meta-data

After some search, it seems that Google Earth uses 90M SRTM data set (NASA Shuttle Radar Topography Mission).
Here is post I found:
http://bbs.keyhole.com/ubb/showflat.php/Cat/0/Number/397432/an/0/page/0/vc/1
here is the data page:
http://edc.usgs.gov/srtm/data/obtainingdata.html

There are other available DEM data of difference resolutions and coverage areas as well

http://edc.usgs.gov/products/elevation/gtopo30/gtopo30.html
http://www.ngdc.noaa.gov/mgg/topo/gltiles.html
http://www.mapmart.com/module/DEM.htm

The last one has the highest resolution, and its elevation data is free of charge (need to submit a purchase of 0 dollar)

And here is the tool for Google Earth to integrate geospatial data:
http://earth.google.com/earth_fusion.html

raster data format

General d-dimensional raster formats are used for spatio-temporal or multispectral data (e.g. HDF format).

vector data format

multiple layers

The multipurpose GIS usually stores the georeferenced data as thematic map layers. Each geographic feature or theme, such as streams, roads, vegetation or cities is stored in a separate map layer using the vector or raster data model. The map layers can then be combined to create different types of new maps as well as perform analysis of spatial relations.

data organization

GRASS data are stored in a UNIX directory referred to as DATABASE (also called “GISDBASE”). This directory has to be created with mkdir or a file manager, before starting to work with GRASS. Within this DATABASE, the projects are organized by project areas stored in subdirectories called LOCATIONS. A LOCATION is defined by its coordinate system, map projection and geographical boundaries. The subdirectories and files defining a LOCATION are created automatically when GRASS is started the first time with a new LOCATION. Each LOCATION can have several MAPSETs. One motivation to maintain different mapsets is to store maps related to project issues or subregions.

module

GRASS modules are organized by name, based on their function class (display, general, imagery, raster, vector or site, etc.) The first letter refers to the function class, followedby a dot and one or two other words, again separated by dots, describing the specific task performed by the module.

d.* display graphical output

s.* sites site data processing

r.* raster raster data processing

i.* imagery image processing

v.* vector vector data processing

g.* general general file operations

m.* misc miscellaneous commands

p.* paint map creation in PPM format

ps.* postscript map creation in Postscript format

—————-

g.list rast

g.list vect

g.list sites

——————

r.info soils

v.info streams

s.info archsites

——————-

open a GRASS monitor

d.mon x0

(only x0 to x6 can be opened)

d.rast soils

d.vect streams col=blue

d.sites archsites col=white type=box

—————

check the definition of your LOCATION:

g.proj -p

g.region -p

g.region -m

———————–

Coordinate system transformations

Geospatial data for a given study area are often provided in different coordinate systems (UTM, State Plane and geographic coordinates).

To transform data between different projections and coordinate systems.

For example, to transform the corner points of the Spearfish LOCATION from UTM/Clark66/NAD27 to latitude-longitude/WGS84:

cs2cs -v +proj=utm +zone=13 +ellps=clrk66 +datum=NAD27 \

+units=m +to +proj=latlong

Entering for example the north/west map corner of the Spearfish LOCATION delivers:

589980 4928010

103d52′7.399”W 44d30′6.293”N 0.000

which represents the corresponding latitude-longitude/WGS84 coordinates.

— As other example, we transform coordinates from UTM/Clark66/NAD27 to LAEA/Sphere/no datum. We will store the values in a file:

1. start GRASS with the Spearfish LOCATION and run:

g.region -pd

2. put the reported values in a file spearfishUTM_NAD27.txt

3. convert the coordinates in the file to the standard raster map projection of the National Atlas of the U.S., which is Lambert Azimuthal Equal Area (LAEA) on a sphere:

cat spearfishUTM_NAD27.txt | cs2cs -v +proj=utm +zone=13 \

+ellps=clrk66 +datum=NAD27 +units=m +to \

+proj=laea +lat_0=45 +lon_0=-100 +x_0=0 +y_0=0 +ellps=sphere \

+units=m > spearfishLAEA.txt

the output will look like:

-306676.27 -48094.86 0.00

-287744.36 -49261.79 0.00

-288620.30 -63563.34 0.00

-307552.56 -62397.59 0.00

more on projection later

———————————————————

DATA MODELS and DATA EXCHANGE

Raster map layer is stored in GRASS as a set of files, which include the raster data and their description:

• generic matrix of values in a compressed format which depends on the raster data type
• map header which contains georeferencing data, resolution, number of rows and columns, range of values and histogram
• optional category file which contains text or numeric labels
• optional color table
• optional timestamp
• history file which contains metadata such as the data source or other informaton provided by the user.
• reclass table for a map that is a reclassification of another map.

g.region res=12.5                           will set the resolution to 12.5 map units (e.g. meters)

g.region rast=elevation.dem -p     define region from existing map according to elevation.dem

g.region -dp                                      reset the region to the default region of the LOCATION