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Docum mentation: Caren-Maria C Jörß 18.12.2011 / Englissh: August 2012 2

Volum meRend dering (Freak ( C Client V1) V Develo oper: Chris stian Tonn n

1. Introduction – the aim ms of Vol umeRend dering To visua alize volume measurem ments (for e example fro om ultrasoun nd tomograaphy, radar measurrements or building b phy ysics simula ations), a vo olume rende erer was im mplemented in the first FREAK software frramework. Volume V ren dering is an n establishe ed set of tecchniques for visualizing g large vo olume data sets. The novel aspectt of the conceived approach lies inn the combined visualisa ation of diffe erent resultts and the a ability to eva aluate them interactive ly in the con ntext of a digital b building mod del (overlay y). In this co ontext volum me rendering g is especiaally useful fo or making itt possible e to represe ent several volume v mea asurements s and other image-prodducing mea asurement methods in a single e model and d to overlayy these with h the model to provide pplanners wiith better information about the t building model.

2. Use er interfac ce

Fig. 1 VolumeRen ndering user interface Main window: Right sidebar:

ctive view Perspec GLSL sh hader param meters

3. Tuto orial In this tu utorial, we will w overlay a 3D mode el of a house e with volum me data from m a luminan nce calculattion, and subsequently adjust the value range e of the volu ume and exxamine diffe erent presenttation varian nts. Volume eRendering can acceptt data in the e following ffile formats: DAT, CSV, DZT and DAT+PAR R (read in different d ban nds next to each other)). 1. Beg gin by startin ng ServerFo our. 2. Load the 3D model of the house (“LK KG_Radiositty_x64.dbk””). 3. Oncce the data has loaded, start Volum meRenderin ng and connect to the server using the “@” button. 4. Load the volum me data for the t luminan nce calculation via the “File” “ menuu (“LK KG_Volume_66_128_5 58.dat”). For eacch volume data set thatt is loaded, a shader will w be create ed with the respective file f name in n can be set for each sh the relevant sub-m menu with wh hich the pre esentation parameters p hader. If the e imported data is no ot located at the correcct position, its position can c be shiftted using th he “Location n” function n in the resp pective volume’s menu u (Shader 1 “LKG_Vlou ume_66_1288_58.dat”).

3D model with w overlaid d volume off a luminanc ce calculatio on Fig. 2 3

3.1. Ad djusting th he value ra ange After the e data has been loaded, the corre ect value range for the volume neeeds to be se et. Without this it m may be difficcult to differe entiate the d different vallues in the rendered r di splay. The following example e shows the e luminance e distributio n within a building. b Bec cause the ra range of lum minance also o encomp passes the space s outside, the valu ue range is very large and a needs tto be adjusted to the

conditio ons within th he room. Th his adjustme ent makes it possible to o visually d ifferentiate the values in the interior. 1. Swittch to the 3D view of th he interior o of the buildin ng. 2. In th he volume’ss menu, clic ck on the “C Color” param meter. 3. In th he diagram that appearrs, the data a of the volume are sho own in grey with the minimum and maxximum value es shown beneath it. C Change the colour mod de from “lineear” to “RGB B” in the drop pdown abovve the diagrram. The vo olume value es in the 3D view now sshow in colo our. One ca an see that the lum minance vallues in the iinterior are mostly in th he red rangee. 4. To m make the luminance va alues in the interior eas sier to differrentiate usinng colours, the values in mmand” on the red range need n to be scaled. s Clic k on the volume menu: under “sum ne can add and subtract da ata and und der “factor” o one can mu ultiply the va alues. In RG GB mode we can see that red range lies l mostly in the first t hird of the value v range e. The valuees in the red d curve are also o those that are mostly in the interrior. To mak ke this data to extend aacross the whole w specctrum of the e RGB rang ge, a factor of 3.0000 needs n to be set.

Luminance an interior (RGB ( mode e) Fig. 3 L

Fig. F 4 Adap pted luminannce value ra ange

3.2. Crreating a section s thrrough the model In this ssection, we will cut a se ection throu ugh the 3D building b model and lum minance volume model so that we can look in nto the interiior from outtside. 1. We begin by cu utting the 3D D building m model. To see just the building moodel we switch off the visib bility of the volume v mod del (Parame eter “show”” = 0 in the volume’s v m enu). 2. In th he tree men nu under “Model clippin ng”, switch the t option “Use clippingg?” to 1. 3. To ccut a vertica al section th hrough the b building, we e need to sh hift a y-clippping axis. Se et the value e “min n-y” to 3.000 00. The 3D model will tthen be displayed betw ween the m inimum and d maximum clipp ping axes. The T parts off the model outside the ese limits will not be shhown. 4. The volume mo odel is clipp ped in the sa ame way us sing “Min Max” in the vvolume’s me enu. Here to oo, the “min-y” is set to 3.0000 0.

Fig. 5 C Cross section

3.3. Pre esentation n variants s (shaders s) The volume model can be ren ndered using g different shaders s to show s the voolume data in different ways. Click on n the volume e menu (Sh hader 1 “LK KG_Volume_ _66_128_58.dat”) to reeveal the re elevant parame eters. The “ssum shaderr” is set as d default. By dragging d the slider, diffferent types s of shaderss can be a activated.

3.3.1. s sum shade er Using th his shader, the results of each passs are adde ed and the sum s presennted. The co olours can be b changed d using the “Color” opttion in the vvolume’s me enu (see the e section beelow on “changing the colour o of the value range”).

