTFORMAT with
+a FORMATOPTION like so:
+
+.. code-block:: mapfile
+
+ OUTPUTFORMAT
+ NAME png
+ DRIVER "GD/PNG"
+ MIMETYPE "image/png"
+ IMAGEMODE RGB
+ EXTENSION "png"
+ FORMATOPTION "INTERLACE=OFF"
+ END
+
+Why do my symbols look poor in JPEG output?
+-------------------------------------------------------------------------------
+
+When I render my symbols to an 8bit output (PNG, GIF) they look fine, but in
+24bit jpeg output they look very blocky and gross.
+
+In order to render some classes of symbols properly in 24bit output, such as
+symbols from true type fonts, it is necessary to force rendering to occur in
+RGBA. This can be accomplished by including the "TRANSPARENCY ALPHA" line in
+the layer definition. Don't use this unnecessarily as there is a performance
+penalty.
+
+This problem also affects PNG24 output or any RGB output format. 8bit (PC256)
+or RGBA output types are already ok.
+
+How do I add a copyright notice on the corner of my map?
+-------------------------------------------------------------------------------
+
+You can use an inline feature, with the :ref:`FEATURE` object, to make a point on
+your map. Use the TEXT parameter of the FEATURE object for the actual text of
+the notice, and a :ref:`LABEL` object to style the notice.
+
+Example Layer
+...............................................................................
+
+.. code-block:: mapfile
+
+ LAYER
+ NAME "copyright"
+ STATUS ON
+ TYPE annotation
+ TRANSFORM ll #set the image origin to be lower left
+ FEATURE
+ POINTS
+ 60 -10 #set the offset from lower left position in pixels
+ END
+ TEXT "© xyz company 2006" #this is your displaying text
+ END
+ CLASS
+ LABEL #defines the font, colors etc. of the text
+ FONT "sans"
+ TYPE TRUETYPE
+ SIZE 8
+ BUFFER 1
+ COLOR 0 0 0
+ BACKGROUNDCOLOR 255 255 255
+ FORCE TRUE
+ END
+ END
+ UNITS PIXELS #sets the units for the feature object
+ END
+
+Result
+...............................................................................
+
+.. image:: ./images/copyright-image.png
+
+
+How do I have a polygon that has both a fill and an outline with a width?
+-------------------------------------------------------------------------------
+
+How do I have a polygon that has both a fill and an outline with a width?
+Whenever I put both a color (fill) and an outlinecolor with a width on a
+polygon within a single STYLE, the outline width isn't respected.
+
+For historical reasons, width has two meanings within the context of filling
+polygons and stroke widths for the outline. If a polygon is filled, then the
+width defines the width of the symbol *inside* the filled polygon. In this
+event, the outline width is disregarded, and it is always set to 1. To acheive
+the effect of *both* a fill and an outline width, you need to use two styles
+in your class.
+
+.. code-block:: mapfile
+
+ STYLE # solid fill
+ COLOR 255 0 0
+ END
+ STYLE # thick outline (could use a circle symbol with size too)
+ OUTLINECOLOR 0 0 0
+ WIDTH 3
+ ANTIALIAS TRUE
+ END
+
+How can I create simple antialiased line features?
+-------------------------------------------------------------------------------
+
+The easiest way to produce antialiased lines is to:
+
+- use a 24-bit output image type (IMAGEMODE RGB (or RGBA))
+- set TRANSPARENCY ALPHA in the layer using antialiased lines
+- set ANTIALIAS TRUE in the STYLE element of the CLASS with antialiased lines
+
+The following mapfile snippets enable antialiased county borders:
+
+.. code-block:: mapfile
+
+ ...
+ IMAGETYPE "png24"
+ ...
+ OUTPUTFORMAT
+ NAME "png24"
+ DRIVER "GD/PNG"
+ MIMETYPE "image/png"
+ IMAGEMODE RGB
+ EXTENSION "png"
+ END
+ ...
