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This pages contains a growing list of Frequently Asked Questions (FAQs). Feel free to add text, "Edit" button for that. | This pages contains a growing list of Frequently Asked Questions (FAQs). Feel free to add text, "Edit" button for that. | ||
Hint: '''See also [[:Category: FAQ]] for more articles.''' | |||
=Usage= | =Usage= | ||
# In a site map, how to select all the points that are at the edge? - [[Points Edge Selection]] | |||
# How to create a buffer around polygons using v.buffer? - [[Vector Buffer]] | |||
# What are LOCATIONs and MAPSETs? - [[Location and Mapsets]] | |||
# Starting GRASS - [[Starting GRASS]] | |||
# ERROR: Default region not set - [[Error Region]] | |||
# Nothing shows in monitor window - [[Region Map]] | |||
# How to show labels, such as street labels on a vector map? - [[Labels Show]] | |||
# What is a raster MASK? - [[GRASS Raster Mask]] | |||
# What is an attribute? - [[GRASS Attributes]] | |||
# Is is possible to switch from one LOCATION to another while running GRASS? - [[Switch Locations]] | |||
# Changing region during operation? - [[Changing Region]] | |||
# Point in polygon test: - [[Point in Polygon]] | |||
# [[Georeferencing]] an image? | |||
# How do I reproject a raster or vector map? - [[Map Reprojection]] | |||
# How do I enjoy high quality statistic analysis in GRASS? [[GRASS and Rstat]] | |||
# What is the difference between pseudo-topological and real topological vect formats? - [[Topo Issue]] | |||
# How to to aggregate values from one polygon layer to another ? - [[Aggregate Values]] | |||
# How to diplay a vector (polygon) map colored by the attributes in a particular column? [[Vector Attribute Display]] | |||
# How to [[Convert vector types]] | |||
# How to [[Dissolve polygons]] | |||
# I get a "ERROR: G_realloc: unable to allocate 52980000 bytes of memory at lib/vector/diglib/cindex.c:113" or similar - [[Memory issues]] | |||
=Data= | =Data= | ||
# Can I map data from an arbitrary database model to work with GRASS without having to restructure or create a new database? | |||
# How can I drop columns in a sqlite-database? - [[Sqlite Drop Column]] | |||
# How to unlock SQLite database? - [[SQLite unlock database]] | |||
=Technical= | =Technical= | ||
# GRASS 6 symbols - [[IconSymbols]] | |||
# How do I compile/install GRASS GIS? [[Compile and Install]] | |||
Old stuff: | |||
# GRASS 5.7 vector architecture - [[Vector Faq GRASS57]] | |||
# Does GRASS 5.7 installation override my stable GRASS5x installation? [[GRASS5x and 57]] | |||
# Are GRASS 5.0.x/5.3.x/5.4.x raster maps compatible with GRASS57? Yes! | |||
=Installation= | =Installation= | ||
==GRASS 6 compilation problems== | ==GRASS 6 compilation problems== | ||
* ''Can't find a library even after I've built and installed it:'' Make sure that /usr/local/lib (or where you installed it) is listed in your /etc/ld.so.conf file and (as root) run /sbin/ldconfig. | * ''Can't find a library even after I've built and installed it:'' Make sure that /usr/local/lib (or where you installed it) is listed in your /etc/ld.so.conf file and (as root) run /sbin/ldconfig. | ||
<!-- | |||
# grass 5.7 compilation problems: - [[GRASS57 Compilation]] | |||
* How do I install grass in | # grass 5.3, 5.4 compilation problems: - [[GRASS53 Compilation]] | ||
--> | |||
* How do I install grass in MS Windows: - [[WinGRASS Installation]] | |||
==GRASS and Cygwin== | ==GRASS and Cygwin== | ||
# How do I find the [[Cygwin]] packages to install? - See [[Cygwin Packages]] | |||
# I can't find pq.dll: Make sure you installed the PostgreSQL package in the Cygwin [[http://geni.ath.cx/grass/setup-11.png installer]]. | |||
# I can't find pq.dll: try copy cygpq.dll to pq.dll | |||
= Errors = | |||
* In a Latitude-Longitude location I'm getting the error ''Illegal latitude for North'' when importing an unprojected raster image: Unprojected images are given a resolution of 1 pixel per line, and so any image with a height of more than 90 pixels will try and write data to an impossible latitude. | |||
<br> | |||
'''Solution''': import the image into a simple XY location and georeference the image with either r.region (if bounds are simple and known) or {{cmd|i.points}} and {{cmd|i.rectify}}. An automated alternative to {{cmd|r.region}} is to create a "World File" to be used by r.in.gdal. See the GeoTIFF format help page at http://www.gdal.org. | |||
: The command {{cmd|r.in.gdal}} has a ''-l'' flag to constrain the import to valid lat/lon ranges. Another good alternative is to use <tt>gdal_translate -a_ullr</tt> to convert the dataset into a GeoTiff with reset bounds. See the [[MODIS#Import|MODIS]] wiki page for details. | |||
: Use <tt>gdalinfo</tt> to test your data set. What it sees, ''r.in.gdal'' will see. | |||
: Sometimes you get this error if the input data tries to exist a little north-of-north and south-of-south. E.g. 90.5N - 90.5S. In these cases take care with the [[grid_registration|grid-versus-cell center]] raster convention when resetting the bounds. In GRASS the outer edge of all the cells are given as the n,s,e,w extent, and the data value for each cell represents the value within the area of all of that ewres*nsres cell. You might use <tt>gdal_translate -srcwin</tt> or <tt>-projwin</tt> to crop away the top/bottom row of cells so that the data does not try to place itself at an impossible latitude. | |||
[[Category:FAQ]] | |||
Latest revision as of 12:17, 2 October 2016
This pages contains a growing list of Frequently Asked Questions (FAQs). Feel free to add text, "Edit" button for that.
