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Merge pull request #532 from ccrook/delimited_text_bug_fixes
Three delimited text bug fixes, GUI tidyup, context help fix
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resources/context_help/QgsDelimitedTextSourceSelect-en_US
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<h3>Delimited Text File Layer</h3> | ||
Loads and displays delimited text files | ||
<p> | ||
<a href="#re">Overview</a><br/> | ||
<a href="#creating">Creating a delimited text layer</a><br/> | ||
<a href="#csv">How the delimiter, quote, and escape characters work</a><br /> | ||
<a href="#regexp">How regular expression delimiters work</a><br /> | ||
<a href="#wkt">How WKT text is interpreted</a><br /> | ||
<a href="#example">Example of a text file with X,Y point coordinates</a><br/> | ||
<a href="#wkt_example">Example of a text file with WKT geometries</a><br/> | ||
<a href="#notes">Notes</a><br/> | ||
</p> | ||
|
||
<h4><a name="re">Overview</a></h4> | ||
<p>A "delimited text file" contains data in which each record starts on a new line, and | ||
is split into fields by a delimiter such as a comma. | ||
This type of file is commonly exported from spreadsheets (for example CSV files) or databases. | ||
Typically the first line of a delimited text file contains the names of the fields. | ||
</p> | ||
<p> | ||
Delimited text files can be loaded into QGIS as a layer. | ||
The records can be displayed spatially either as a point | ||
defined by X and Y coordinates, or using a Well Known Text (WKT) definition of a geometry which may | ||
describe points, lines, and polygons of arbitrary complexity. The file can also be loaded as an attribute | ||
only table, which can then be joined to other tables in QGis. | ||
</p> | ||
<p> | ||
In addition to the geometry definition the file can contain text, integer, and real number fields. QGis | ||
will choose the type of field based on its contents. | ||
</p> | ||
<h4><a name="creating">Creating a delimited text layer</a></h4> | ||
<p>Creating a delimited text layer involves choosing the data file, defining the format (how each record is to | ||
be split into fields), and defining the geometry is represented. | ||
This is managed with the delimited text dialog as detailed below. | ||
The dialog box displays a sample from the beginning of the file which shows how the format | ||
options have been applied. | ||
</p> | ||
<h5>Choosing the data file</h5> | ||
<p>Use the "Browse..." button to select the data file. Once the file is selected the | ||
layer name will automatically be populated based on the file name. The layer name is used to represent | ||
the data in the QGis legend. | ||
</p> | ||
<p> | ||
By default files are assumed to be encoded as UTF-8. However other file | ||
encodings can be selected. For example "System" uses the default encoding for the operating system. | ||
If you are expecting to move the QGis project then it is safer to use a specific encoding. | ||
</p> | ||
<h5>Specifying the file format</h5> | ||
<p>The file format can be one of | ||
<ul> | ||
<li>CSV file format. This is a format commonly used by spreadsheets, in which fields are delimited | ||
by a comma character, and quoted using a "(quote) character. Within quoted fields, a quote | ||
mark is entered as "".</li> | ||
<li>Selected delimiters. Each record is split into fields using one or more delimiter character. | ||
Quote characters are used for fields which may contain delimiters. Escape characters may be used | ||
to treat the following character as a normal character (ie to include delimiter, quote, and | ||
new line characters in text fields). The use of delimiter, quote, and escape characters is detailed <a href="#csv">below</a>. | ||
<li>Regular expression. Each line is split into fields using a "regular expression" delimiter. | ||
The use of regular expressions is details <a href="#regexp">below</a>. | ||
</ul> | ||
<h5>Record and field options</h5> | ||
<p>The following options affect the selection of records and fields from the data file</p> | ||
<ul> | ||
<li>Number of header lines to discard: used to skip over header lines at the beginning of the text file</li> | ||
<li>First record has fields names: if selected then the first record in the file (after the skipped lines) is interpreted as names of fields, rather than as a data record.</li> | ||
<li>Trim fields: if selected then leading and trailing whitespace characters will be removed from each field (except quoted fields). </li> | ||
<li>Discard empty fields: if selected then empty fields (after trimming) will be discard. This | ||
affects the alignment of data into fields and is equivalent to treating consecutive delimiters as a | ||
single delimiter. Quoted fields are never discarded.</li> | ||
<li>Decimal point is comma: if selected then commas in real numbers represent the decimal point. For | ||
example "-51,354" is equivalent to -51.354. | ||
</li> | ||
</ul> | ||
<h5>Geometry definition</h5> | ||
<p>The geometry is can be define as one of</p> | ||
<ul> | ||
<li>Point coordinates: each feature is represented as a point defined by X and Y coordinates.</li> | ||
<li>Well known text (WKT) geometry: each feature is represented as a well known text string, for example | ||
"POINT(1.525622 51.20836)". See details of the <a href="#wkt">well known text</a> format. | ||
<li>No geometry (attribute only table): records will not be displayed on the map, but can be viewed | ||
in the attribute table and joined to other layers in QGis</li> | ||
</ul> | ||