+ LAYER
+ NAME "counties"
+ TYPE line
+ STATUS default
+ DATA "bdry_counln2"
+ TRANSPARENCY alpha
+ SYMBOLSCALE 5000000
+ CLASS
+ STYLE
+ WIDTH 3
+ COLOR 1 1 1
+ ANTIALIAS true
+ END
+ END
+ END
+ ...
+
+.. note::
+ The bdry_counln2 shapefile referenced in the counties layer is a line
+ shapefile. A polygon shapefile could be substituted with roughly the same
+ results, though owing to the nature of shapefiles each border would be
+ rendered twice and the resulting output line would likely appear to be
+ slightly thicker. Alternatively, one could use a polygon shapefile, set
+ TYPE to POLYGON, and use OUTLINECOLOR in place of COLOR in the STYLE
+ element.
+
+.. note::
+ You can tweak the combination of STYLE->WIDTH and SYMBOLSCALE to modify
+ line widths in your output images.
+
+.. seealso::
+ :ref:`Cartoline <sym_construction>` symbols can be used to achieve fancier
+ effects.
+
+Which OGC Specifications does MapServer support?
+-------------------------------------------------------------------------------
+
+* Web Map Service (OGC:WMS) 1.0.0, 1.0.7, 1.1.0 and 1.1.1
+* Web Feature Service (OGC:WFS) 1.0.0, 1.1.0
+* Web Coverage Service (OGC:WCS) 1.0.0, 1.1.0
+* Geography Markup Language (OGC:GML) 2.1.2, 3.1.0 Level 0 Profile
+* Web Map Context Documents (OGC:WMC) 1.0.0, 1.1.0
+* Styled Layer Descriptor (OGC:SLD) 1.0.0
+* Filter Encoding Specification (OGC:FES) 1.0.0
+* Sensor Observation Service (OGC:SOS) 0.1.2b, 1.0.0
+* OWS Common (OGC:OWS) 1.0.0, 1.1.0
+
+Why does my requested WMS layer not align correctly?
+-------------------------------------------------------------------------------
+
+Requesting a layer from some ArcIMS WMS connectors results in a map with
+misalgned data (the aspect ratio of the pixels looks wrong).
+
+Some ArcIMS sites are not set up to stretch the returned image to fit the
+requested envelope by default. This results in a map with data layers that
+overlay well in the center of the map, but not towards the edges. This can be
+solved by adding "*reaspect=false*" to the request (by tacking it on to the
+connection string).
+
+For example, if your mapfile is in a projection other than EPSG:4326, the
+following layer will not render correctly:
+
+.. code-block:: mapfile
+
+ LAYER
+ NAME "hillshade"
+ TYPE RASTER
+ STATUS OFF
+ TRANSPARENCY 70
+ CONNECTIONTYPE WMS
+ CONNECTION "http://gisdata.usgs.net:80/servlet19/com.esri.wms.Esrimap/USGS_WMS_NED?"
+ PROJECTION
+ "init=epsg:4326"
+ END
+ METADATA
+ "wms_srs" "EPSG:4326"
+ "wms_title" "US_NED_Shaded_Relief"
+ "wms_name" "US_NED_Shaded_Relief"
+ "wms_server_version" "1.1.1"
+ "wms_format" "image/png"
+ END
+ END
+
+Adding "reaspect=false" to the connection string solves the problem:
+
+.. code-block:: mapfile
+
+ LAYER
+ NAME "hillshade"
+ TYPE RASTER
+ STATUS OFF
+ TRANSPARENCY 70
+ CONNECTIONTYPE WMS
+ CONNECTION "http://gisdata.usgs.net:80/servlet19/com.esri.wms.Esrimap/USGS_WMS_NED?reaspect=false"
+ PROJECTION
+ "init=epsg:4326"
+ END
+ METADATA
+ "wms_srs" "EPSG:4326"
+ "wms_title" "US_NED_Shaded_Relief"
+ "wms_name" "US_NED_Shaded_Relief"
+ "wms_server_version" "1.1.1"
+ "wms_format" "image/png"
+ END
+ END
+
+When I do a GetCapabilities, why does my browser want to download mapserv.exe/mapserv?
