OGR supports reading and writing primarily non-spatial tabular data stored in text CSV files. CSV files are a common interchange format between software packages supporting tabular data and are also easily produced manually with a text editor or with end-user written scripts or programs.
While in theory .csv files could have any extension, in order to auto-recognise the format OGR only supports CSV files ending with the extention ".csv". The datasource name may be either a single CSV file or point to a directory. For a directory to be recognised as a .csv datasource at least half the files in the directory need to have the extension .csv. One layer (table) is produced from each .csv file accessed.
Starting with GDAL 1.8.0, for files structured as CSV, but not ending with .CSV extension, the 'CSV:' prefix can be added before the filename to force loading by the CSV driver.
The OGR CSV driver supports reading and writing. Because the CSV format has variable length text lines, reading is done sequentially. Reading features in random order will generally be very slow. OGR CSV layer never have any coordinate system. When reading a field named "WKT" is assumed to contain WKT geometry, but also is treated as a regular field. The OGR CSV driver returns all attribute columns as string data types if no field type information file (with .csvt extension) is available.
Limited type recognition can be done for Integer, Real, String, Date (YYYY-MM-DD), Time (HH:MM:SS+nn) and DateTime (YYYY-MM-DD HH:MM:SS+nn) columns through a descriptive file with the same name as the CSV file, but a .csvt extension. In a single line the types for each column have to be listed with double quotes and be comma separated (e.g., "Integer","String"). It is also possible to specify explicitly the width and precision of each column, e.g. "Integer(5)","Real(10.7)","String(15)". The driver will then use these types as specified for the csv columns.
CSV files have one line for each feature (record) in the layer (table). The attribute field values are separated by commas. At least two fields per line must be present. Lines may be terminated by a DOS (CR/LF) or Unix (LF) style line terminators. Each record should have the same number of fields. Starting with GDAL 1.7.0, the driver will also accept a semicolon or a tabulation character as field separator . This autodetection will work only if there's no other potential separator on the first line of the CSV file. Otherwise it will default to comma as separator.
Complex attribute values (such as those containing commas, quotes or newlines) may be placed in double quotes. Any occurances of double quotes within the quoted string should be doubled up to "escape" them.
The driver attempts to treat the first line of the file as a list of field names for all the fields. However, if one or more of the names is all numeric it is assumed that the first line is actually data values and dummy field names are generated internally (field_1 through field_n) and the first record is treated as a feature. Starting with GDAL 1.9.0 numeric values are treated as field names if they are enclosed in double quotes.
All CSV files are treated as UTF-8 encoded. Starting with GDAL 1.9.0, a Byte Order Mark (BOM) at the beginning of the file will be parsed correctly. From 1.9.2, The option WRITE_BOM can be used to create a file with a Byte Order Mark, which can improve compatibility with some software (particularly Excel).Example (employee.csv):
ID,Salary,Name,Comments 132,55000.0,John Walker,"The ""big"" cheese." 133,11000.0,Jane Lake,Cleaning Staff
Note that the Comments value for the first data record is placed in double quotes because the value contains quotes, and those quotes have to be doubled up so we know we haven't reached the end of the quoted string yet.
Many variations of textual input are sometimes called Comma Separated Value files, including files without commas, but fixed column widths, those using tabs as separators or those with other auxiliary data defining field types or structure. This driver does not attempt to support all such files, but instead to support simple .csv files that can be auto-recognised. Scripts or other mechanisms can generally be used to convert other variations into a form that is compatible with the OGR CSV driver.
It is possible to extract spatial information (points) from a CSV file which has columns for the X and Y coordinates, through the use of the VRT driver.
Consider the following CSV file (test.csv):
Latitude,Longitude,Name 48.1,0.25,"First point" 49.2,1.1,"Second point" 47.5,0.75,"Third point"You can write the associated VRT file (test.vrt):
<OGRVRTDataSource> <OGRVRTLayer name="test"> <SrcDataSource>test.csv</SrcDataSource> <GeometryType>wkbPoint</GeometryType> <LayerSRS>WGS84</LayerSRS> <GeometryField encoding="PointFromColumns" x="Longitude" y="Latitude"/> </OGRVRTLayer> </OGRVRTDataSource>and ogrinfo -ro -al test.vrt will return :
OGRFeature(test):1 Latitude (String) = 48.1 Longitude (String) = 0.25 Name (String) = First point POINT (0.25 48.1 0) OGRFeature(test):2 Latitude (String) = 49.2 Longitude (String) = 1.1 Name (String) = Second point POINT (1.1 49.200000000000003 0) OGRFeature(test):3 Latitude (String) = 47.5 Longitude (String) = 0.75 Name (String) = Third point POINT (0.75 47.5 0)
The driver supports creating new databases (as a directory of .csv files), adding new .csv files to an existing directory or .csv files or appending features to an existing .csv table. Deleting or replacing existing features is not supported.
Layer Creation options:
The driver supports reading and writing to files managed by VSI Virtual File System API, which include "regular" files, as well as files in the /vsizip/ (read-write) , /vsigzip/ (read-only) , /vsicurl/ (read-only) domains.
Writing to /dev/stdout or /vsistdout/ is also supported.
ogr2ogr -f CSV output.csv input.shp -lco GEOMETRY=AS_XYZ