GIS Mystery Cache

[CZ]

[EN]

[CZ]

Na zadanych souradnicich cache nehledejte!

Geograficke Informacni Systemy

GIS je jakykoliv manualne nebo pocitacove zalozeny soubor postupu uzivanych k ukladani a manipulovani geograficky vztaznych dat.
Geograficky vztazena data maji dve slozky:

• fyzikalni rozmer respektive tridu (pocet obyvatel mesta, typ sidla, typ vegetace atd.)
• prostorovou lokalizaci ve vztahu ke zvolenemu souradnemu systemu (polarni souradnice, souradnice ve zvolenem systemy kartografickeho zobrazeni)

Za geograficky informacni system povazujeme pocitacove orientovany informacni system, ktery pracuje se geograficky vztazenymi daty, ktera maji tyto dve slozky (popisnou / prostorovou (lokacni)) a ktery umoznuje:

• vstup techto dat
• spravu (management) dat
• manipulaci s daty a analyzu dat
• vystup dat

Na samotny GIS se muzeme divat jako na obvykly informacni system, doplneny o funkcnost vztahujici se k prostorovym datum, aby bylo mozne pokladat i prostorove dotazy. Tedy aby bylo mozne zjistovat nejen "kdo vlastni parcelu" nebo "jake parcely vlastni osoba" (dotazy na popisna data), ale take "kde se nachazi parcela", "ktere parcely sousedi s touto parcelou", "jake inzenyrske site prochazi parcelou" a podobne (dotazy na prostorova data).

Samotne ulozeni prostorovych dat je realizovano 2 hlavnimy zpusoby:

• vektorova data - reprezentuji objekty pomoci datovych struktur, jejichz zakladni polozkou je bod dvourozmerneho, spojiteho (euklidovskeho) prostoru. Objekty v prostoru mohou byt 3 typu: bod, lomena cara (linie) a oblast (areal).
• rastrova data - tvori podmnozinu 2D prostoru, pravidelne rozdelenou (obvykle ctvercovou) siti. Kazdy element (ctverec) teto site je nositelem tematicke casti (geograficke) informace. Prostorova lokalizace je urcena indexem elementarni slozky site, pripadne jeho zobrazenim do ciloheho souradneho systemu. Typickym prikladem takovych dat jsou snimky ze satelitu (pocasi) ci skenovane mapy. U rastrovych dat je tematicka cast informace ziskavana zaroven s casti lokalizacni.

Dalsi nezbytnou informaci je topologie. Ta vymezuje vztahy mezi entitami (objekty) systemu, aniz by obsahovala umisteni objektu v prostoru. Napriklad informacni system o spojeni mist silnicni site nevyzaduje presne umisteni uzlu v prostoru, ale pracuje pouze s relacemi na mnozine vsech uzlu.
Velmi casto se topologicke vztahy pouzivaji ve spojeni s vektorovou reprezentaci prostorovych dat.

Vsechno zatim vypada velmi jednoduse, ovsem praxe je podstatne obtiznejsi a musi resit ulohy typu jak zjistit vzdalenost bodu od linie / polygonu, jak zjistit ze bod lezi v polygonu, pruniky polygonu, topologicke ulohy pro distribucni site elektriny, kanalizace atd.

Aby vubec bylo mozne efektivne pracovat s prostorovymi daty, je potreba je se rychle orientovat v prostoru. Jinymi slovy GIS musi reagovat na dotazy typu co je v oblasti. Efektivni pristupove metody jsou dulezite hlavne u vektorovych dat a ve sve podstate se nelisi od tradicnich rozsahovych vyhledavacich problemu, komplikaci je vsak vice dimenzi. Tradicni "jednorozmerne" techniky vice dimenzi nezvladaji, proto byly vyvinuty specialni vicedimenzionalni vyhledavaci algoritmy (R-Tree, Quad Tree, k-D stromy (k-dimensionalni), Grid,..). Pristupove metody pro praci s rastrove reprezentovanymi daty jsou jednodussi, jedna se vetsinou o primou adresaci v ramci prislusneho souboru.

Velmi uzitecnym zdrojem informaci a dat je Cesky urad zememericsky a katastralni, ktery ma na starosti spravu katastru nemovitosti, statni mapove dilo a take Zabaged (R) - ZAkladni BAze GEografickych Dat).

Pokud si sami chcete vyzkouset ukladani a praci s prostorovymi daty v DB, muzete zdarma vyzkouset Oracle Database Express Edition (Oracle Database XE) s podporou Oracle Locator.