+---------------------------------------------------------------------------------------
+
+A beginner question here... I'm new to MS and to Apache. I've got MS4W up and
+running with the Itasca demo. Now I want to enable it as a WMS server. mapserv
+-v at the command line tells me it supports WMS_SERVER. When I point my
+browser to it, my browser just wants to download mapserv.exe!
+
+What am I missing?
+
+Here is the URL I'm using to issue a GetCapabilities WMS request:
+http://localhost/cgi-bin/mapserv.exe?map=../htdocs/itasca/demo.map&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetCapabilities
+
+The OGC:WMS 1.1.0 and 1.1.1 specifications (which are both supported by
+MapServer) state that, for GetCapabilities responses, the OGC:WMS server
+returns a specific MIME type (i.e. application/vnd.ogc.xml (see subclause
+6.5.3 of `OGC:WMS 1.1.1
+<http://portal.opengeospatial.org/files/?artifact_id=1081&version=1&format=pdf>`__.
+
+A MIME type is passed from the web server to the client (in your case, a web
+browser), from which a client can decide how to process it.
+
+Example 1: if using a web browser, if a web server returns an HTTP Header of
+"Content-type:image/png", then the web browser will know that this is a PNG
+image and display it accordingly.
+
+Example 2: if using a web browser, if a web server returns an HTTP Header of
+"Content-type:text/html", then the web browser will know that this is an HTML
+page and display it accordingly (i.e. tables, divs, etc.)
+
+Basically, what is happening is that the OGC:WMS is returning, in the headers
+of the HTTP response, a MIME type which your web browser does not understand,
+which usually prompts a dialog box on whether to open or download the content
+(i.e. Content-type:application/vnd.ogc.wms_xml).
+
+You could configure your web browser to handle the application/vnd.ogc.wms_xml
+MIME type a certain way (i.e. open in Notepad, etc.).
+
+Why do my WMS GetMap requests return exception using MapServer 5.0?
+-------------------------------------------------------------------------------
+
+Before upgrading to MapServer 5.0, I was able to do quick GetMap tests in the
+form of:
+http://wms.example.com/wms?service=WMS&version=1.1.1&request=GetMap&layers=foo
+
+Now when I try the same test, MapServer WMS returns an XML document saying
+something about missing required parameters. What's going on here?
+
+This was a major change for WMS Server support in MapServer 5.0. MapServer WMS
+Server GetMap requests now require the following additional parameters:
+
+* srs
+* bbox
+* width
+* height
+* format
+* styles
+
+.. note::
+ These parameters were always required in all versions of the WMS
+ specification, but MapServer previously had not required them in a client
+ request (even though most OGC WMS clients would issue them anyway to be
+ consistent with the WMS spec).
+
+The request below now constitutes a valid GetMap request:
+
+::
+
+ http://wms.example.com/wms?service=WMS&version=1.1.1&request=GetMap&layers=foo&srs=EPSG:4326&bbox=-180,-90,180,90&format=image/png&width=400&height=300&styles=default
+
+Which is consistent with the WMS specification.
+
+More information on these parameters can be found in the :ref:`wms_server` and
+the `OGC WMS 1.1.1 specification
+<http://portal.opengeospatial.org/files/?artifact_id=1081&version=1&format=pdf>`__
+
+For more detailed information, see `ticket 1088
+<http://trac.osgeo.org/mapserver/ticket/1088>`__
+
+.. warning::
+ STYLES, though a required WMS parameter, is now optional again in
+ MapServer. For more detailed information, see `ticket 2427
+ <http://trac.osgeo.org/mapserver/ticket/2427#comment:2>`__
+
+Where do I find my :term:`EPSG` code?
