3D Roof Modeling

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Plotting Roof-Planes for 3D-Building Modeling.

Introduction:

This document briefs the process of plotting the roof planes for the 3D Modeling of Buildings. A

small mistake in the beginning leads to a huge collective error. The final error may be crossing

of polygons, formation of several sliver polygons, open polygons (Unclosed) etc. The user is

supposed to follow certain systematic and logical steps to produce the best possible data.

Plane: A plane is a flat 2-dimentional surface which can be horizontal or slanted. Vertical planes

in 3D Roof-modeling are ignored because when they are projected vertically on ground. They

remain a line.

Edge: An edge is a line segment joining two adjacent vertices in a polygon.

Ridge: Ridge is the line that is formed when 2 planes intersect. It is a very important feature in

3D roof modeling because, more the number of ridges, more complex is the building.

Western Buildings:

Unlike Eastern Buildings, western building roofs are usually slanted. It does not allow accumulating snow

on the roof top.

(Fig-1 shows the multiple slanted roof planes)


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Process of plotting the roof planes:

1) Counting the number of planes of the roof and numbering them:

There is every possibility that unintentionally a roof plane may be missed in a complex building.

So the first step should be counting the number of planes the roof consists of and place the

numeric texts on each plane.

(Fig-2 Shows an example where this particular building has 30 planes\slants and is classified as a

complex building)


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2) Insert Orthogonal Corner Tool:

Most of the buildings are constructed with orthogonal corners. And it is advised to use Insert

Orthogonal Corner command. This command helps the user plot the sides of a polygon

orthogonally.

3) Observing the base-line:

Base-line is the longest side of the polygon plotted first. The whole Group of polygons depend

on the first polygon plotted because all the sides of the polygons are either parallel or

perpendicular to that polygon. Hence the base-line should be carefully plotted.

(Fig-3 shows the longer side of the first plotted polygon as base-line)


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4) Offsetting the parallel and perpendicular edges\ridges:

Use the Insert Parallel Line command to offset the portion of the polygon plotted first to the

sides of rest of the planes. This process helps prepare an accurate Engineering frame rather than

manual compilation with errors.

The important thing to remember is that all the parallel and perpendicular lines are plotted

using a temporary layer, say Layer-81.

(Picture-4 shows 2 sides of the base-polygon are offset to all the parallel and perpendicular edges and

ridges)


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5) Use of Batch Node tool:

Upon running Batch Node, it creates nodes (2D) where ever 2 lines intersect (2D or 3D). This

process creates polygons and helps the user to plot the planes by snapping each node.

(Fig-5 shows the batch application tool. The 2 things that must be taken care of while running

this application are; the Break Mode is set to Node only and the Z-Rule is set to Original

Elevations.)

By setting the Z-Rule as Original Elevations, the nodes are formed on the original line at the

same elevation.


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6) Plotting the irregular ridges:

For better quality, the irregular ridges are plotted afterplotting the orthogonal edges and

ridges. Once all orthogonal edges and ridges are plotted, it is easy to plot the irregular ridges.

(Fig-6 shows the irregular ridges plotted in a different layer with green pen)


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7) Plotting the planes one by one:

Now it is very simple and quick to plot each and every plane of the roof.

(Fig-7 and 8. To plot the building polygons a different layer is used with a special graphic pointer\font

that has tick marks. The clockwise compilation makes the tick-marks point inside of the polygons. In

other words, the tick-mark pointing inwards confirms that the polygon is plotted clockwise)

Note: In case any operator plots the building anti-clockwise, the ticks would point awayfrom the line

indicating the error which can then be rectified immediately.


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8) Use of Batch Direction tool:

In the group of polygons, every polygon must be plotted clockwise. A polygon with a counter

clockwise direction logically shows a hole\courtyard in the building roof. To avoid any human

error, Batch Direction

tool is used.

(Fig-9. This batch tool either makes all closed polygons clockwise or anticlockwise as assigned by

the user. Lets say the closed polygons layers are in Layer-127.

9) Deleting the temporary frame layers and removing the graphic pointers:

There is no need of the temporary engineering frame lines and fonts. They can be deleted.

(Fig-10)


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10) Using Line Cross Application.

In the process of compilation, unintentional human errors are inevitable. An improper snap may

lead to crossing of 2 polygons. Two crossed polygons create sliver polygons which is not what is

needed. Line Cross Batch Application helps count the number of line crossings and then drives

the user to each of the crossing lines for repair.

(Fig-11)

(Fig-12 In this case the application counts and displays zero crossing lines. The display can be

seen at the top bar.)


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11) Using Line Close Application:

This is the final step where a batch application Line Close is used to filter if the group of

polygons contains any unclosed polygon. The application counts the error polygons and drives

the user to each of them for repair.

(Fig-13 )

(Fig-14. For this case the batch application shows zero unclosed polygons)


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Some Examples:


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For further information or feedback or suggestions, please feel free to

contact,

Srikant PandaManager(Photogrammetry & LiDAR)

Geo Resource Mapping

[email protected]@gmail.com

www.geomapres.comFlat # 2, ShreeShailya Apartments,

Prabhat Road, Lane 14 (Income tax Lane)

Erandawane,Pune: 411004Skype :srikant.geod

Tel: 25431673/83Cell: +91 9370740737

3D Roof Modeling

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