Ukoly

V meritku 1:2880 je ctverec o strane 40 sahu (dolnorakouske jitro) zobrazen jako ctverecnm palec.
Jedna stopa ma 12 palcu. Sah se sklada ze stop.
Kolik stop obsahuje jeden sah?
(neni potreba nic hledat, staci pocitat)
1 sah = A stop

Kolik porovnani (minimalni) je potreba v podmince urcujici zda se prekryvaji dva 2D obdelniky se stranami rovnobeznymi s osami x, y.
(hint: O1=[xmin1,ymin1,xmax1,ymax1], O2=[xmin2,ymin2,xmax2,ymax2])
a) 4 (B=4)
b) 16 (B=2)
c) 64 (B=8)
d) 128 (B=6)

Jestlize Vinnetou mluvil o 5 akrech pozemku pro bileho bratra, kolik metru ctverecnich mel na mysli (zaokrouhleno)?
a) 12 000 m² (C=7)
b) 20 250 m² (C=8)
c) 25 000 m² (C=9)

Sousedi listy zakladnich map CR 24-44-23 a 34-22-03?
a) ano (D=1)
b) ne, je mezi nimi jeden dalsi mapovy list (D=2)
b) ne (D=3)

Umisteni

Cache je umistena na N 49º 12.AB7 E 016º 39.CD1

Pri vyzvedavani budte velmi opatrni, spis nez na mudly z obchody si davejte pozor na mudly v prilehle budove.
Keska je absolutni drive-in, mozna by se dala ulovit bez vystoupeni z auta, ale to by budilo pozornost. Klidne si prectete hint a v ramci kamuflaze se kochejte vyhledem, stoji za to.

[EN]

The cache is not on the initial coordinates!

Geographic Information Systems

GIS is manual or computer based set of processes used for saving and manipulating geographically referenced information.
Geographic referential datas consists of two elements:

• physical feature or (if you like) class (city population, domicile class, vegetation class etc.)
• spatial location in relation to selected system of coordinates (polar coordinates etc.)

Computer oriented information system is rated as geohraphic information system, if works with geographically referenced information with those two (descriptive / spatial) elements and allows:

• input of spatial information
• management of spatial information
• spatial data manipulation and analysis
• spatial data output

You can look at GIS as on normal information systems, with added geographical data functionality to answer spatial queries. This give the possibility to investigate "who own this building estate" or "which plots are owned by this person" (descriptive data query), but also "where is this this building estate", "which building estates are neigbouring to this one", "which elektricity lines and pipes go thru this plot" etc. (spatial data query).

The storage of spatial data can be done in two main ways:

• vector - represents object as data structure which basic element is point in twodimensional, coherent (euklid) space. Object in this space can be one of 3 types: point, open polygon (line) and area.
• raster - subset of 2D space, periodically divided (usualy quadrate) net. Each element (square) of this net is bearer of thematical part (geographical) information. Spatial location is determined by register of elementary components of the network, eventualy by its presentation in target coordinates system. Typical examples are images made by satelite (weather) or scanned maps. Thematical part of information is obtained simultaneously with location.

Other necessary information is also topology. Without any information about location of objects in space, it makes relations between system entities (objects) without. For example road connection information system does not necessary contain any junction spatial data, but works just with relations on the set of all junctions.
Topological relations are very often used by vector data representation.

Everything to this point seems to be very easy, but the reality and work experience is much more hard and must answer queries like how to measuer the distance between point and line / polygon, or how to figure out if point is inside polygon / intersection of polygons, electricity / water distribution topological task etc.

To work with spatial data, it's necessary to gear quickly in the space. In other words, it must respond to queries like what is in this area. Efective access methods are very important primary to work with vector data and in its principle is not so different from traditional range searching problems, complications are just more dimensions. Traditional "one dimensional" techniques are uneffective on this problems, so new special multidimensional algorithms were developed (R-Tree, Quad Tree, k-D Trees (k-dimensional), Grid...). Accessing methods for work with raster represented data are easier: it is just direct addressation in relevant file.

Useful source of informations and datas is Cesky urad zememericsky a katastralni (Czech Office For Surveying, Mapping And Cadastre), which administrate the Cadastre (including legal relations to real estate property), CR State maps and also Zabaged (R) - Fundamental Base of Geographic Data, DMU25 - digital map administrated by army cartography.

You can try database work with spatial data on your own for free on Oracle Database Express Edition (Oracle Database XE) with Oracle Locator functionality.

Questions

Using a scale of 1:2880, a square, 40 fathoms by 40 fathoms, is displayed as one square inch.
We know that one foot is 12 inches. How many feet are in one fathom?
(No Googling is needed, just some simple math).
1 fathom = A foots

How many comparisons are needed to determine the incidence of two 2D rectangles with sides parallel to the x and y axes?
(hint: O1=[xmin1,ymin1,xmax1,ymax1], O2=[xmin2,ymin2,xmax2,ymax2])
a) 4 (B=4)
b) 16 (B=2)
c) 64 (B=8)
d) 128 (B=6)

It is said that Geronimo sold 5 acres of land to the white settlers in exchange for some shiny glass beads. How many square meters did Geronimo sell? (rounded)
a) 12 000 m² (C=7)
b) 20 250 m² (C=8)
c) 25 000 m² (C=9)

Consider sheets 24-44-23 and 34-22-03 of the CR base maps. Are these two sheets side-by-side neighbors?
a) yes (D=1)
b) no, one map sheet between them (D=2)
b) no (D=3)

Location

Cache is at the following coordinates N 49º 12.AB7 E 016º 39.CD1

Be very careful - especially watch muggles from nearby building. It is an absolute drive-in cache, it could be possible even to grab the cache without exitting the car but doing so would be very suspicious. Don't worry, read the hint and cover your behavior by admiring the view, it is worth it.