+-------------------------------------------------------------------------------
+
+There is a text file "epsg" in your PROJ4 installation (e.g.
+"/usr/local/share/proj/epsg") which contain the EPSG information used by
+PROJ4. In Windows, this is often located in C:\\proj\\nad or is found with an
+environment variable called PROJ_LIB.
+
+http://spatialreference.org allows you to search for EPSG codes.
+
+You can also have a look at:
+http://ocean.csl.co.uk
+
+More information to EPSG:
+http://www.epsg.org
+
+More information to PROJ4:
+http://trac.osgeo.org/proj
+
+How can I reproject my data using ogr2ogr?
+-------------------------------------------------------------------------------
+
+With ogr2ogr of course! ogr2ogr is a powerful utility that will transform the
+projections of your shapefiles when passed the appropriate parameters. In my
+case, I was using Mapserver to serve data in RI State Plane Feet. In order to
+do so, the data had to first be converted to meters. Here is the command I
+used:
+
+::
+
+ ogr2ogr -t_srs EPSG:32130 output.shp input.shp
+
+Since my data already had a projection defined, I did not need to explicitly
+state a source projection. This command uses the EPSG definition for NAD83
+Rhode Island (32130) and performs the feet to meters conversion.
+
+Now say my data wasn't already projected? Here's how we deal with that:
+
+::
+
+ ogr2ogr -s_srs "+proj=tmerc +lat_0=41.08333333333334 +lon_0=-71.5 +k=0.999994 +x_0=100000 +y_0=0 +ellps=GRS80 +datum=NAD83 +to_meter=0.3408 +no_defs" -t_srs EPSG:32130 output.shp input.shp
+
+Let's examine what is going on here:
+
+The -s_srs parameter explicitly defines a projection for the data. The
+parameters used here were taken out of the EPSG definition (in this case,
+32130) in the epsg file(see the `projection FAQ <epsg_codes>`__ for more
+details on locating EPSG definitions). The entry for RI in the epsg file is as
+follows:
+
+::
+
+ # NAD83 / Rhode Island
+ <32130> +proj=tmerc +lat_0=41.08333333333334 +lon_0=-71.5 +k=0.999994 +x_0=100000 +y_0=0 +ellps=GRS80 +datum=NAD83 +units=m +no_defs no_defs <>
+
+You can see how the definition in the initial command is formulated. Notice
+that the "+units=m" parameter has been changed to “+to_meter=0.3408”. This is
+important for the conversion. Where did the value of 0.3408 come from you ask?
+From the EPSG file! It has many goodies buried in it so by simply running
+'grep "to_meter" epsg’ you can refresh your memory if you need to.
+
+The next parameter in the command is "-t_srs EPSG:32130". This command tells
+ogr2ogr to transform the data to the EPSG code of 32130. After this is
+declared, all you need to do is declare a file name for your new shape file
+and to set which file is being used as the input (note: make sure you don’t
+confuse the order of these two).
+
+Hit enter, bombs away, and enjoy your new data in meters!
+
+
Modified: trunk/docs/index.txt
===================================================================
--- trunk/docs/index.txt 2008-12-29 14:43:16 UTC (rev 8313)
+++ trunk/docs/index.txt 2008-12-29 17:42:59 UTC (rev 8314)
@@ -32,10 +32,16 @@
Download source and binaries by navigating to :ref:`download`.
+About
+-------------------------------------------------------------------------------
+
+Find out more about MapServer :ref:`here <about>`
+
.. warning::
This website is a preview of the upcoming version of the MapServer
website. It is not expected to go "live" until Dec 30th, 2008.
+
.. _GIS: http://en.wikipedia.org/wiki/Geographic_information_system
.. _`Open Source`: http://www.opensource.org
.. _`Recreation Compass`: http://www.dnr.state.mn.us/maps/compass.html
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