Tuesday, 12 December 2017

Lab experiment - 3D reconstruction of a masonry wall

Siyuan Chen
Time: 2017
Location: Dublin

As we know, photogrammetry methods like structure from motion (SFM) has the potential to generate 3D models or point cloud from 2D imagery data. Combined with UAVs, this method can provide a significant help for civil engineers in rapid modeling. The usage scenario could be urban modeling, post-disaster survey and construction site inspection. To have a better understanding of the limitation of the method and related influence factors, a lab-based experiment has been conducted in UCD.

With the help from my colleagues Iman and Atteyeh, four masonry walls have been built in the lab. Both the Laser scanner and the digital camera have been applied for data collection. An adjustable tripod has used to control the camera angle and distance to the wall. The reconstruction process has been completed by the open source software VisualSFM. After a comparison, we figure out that the result is highly related to the images angles. The data completeness, density distribution and geometry accuracy are all related to the angle selection. More details have presented in the conference paper ‘The effect of angles and distance on image-based, three-dimensional reconstructions’- DOI10.1201/9781315210469-350. The final suggestion is that, in UAV inspection, it is much better to put the camara axis vertical to the target surface. And using muitipal flight path can improving the data completeness.

Siyuan Chen 
School of Civil, Structural and Environmental Engineering
University College Dublin, Ireland

Email:  siyuan.chen@ucd.ie

Thursday, 15 June 2017

Fly the drone above water - Floating base design for UAVs

Fly the drone above water - Floating base design for UAVs

Date: May 30, 2017
Location: Dublin

Using drones for photography and inspection have become more and more popular. In some situation,  such as recording the water sports or doing under bridge inspection, we have to fly the drone close to the water surface. It looks like an easy job,  but it is really a challenging for drone operators. The done should always keep a safe distance to the water surface, but the cross wind and waves will prevent the operator to do so. Even advanced drones are equipped with high-tech sensors, such as ultrasonic sensor, visual detector, barometer for altitude holding, they are not working well in an environment filled with random reflection and inconstant air flows.

Figure 1. Flying above the water

Figure 2. Floating base for UAVs

In our research, for under bridge inspection, we designed a cheap floating base to avoid water damage, shown in Figure 1 and Figure 2. The float base only includes a frame and four bottles and appropriate for different drones. In the field survey, it works well. If you are interested in it and want to make one for your ‘baby’, here are some tips:

1. Frame

The frame is used for connecting the drone and fixing bottles caps. You can use any light and solid materials (acrylic or aluminum) or any manufacturing method (machining or 3D printing), but remember to leave am empty areas below the camera and other sensors. In addition, make the angle between two front bottles bigger can further ensure the camera is unblocked. 

Figure 3. Frame design

2. Bottles

Theoretically, a 1L bottle can support 1kg's weight. Thus for a DJI Phantom 4 (about 2kg), 4x500ml bottles will be enough. But considering the momentum when the drone falls off and the possible deformation of plastic bottles, we used 4 1L bottles in our case.

Instead of installing the bottles vertical or horizontal,  we using a 30-degree angle to avoid the flip-over problem (vertical setting will have). It solved the inefficient aerodynamic problem and lower floating center problem (horizontal setting will have) as well.  If you are lucky to find some narrow neck bottles, the aerodynamic performance could be further improved.

Images of the test and field survey

Flight time and wind resistance test (20 min)

Weight and balance test (2.5 kg)

Under bridge survey

Siyuan Chen 
School of Civil, Structural and Environmental Engineering
University College Dublin, Ireland

Thursday, 20 October 2016

Drone Workshop in UCD

Drone Workshop in UCD

Date: September 29th, 2016
Location: Newstead, UCD

Unmanned aerial vehicles (UAVs) or Drones developed rapidly recently and drawn attentions from mass public. To help students get a close contact with drone technologies, last month in UCD, Dr Eleni Mangina arranged a workshop for graduate students. PhD student Even O'Keeffe and I made presentations during the workshop. Almost 20 students attended.

In the beginning, Dr Eleni Mangina introduced the history and current applications of UAVs.

After that, Even O'Keeffe explained the legal requirement for UAVs application in Ireland. He also shared his experience in drone-related software developing.

Then, I showed them the steps of building a DIY drone. Introduction to each component and tips for model selection also included.

In the last, students get a chance to have a close look at different drones and ask questions.


Siyuan Chen
School of Civil, Structural and Environmental Engineering
University College Dublin, Ireland

Thursday, 28 July 2016

Boyne Viaduct Bridge Aerial Survey

Boyne Viaduct Bridge Aerial Survey

Date: July 6th, 2016
Location: Boyne Viaduct Bridge
Completed by: Jonathan Byrne, Siyuan Chen


Boyne Viaduct Bridge is located in Drogheda, about 50 km north of Dublin city center. The viaduct is 30 meters high, comprises twelve stone arches on the south side, and a further three arches on the north. It was designed by the Irish civil engineer Sir John Benjamin Macneill, constructed in 1855, and refurbished in 2015.
Google Map

In the early morning, Jonathan and I inspected the south side with two flights.

