your east and north coordinates and import your value as a floating point attribute, so your data in GRASS sites format will look like this:

namemygrasssites

descIs.in.ascii sites=mygrasssites input=myasciisites fs=space 3246000 I 5877000 I #1 %23 3246012.515877012.5#2 %24.4 3246025 I 5877025#3 %22.3

If the input point data include a third dimension (depth, elevation) and the values are separated by commas (CSV format), you can import them with s.in.ascii, using the parameter d for setting the number of dimensions and fs for a delimiter as follows:

s.in.ascii sites=grasssites3d input=myasciisites3d d=3 fs=,

Depending on application, elevation z can be handled either as a third dimension or as a floating point attribute

As we have shown in the Section 5.1.6, UNIX provides an effective tool for working with ASCII data called awk. You can use it to modify your ASCII data to conform to the GRASS site format. For example, if your data in points.dat are organized as:

ID north east elevation

you can remove the ID and change the order of coordinates as required by

GRASS using:

cat points.dat awk Iprint $3, $2, $4} s.in.ascii mysites

which writes the values from the third (east), second (north) and fourth (elevation) column and then imports this file by s.in.ascii. You will find more detailed explanation of awk and related examples in Appendix A which describes the use of UNIX text editing tools.

Importing site data in geographical coordinates. Latitude-longitude data can be imported either in DD format (decimal degree, see Section 2.2.2) with longitude given in the first and latitude in the second column:

8.314824 54.921730 sitel 8.897605 54.872353 site2 9.549371 54.834080 site3

or in DMS (degree, minutes, seconds) format:

18:53.3664E 54:55:18.228N sitel 53:51.378E 54 : 52:20.471N site2 32:57.7356E 54:50:02.688N site3

The module s.in.ascii will accept point data written in any of these two formats.

NOTES

1 GDAL library, http: www.remotesensing.org/gdal/

2 Spearfish 10 m LatLong/NAD83 DEM ArcGRID coverage file, section data sets, http: mpa.itc.it/grasstutor/

3 Netpbm tools, http: sourceforge.net/projects/netpbm/

4 The RMS error represents the distance of the set matching point towards the ideal placed matching point. It is calculated through:

rms= {x-XorigY + [y-yohgf-

5 GSHHS shoreline data Web site, http: www.soest.hawaii.edu/wessel/gshhs/gshhs.html

4.3.3 Export of sites data

Site data can be exported to an external ASCII file by s.out.ascii. The s.out.eOQ program is designed to create an ARC/INFO E00 ASCII points file. Alternatively, point data can be converted to raster data by s.to.rast and exported to ARC/INFO ASCII GRID by r.out.arc or other GIS raster formats.

Chapter 5

WORKING WITH RASTER DATA

In this chapter we explain the processing of raster data within GRASS, including some examples of spatial analysis. The raster data model, especially when combined with map algebra, provides wide range of capabilities for spatial modeling, all of which would be impossible to cover within a single chapter. Therefore, this chapter provides the basic description of the tools; more can be learned from the manual pages, tutorials and publications provided on

the GRASS Web site.

For a description of the GRASS raster data model, as well as raster data import and export, please refer to Section 4.1.3.

5.1. VIEWING AND MANAGING RASTER MAP LAYERS

In this section we continue to use the Spearfish data set to illustrate our examples. Please refer to Section 3.1.3 on how to start GRASS with the Spearfish LOCATION.

5.1.1 Displaying raster data and assigning a color table

Raster map layers can be displayed using the d.rast module. First open the GRASS monitor, then run the display module:

d.mon xO

d.rast elevation.dem

The map will be displayed in the GRASS monitor. The module d.rast offers two useful optional parameters, catlist and vallist. When us-