Fig. 6 ssum shaderr presentatiion

3.3.2. m max shade er With this shader, only o the max ximum data a values of each pass are presenteed.

Fig. 7 m max shaderr presentatiion

3.3.3. s surface sh hader

This sha ader is bestt used for re evealing the e extents off volume data as it prodduces a surrface for a given th hreshold vallue in each pass. In thiis case, the presentatio on is made clearer by switching s th he “Color” mode from “RGB” back to “linear””. The boundary surfac ce is then shhown in grayscale. Using “Surface e” menu, pa arameters can c be adjussted that de etermine the e presentat ion of the boundary b surface. The param meter “borde er density”, for example, changes the precisioon of the su urface. Othe er parame eters include e lighting pa arameters (““ambient”, “diffuse”, “ “sp pecular”), thhe surface colour c and the t alpha va alue. The direction of the light can n be defined d using the “Light” optioon in the vo olume’s men nu.

ader presen ntation Fig. 8 ssurface sha

Fig. F 9 … aft fter changingg the borde er density

3.3.4. ttransp. surface As with the “surfacce shader”, this t shader creates a boundary b su urface but thhis time it is s transparen nt. The settting of the parameters is similar to p o those of th he surface shader. s

urface shade er presenta tion Fig. 10 transp. su

3.3.5. c cuts shade er The “cuts shader” places p a lon ngitudinal a nd a cross--section thro ough the voolume data and a only the e section through the e volume da ata is visible e. The parameters of th his shader aare mostly defined d in th he volume menu optio on “Cuts”. Here H one ca n set the po osition and visibility of tthe surface e of the x or y cross se ection. The axes can be b shifted byy dragging the t “cut x/y position” sllider. A secttion can be deactiva ated entirelyy by draggin ng the “cut x/y used?” slider from 1 to 0.

Fig. 11 cuts shade er Darstellun ng

3.3.6. ttrans. +op pak The “tra ans. +opak shader” s pro oduces an o opaque and a transpare ent bounda ry area at th he same tim me. As with the “surfacce shader”, the t colour m mode is bes st set to “line ear” (“Colorr” option in the t volume’’s menu). The precisiion of the bo oundary su rface can be defined using the “Suurface” optiion in the volume’’s menu. Th he paramete er “border d density” con ntrols the op paque boun dary surfac ce while “border density2” controls c the transparen nt boundary surface.

Fig. 12 trans. +op pak shader presentation p n

3.3.7. c cloud The “clo oud shader”” behaves much m like th he “sum sha ader” and also takes intto account the lighting conditio ons.

der presenttation Fig. 13 cloud shad

In the re espective vo olume’s me enu, there a re further options for controlling thhe presenta ation, which mostly cconcern the e lighting: “color fie eld mode”: A value of 0 means the e intensity of o light shou uld be show wn at every point in the e room. A value of 1 means the colour of th he light should be show wn at every point in the e room. “color adaption”: Whether W the brightness should be adjusted a to the surrounnding situation. “color normalize”: The T brightne ess is appli ed normaliz zed to the volume v (coloours are dis splayed normallyy).

3.4. Ch hanging th he colour of o the valu ue range (Color) ( How the e data is tra anslated into o a colour re epresentation can be defined d usinng the “Colo or” option in n the resp pective volu ume’s menu u. The defau ult setting is s “linear”. Otther colour presets can n, however,, also be selected, fo or example “inverse”, ““RGB” or “B BGR”. New colour c scheemes can be e created using th he buttons “New” and “Rename”. B By shifting the t splines at their “conntrol points””, the colourr values ccan be chan nges. Right-clicking on n a spline ad dds a new control c poin t and doublle-clicking on o the poin nt removes it. The “Spline” button switches be etween a cu urved and liinear presentation of th he lines. In the co olour bar be eneath the graph, g one sees the de efined colou urs of the vaalue range. Using the buttons “red”, “gree en”, “blue”, and “alpha”” the respec ctive control points cann be switche ed on and off. o The “alp pha” value controls c the e transparen ncy of the colours. By creating c andd shifting se everal contrrol points o on the blackk “alpha” line e, different degrees of transparency within thhe colour range are possible e.

Fig. 14 cuts shade er: RGB pre esentation

GB presenttation Fig. F 15 cuts s shader: RG

3.5. Ov verlaying two t volum mes (cond ition) In the V VolumeRend dering client, two differrent sets of volume data can be ovverlaid. How w these two o volumess interact with w one ano other can be e controlled using the “Condition” ooption of the respective volume.. For examp ple, one cou uld specify tthat the first volume will only be shhown in tho ose points where the two volu umes overla ap when the e value rang ge for the se econd volum me fulfils ce ertain conditio ons. With the e first param meter, we de efine the kin nd of condittion:

“no condition” : no condition will apply “other volume”: the value of the other volume applies “volume sum”: the sum of the volume values at a point in space applies “volume product”: the product of the volume values at a point in space applies The second parameter: “out of range value”: is used as a value in those points where the two volumes do not overlap. Further parameters: One can define three different ranges (“range 1-3”). When the volume values lie outside these predefined ranges, they will not be displayed. Within the range, the volume is visible. Whether a range should be applied or not is controlled using the function “use range 1-3” (0 = no, 1 = yes).

Volume Rendering Tutorial  

Volume Rendering Tutorial