<p>For point coordinates the following options apply:</p> | ||
<ul> | ||
<li>X field: specifies the field containing the X coordinate</li> | ||
<li>Y field: specifies the field containing the Y coordinate</li> | ||
<li>DMS angles: if selected coordinates are represented as degrees/minutes/seconds | ||
or degrees/minutes. QGis is quite permissive in its interpretation of degrees/minutes/seconds. | ||
A valid DMS coordinate will contain three numeric fields with an optional hemisphere prefix or suffix | ||
(N, E, or + are positive, S, W, or - are negative). Additional non numeric characters are | ||
generally discarded. For example "N41d54'01.54"" is a valid coordinate. | ||
</li> | ||
</ul> | ||
<p>For well known text geometry the following options apply:</p> | ||
<ul> | ||
<li>Geometry field: the field containing the well known text definition.</li> | ||
<li>Geometry type: one of "Detect" (detect), "Point", "Line", or "Polygon". | ||
QGis layers can only display one type of geometry feature (point, line, or polygon). This option selects | ||
which geometry type is displayed in text files containing multiple geometry types. Records containing | ||
other geometry types are discarded. | ||
If "Detect" is selected then the type of the first geometry in the file will be used. | ||
"Point" includes POINT and MULTIPOINT WKT types, "Line" includes LINESTRING and | ||
MULTLINESTRING WKT types, and "Polygon" includes POLYGON and MULTIPOLYGON WKT types. | ||
</ul> | ||
|
||
<h4><a name="csv">How the delimiter, quote, and escape characters work</a></h4> | ||
<p>Records are split into fields using three character sets: delimiter characters, quote characters, | ||
and escape characters. Quote and escape characters cannot be the same as delimiter characters - they | ||
will be ignored if they are. Escape characters can be the same as quote characters, but behave differently | ||
if they are.</p> | ||
<p>The delimiter characters are used to mark the end of each field. If more than one delimiter character | ||
is defined then any one of the characters can mark the end of a field. The quote and escape characters | ||
can override the delimiter character, so that it is treated as a normal character.</p> | ||
<p>Quote characters may be used to mark the beginning and end of quoted fields. Quoted fields can | ||
contain delimiters and may span multiple lines in the text file. If a field is quoted then it must | ||
start and end with the same quote character. Quote characters cannot occur within a field unless they | ||
are escaped.</p> | ||
<p>Escape characters which are not quote characters force the following character to be treated normally | ||
(that is, to stop it being treated as a new line, delimiter, or quote character). | ||
</p> | ||
<p>If a quote character is also an escape character, then it can be represented in a quoted field by | ||
entering it twice. For example if ' is a quote character and an escape character, then the string | ||
'Smith''s Creek' will represent the value Smith's Creek. | ||
</p> | ||
<h4><a name="regexp">How regular expression delimiters work</a></h4> | ||
<p>Regular expressions are mini-language used to represent character patterns. There are many variations | ||
of regular expression syntax - QGis uses the syntax provided by the <a href="http://qt-project.org/doc/qt-4.8/qregexp.html">QRegExp</a> class of the <a href="http://qt.digia.com">Qt</a> framework.</p> | ||
<p>In a regular expression delimited file each line is treated as a record. Each match of the regular expression in the line is treated as the end of a field.</p> | ||
|
||
<h4><a name="wkt">How WKT text is interpreted</a></h4> | ||
<p> | ||
The delimited text layer recognizes the following | ||
<a href="http://en.wikipedia.org/wiki/Well-known_text">well known text</a> types - | ||
POINT, MULTIPOINT, LINESTRING, MULTILINESTRING, POLYGON, and MULTIPOLYGON. It will accept geometries with | ||
a Z coordinate (eg "POINT Z"), a measure ("POINT M"), or both ("POINT ZM"). | ||
</p> | ||
<p> | ||
It can also handle the PostGIS EWKT variation, in which the geomtry is preceded by an spatial reference | ||
system id (eg "SRID=4326;POINT(175.3 41.2)"), and a variant used by Informix in which the WKT is | ||
preceded by an integer spatial reference id (eg "1 POINT(175.3 41.2)"). | ||
In both cases the SRID is ignored. | ||
</p> | ||
<h4><a name="example">Example of a text file with X,Y point coordinates</a></h4> | ||
<pre> | ||
X;Y;ELEV<br /> | ||
-300120;7689960;13<br /> | ||
-654360;7562040;52<br /> | ||
1640;7512840;3<br /> | ||
</pre> | ||
<p>This file:</p> | ||
<ul> | ||
<li> Uses <b>;</b> as delimiter. Any character can be used to delimit the fields.</li> | ||
<li>The first row is the header row. It contains the field names X, Y and ELEV.</li> | ||
<li>No quotes (") are used to delimit text fields.</li> | ||
<li>The x coordinates are contained in the X field.</li> | ||
<li>The y coordinates are contained in the Y field.</li> | ||
</ul> | ||
<h4><a name="wkt_example">Example of a text file with WKT geometries</a></h4> | ||
<pre> | ||
id|wkt<br /> | ||
1|POINT(172.0702250 -43.6031036)<br /> | ||
2|POINT(172.0702250 -43.6031036)<br /> | ||
3|POINT(172.1543206 -43.5731302)<br /> | ||
4|POINT(171.9282585 -43.5493308)<br /> | ||
5|POINT(171.8827359 -43.5875983)<br /> | ||
</pre> | ||
<p>This file:</p> | ||
<ul> | ||
<li>Has two fields defined in the header row: id and wkt. | ||
<li>Uses <b>|</b> as a delimiter.</li> | ||
<li>Specifies each point using the WKT notation | ||
</ul> |
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