Aerial Images


3D Reconstruction

3D reconstruction process was based on 287 aerial images and 321 ground images. Python Based platform VisualSFM[1], Commercial platform PhotoScanPro[2],  and open source platform Meshlab[3].

Aerial Video

In the last, let us enjoy a short aerial video.



Siyuan Chen
School of Civil, Structural and Environmental Engineering
University College Dublin, Ireland

[1] VisualSFM was created by Changchang Wu at the University of Washington Seattle.

[2] PhotoScanPro, developed by Agisoft, is a stand-alone software product that performs photogrammetric processing of digital images and generates 3D spatial data.

[3] MeshLab is an open source, portable, and extensible system for the processing and editing of unstructured 3D triangular meshes.

Tuesday, 26 July 2016

New Drone Test

New Drone Test

In last month, I started to build a new DIY drone. Some details will be attached below.

Drone Building

This drone we using an old Tarot 650 carbon fiber frame, 4 x kv800 rotors,4 x 12-inch propellers (4 x 15-inch propellers), 4 x 30-A ESCs, Pixhawk flight controller with 3DR GPS module, Turnigy 9xr pro radio controller with FrySKY XJT module, X8R SBUS receiver, and 3DR telemeter.

Drone Setting

APM Planner was used fro flight controller setting. RC was programmed by eepskye. 

After basic setting and sensors calibration, I went out for several times flight test. Here I can write a book named 'Drone accidents'. The first time, before took off, one propeller was loose and shoot off. The second time, it spinning on the ground and flipped over. The third time, it can take off, but direct crashed on a tree (One leg was gone). The fourth time crashed on a wall (Another leg was gone). The fifth time.....  (Sorry, too many times, it is hard to recall all of them.)

Every accident made the drone settings improved a little but made the physical structure damaged a lot. I do not want it to be totally destroyed before the successfully take off. So, after several days' hard repairing, I designed a few indoor test methods. 

Indoor Test

Four pipes were mounted on each arm to keep a safe distance for propellers. Steel core cord went through those pipes to restrict drone’s movement. In the video, you can see the drone flight just like an angry wasp. It was lucky I bought strong enough cords.

PID Tuning

To adjust the PID parameters for flight control. Two tables were used to fix the vertical movement of the drone. After several times test, with the help from Even, the PID curves are looks much better.


Outdoor Test

After got a satisfied setting, we did an outdoor test. Finally, it successfully took off and followed with a safe landing.   : D


Siyuan Chen
School of Civil, Structural and Environmental Engineering
University College Dublin, Ireland

Sunday, 10 July 2016

Events in past few months

Events in past few months

In last three months, lots of exciting things happened in Ireland about drones. Here, I will make a short record for those activities.

Drone Explore Ireland

From April 1st to 3rd, Drone Explore Ireland was holding in Dublin RDS. It was a carnival for drone lover. Different companies brought their most advanced products to the exhibition. Such as UAV platforms, camera, and sensors. Besides some manufacturing companies, aerial service companies also attracted people. Aerial survey, filmmaking, on-site inspection, and rescue are hot topics.

Other than products exhibition, I also enjoyed the drone racing and presentation parts. The officer from IAA (Irish Aviation Authority) made a presentation on new restriction about UAV application and registration in Ireland. Our postdoctoral researcher Jonathan Byrne introduced the current achievements from UCD urban modeling group


My Secondment in Arup

I started my secondment in Arup from April. In the following month, I made a presentation topic on UAV application. Almost 40 people  attended from Dublin branch and others were joined by Skype from other cities.

Aerial Survey for Boland's Mills

Boland's Mill is located on the Grand Canal Dock in Dublin, Ireland on Ringsend Road between the inner basin of Grand Canal Dock and Barrow Street. It is currently undergoing a €150 million reconstruction to become Boland's Quay, accommodating new residences, commercial, retail, and civic spaces. [1, 2]

Before the structures are torn down, UCD urban modelling group cooperated with Arup made an aerial survey to 3D reconstruct the historical building. 


3D Model [3]

[1] http://www.irishtimes.com/business/construction/green-light-for-150m-boland-s-mill-development-1.2271477
[2] https://en.wikipedia.org/wiki/Boland%27s_Mill
[3] Made by Jonathan Byrne from UCD urban modelling group.