Hint: See also Category: FAQ for more articles.
Usage
- In a site map, how to select all the points that are at the edge? - Points Edge Selection
- How to create a buffer around polygons using v.buffer? - Vector Buffer
- What are LOCATIONs and MAPSETs? - Location and Mapsets
- Starting GRASS - Starting GRASS
- ERROR: Default region not set - Error Region
- Nothing shows in monitor window - Region Map
- How to show labels, such as street labels on a vector map? - Labels Show
- What is a raster MASK? - GRASS Raster Mask
- What is an attribute? - GRASS Attributes
- Is is possible to switch from one LOCATION to another while running GRASS? - Switch Locations
- Changing region during operation? - Changing Region
- Point in polygon test: - Point in Polygon
- Georeferencing an image?
- How do I reproject a raster or vector map? - Map Reprojection
- How do I enjoy high quality statistic analysis in GRASS? GRASS and Rstat
- What is the difference between pseudo-topological and real topological vect formats? - Topo Issue
- How to to aggregate values from one polygon layer to another ? - Aggregate Values
- How to diplay a vector (polygon) map colored by the attributes in a particular column? Vector Attribute Display
- How to Convert vector types
- How to Dissolve polygons
- I get a "ERROR: G_realloc: unable to allocate 52980000 bytes of memory at lib/vector/diglib/cindex.c:113" or similar - Memory issues
Data
- Can I map data from an arbitrary database model to work with GRASS without having to restructure or create a new database?
- How can I drop columns in a sqlite-database? - Sqlite Drop Column
- How to unlock SQLite database? - SQLite unlock database
Technical
- GRASS 6 symbols - IconSymbols
- How do I compile/install GRASS GIS? Compile and Install
Old stuff:
- GRASS 5.7 vector architecture - Vector Faq GRASS57
- Does GRASS 5.7 installation override my stable GRASS5x installation? GRASS5x and 57
- Are GRASS 5.0.x/5.3.x/5.4.x raster maps compatible with GRASS57? Yes!
Installation
GRASS 6 compilation problems
- Can't find a library even after I've built and installed it: Make sure that /usr/local/lib (or where you installed it) is listed in your /etc/ld.so.conf file and (as root) run /sbin/ldconfig.
- How do I install grass in MS Windows: - WinGRASS Installation
GRASS and Cygwin
- How do I find the Cygwin packages to install? - See Cygwin Packages
- I can't find pq.dll: Make sure you installed the PostgreSQL package in the Cygwin [installer].
- I can't find pq.dll: try copy cygpq.dll to pq.dll
Errors
- In a Latitude-Longitude location I'm getting the error Illegal latitude for North when importing an unprojected raster image: Unprojected images are given a resolution of 1 pixel per line, and so any image with a height of more than 90 pixels will try and write data to an impossible latitude.
Solution: import the image into a simple XY location and georeference the image with either r.region (if bounds are simple and known) or i.points and i.rectify. An automated alternative to r.region is to create a "World File" to be used by r.in.gdal. See the GeoTIFF format help page at http://www.gdal.org.
- The command r.in.gdal has a -l flag to constrain the import to valid lat/lon ranges. Another good alternative is to use gdal_translate -a_ullr to convert the dataset into a GeoTiff with reset bounds. See the MODIS wiki page for details.
- Use gdalinfo to test your data set. What it sees, r.in.gdal will see.
- Sometimes you get this error if the input data tries to exist a little north-of-north and south-of-south. E.g. 90.5N - 90.5S. In these cases take care with the grid-versus-cell center raster convention when resetting the bounds. In GRASS the outer edge of all the cells are given as the n,s,e,w extent, and the data value for each cell represents the value within the area of all of that ewres*nsres cell. You might use gdal_translate -srcwin or -projwin to crop away the top/bottom row of cells so that the data does not try to place itself at an impossible latitude.