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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B4, 2012 
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia 
After these steps the user can populate the database with data and 
start using it. Compiling from source may take a long time mainly 
because the user has to gather appropriate versions of all the nec- 
essary libraries and make sure that the resulting environment is 
sound for entering production. The faster approach is to use an 
alternate source like ppa:sharpie/postgis — nightly (this works for 
Ubuntu Server), but such sources available at this time are clearly 
marked as unstable. 
PostGIS 2.0 can be installed on an existing database using the 
same procedures (it is recommended that any changes - related or 
not to PostGIS - to a production database are first validated on a 
testing environment). 
12 Usage 
Let us consider the following questions an Environmental Foren- 
sics expert in the Brazilian Federal Police might need answered: 
e Is the deforested area in a national park? 
e How far is the nearest water body from the landfill? 
e When was this area deforested? 
* Does this person have a mining permit for extracting gold in 
this part of the river? 
* Have any forensic reports ever been produced near this area? 
Let us also consider a hypothetical PostgreSQL 9.1/PostGIS 2.0 
database containing the tables used in the examples populated 
with the correct information. 
For the first question, the following example query would list all 
the national parks that intersect with that area and output the ac- 
tual overlapping area: 
SELECT name,ST_Intersection(geom,deforested_area) 
FROM protected_areas. national parks 
WHERE ST Intersects(geom,deforested area); 
For the next question, this is how we would find the distance in 
meters, the name and the geometry of the N nearest water bodies: 
SELECT 
name, 
ST Distance(geom: :geography, 
landfill geom: :geography) as distance, 
geom 
FROM physical maps.water bodies 
ÜRDER BY distance ASC NULLS LAST 
LIMIT N; 
The third question may not be directly answerable using only a 
query, but we may search the image footprint database for satel- 
lite Images of the area for visual inspection: 
SELECT id,date,download_path,geom 
FROM Satellite images.image catalog 
WHERE ST Intersects(geom,deforested area) ; 
Another alternative would be to use the new raster extension in 
PostGIS 2.0 for querying the satellite images directly and return- 
ing just the part of the images that overlap the area of interest. 
The other two questions could be answered in a similar way. 
These examples demonstrate what kind of usage a spatially en- 
abled database could be put to. End users would not make this 
kind of database access, but these queries could be run on the 
background by an application. 
2 POSTGIS 2.0 FEATURE HIGHLIGHTS 
PostGIS 2.0 has several new features and improvements from ver- 
sion 1.5.3. Some of these features are very interesting from a 
database maintenance but these stand out from the rest. 
2.1 Fixing invalid geometries 
The new function ST. MakeValid tries to automatically produce a 
valid version of invalid geometries without losing vertices. This 
operation does not work with all possible invalid geometries, but 
it tries to salvage as much as possible. That functionality is im- 
portant for Inteligeo because the data in the system is produced by 
third parties and arrives with very low quality control. ST. MakeValid 
provides an alternative to discarding invalid geometries from the 
Source data. 
The new function ST_IsValidDetail can be of great help if one 
tries to correct the data manually because it provides details on 
the reason for the invalidity and the precise location of the viola- 
tion. That can help a GIS analyst to be more efficient at correcting 
inconsistencies. 
3 
   
4 
(a) Invalid “bowtie” polygon (b) Topologically correct version 
Figure 1: Invalid geometry before and after correction with 
ST_MakeValid 
Figure la displays the graphical representation of the polygon 
defined in the WKT form POLYGON((-1 0, 1 0, 0 1, 0 -1, - 
1 0)), which is considered to be topologically invalid (section 
4.3.5 of [5]) because it self-intersects. Another issue with this 
geometry is that vertices have to be traversed in the clockwise 
order for the boundaries of polygons and counter-clockwise for 
the holes inside polygons. The implications of this are immedi- 
ately perceived when we try to calculate the area of such polygon: 
ST.Area of the geometry in Figure la yields 0 (zero area). The 
same operation applied on the geometry generated by ST. MakeValid 
on Figure 1b produces the correct area of 1. That geometry can 
be represented in WKT as MULTIPOLYGON(((-1 0, 0 0, 0 -1, 
-1 0)),((0 0, 0 1, 1 0, 0 0))). 
Other geometrical operations also produce unexpected results when 
applied to invalid geometries; Figure 2 displays the result of buffer- 
ing (ST-Buffer) the geometries in Figure 2.