Siyuan Chen
School of Civil, Structural and Environmental Engineering
University College Dublin, Ireland

Sunday, 28 February 2016

How to USE StackEdit and Markdown in Blog!

How to USE StackEdit and Markdown in Blog!

In my blog, I will introduce some handy tools or software which make my life easer. Those blogs will have the tag tool&skills. As I am using Markdown1 and StackEdit2 to deal with my blog publication. Here, I will first make a simple introduction about this two tools and some tricks.

About Markdown

Markdown is a lightweight markup language with plain text formatting syntax designed so that it can be converted to HTML and many other formats3. If you use Git a lot, you must know that it is used to format readme files.

Markdown Syntax:

Original Code will shows like this.
Result will shows like this.


Following by different numbers of ‘#’ you can get different level’s header.
# H1
## H2
### H3




Alternatively, for H1 and H2, an underline-ish style:





Emphasis, aka italics, with *asterisks* or _underscores_.

Strong emphasis, aka bold, with **asterisks** or __underscores__.

Combined emphasis with **asterisks and _underscores_**.

Strikethrough uses two tildes. ~~Scratch this.~~
Emphasis, aka italics, with asterisks or underscores.
Strong emphasis, aka bold, with asterisks or underscores.
Combined emphasis with asterisks and underscores.
Strikethrough uses two tildes.
Scratch this.
This is [an example](http://trussitn.eu/siyuan-chen/) inline link.

This is an example of link.


![Image name](http://trussitn.eu/wp-content/uploads/2015/02/logo-120h-v1.jpg)

[![Image with link](http://trussitn.eu/wp-content/uploads/2015/02/logo-120h-v1.jpg)](http://trussitn.eu/siyuan-chen/)
Image name
Image with link


You can create footnotes like this[^footnote].

  [^footnote]: Here is the *text* of the **footnote**.
You can create footnotes like this4.


Markdown Extra has a special syntax for tables:
Item     | Value
-------- | ---
Computer | $1600
Phone    | $12
Pipe     | $1
Item Value
Computer $1600
Phone $12
Pipe $1
You can specify column alignment with one or two colons:
| Item     | Value | Qty   |
| :------- | ----: | :---: |
| A        | $1    |  4    |
| B        | $2    |  5    |
| C        | $3    | 6     |
Item Value Qty
A $1 4
B $2 5
C $3 6

Table of contents

You can insert a table of contents using the marker [TOC] to auto insert the table of contents:

Math Expressions

You can use LaTeX 5 syntax for mathematical expressions:
The *Gamma function* satisfying $\Gamma(n) = (n-1)!\quad\forall n\in\mathbb N$ is via the Euler integral

\Gamma(z) = \int_0^\infty t^{z-1}e^{-t}dt\,.
The Gamma function satisfying Γ(n)=(n1)!nN is via the Euler integral


Note: You can find more information about LaTeX mathematical expressions here.

UML diagrams

You can also render sequence diagrams like this:
Alice->Bob: Hello Bob, how are you?
Note right of Bob: Bob thinks
Bob-->Alice: I am good thanks!```
Created with Raphaël 2.1.2AliceAliceBobBobHello Bob, how are you?Bob thinksI am good thanks!
Note: You can find more information:
  • about Sequence diagrams syntax here,
  • about Flow charts syntax here.

About StackEdit

StackEdit is a browser editor. All your documents are automatically saved locally and are accessible offline!. It can binding to your Google Drive or Dropbox account to synchronization your work to the cloud. It also provided a one key publication function to push your work to Blog account.

Create a document

The document panel is accessible using the button in the navigation bar. You can create a new document by clicking New document in the document panel.

Delete a document

You can delete the current document by clicking Delete document in the document panel.

Export a document

You can save the current document to a file by clicking Export to disk from the menu panel.
Tip: Check out the Publish a document section for a description of the different output formats.


StackEdit can be combined with Google Drive and Dropbox to have your documents saved in the Cloud. The synchronization mechanism takes care of uploading your modifications or downloading the latest version of your documents.


Once you are happy with your document, you can publish it on different websites directly from StackEdit. As for now, StackEdit can publish on Blogger, Dropbox, Gist, GitHub, Google Drive, Tumblr, WordPress and on any SSH server.


Siyuan Chen
School of Civil, Structural and Environmental Engineering
University College Dublin, Ireland

  1. Markdown is a lightweight markup language with plain text formatting syntax designed so that it can be converted to HTML and many other formats using a tool by the same name.
  2. StackEdit is a full-featured, open-source Markdown editor based on PageDown, the Markdown library used by Stack Overflow and the other Stack Exchange sites.
  3. https://en.wikipedia.org/wiki/Markdown
  4. Here is the text of the footnote.
  5. LaTeX is a high-quality typesetting system; it includes features designed for the production of technical and scientific documentation.