OSM Road Data Fails! - Githubissues

I use Space Syntax Toolkit in QGIS. I cut the road network I downloaded from the OSM website according to the city boundary. I am cleaning with RCL. However, when I try to segment analysis, the SST breaks the road data into small pieces. And as a result, analysis is not possible. Now I have a few questions for you: (My versions are: QGIS 2.18.14 and 2.18.28 + SST 0.2.1) 1- What should I go through after downloading the road data from OSM? 2- There is no problem in the axial maps I have drawn, but I need OSM data as I have to analyze the whole city. Which website are you downloading from? 3- Stages: 1- Import OSM data into QGIS. 2- Cut by city boundary. 3- Select snapping, load error and load unlinks with RCL (decimal 9). 4- Open the Open Graphs tab and add the cleaned road layer to the layer section. 5- Select the segment (n radius) and press the Calculate button. 6- And the faulty, fragmented road network comes out :)

The reason why your map is broken in many little segments is because in the original OSM data many roads are polylines consisting of many tiny segments (especially in roundabouts). In order to get rid of those segments, you need to simplify the polylines based on the angles their segments create, i.e. if two segments of the same polyline are almost collinear make them one straight line (Douglas-Peucker algorithm).

The latest development of the RCL tool includes the option to simplify such angular changes. You might need to adjust the threshold of the simplification - the bigger the threshold the cruder the simplification.

[image: Screenshot 2020-09-28 at 13.07.06.png]

After the cleaning of your OSM map, you should use the Network Segmenter to segment your map in QGIS. Then you can use the Graph analysis tool to run angular segment analysis and make sure you tick 'RCL or segment map'.

Please use the latest development version of the toolkit https://github.com/SpaceGroupUCL/qgisSpaceSyntaxToolkit/tree/development_v_0_3 , which you have to install manually following the instructions below.

Select Clone or download >Download ZIP and extract files from zipped folder.
Download the latest Plugin.zip file (top right corner of the page)
Unzip and copy (copy & replace) the entire folder into the QGIS plugins directory. This directory can be found here: Users/(your user name)/.qgis2/python/plugins/). This directory is usually hidden and you must make hidden files visible.

Hope this solves the issue.

Best,

Ioanna

Στις Δευ, 28 Σεπ 2020 στις 9:46 π.μ., ο/η haktank5 notifications@github.com έγραψε:

I use Space Syntax Toolkit in QGIS. I cut the road network I downloaded from the OSM website according to the city boundary. I am cleaning with RCL. However, when I try to segment analysis, the SST breaks the road data into small pieces. And as a result, analysis is not possible. Now I have a few questions for you: (My versions are: QGIS 2.18.14 and 2.18.28 + SST 0.2.1) 1- What should I go through after downloading the road data from OSM? 2- There is no problem in the axial maps I have drawn, but I need OSM data as I have to analyze the whole city. Which website are you downloading from? 3- Stages: 1- Import OSM data into QGIS. 2- Cut by city boundary. 3- Select snapping, load error and load unlinks with RCL (decimal 9). 4- Open the Open Graphs tab and add the cleaned road layer to the layer section. 5- Select the segment (n radius) and press the Calculate button. 6- And the faulty, fragmented road network comes out :)

— You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub https://github.com/SpaceGroupUCL/qgisSpaceSyntaxToolkit/issues/183, or unsubscribe https://github.com/notifications/unsubscribe-auth/ADLJBFFUNO7PGHWWTXTN253SIBENJANCNFSM4R4HIB3Q .

-- Ioanna Kolovou GIS analyst and developer

The reason why your map is broken in many little segments is because in the original OSM data many roads are polylines consisting of many tiny segments (especially in roundabouts). In order to get rid of those segments, you need to simplify the polylines based on the angles their segments create, i.e. if two segments of the same polyline are almost collinear make them one straight line (Douglas-Peucker algorithm). The latest development of the RCL tool includes the option to simplify such angular changes. You might need to adjust the threshold of the simplification - the bigger the threshold the cruder the simplification. [image: Screenshot 2020-09-28 at 13.07.06.png] After the cleaning of your OSM map, you should use the Network Segmenter to segment your map in QGIS. Then you can use the Graph analysis tool to run angular segment analysis and make sure you tick 'RCL or segment map'. Please use the latest development version of the toolkit https://github.com/SpaceGroupUCL/qgisSpaceSyntaxToolkit/tree/development_v_0_3 , which you have to install manually following the instructions below. - Select Clone or download >Download ZIP and extract files from zipped folder. - Download the latest Plugin.zip file (top right corner of the page) - Unzip and copy (copy & replace) the entire folder into the QGIS plugins directory. This directory can be found here: Users/(your user name)/.qgis2/python/plugins/). This directory is usually hidden and you must make hidden files visible. Hope this solves the issue. Best, Ioanna Στις Δευ, 28 Σεπ 2020 στις 9:46 π.μ., ο/η haktank5 notifications@github.com έγραψε: … I use Space Syntax Toolkit in QGIS. I cut the road network I downloaded from the OSM website according to the city boundary. I am cleaning with RCL. However, when I try to segment analysis, the SST breaks the road data into small pieces. And as a result, analysis is not possible. Now I have a few questions for you: (My versions are: QGIS 2.18.14 and 2.18.28 + SST 0.2.1) 1- What should I go through after downloading the road data from OSM? 2- There is no problem in the axial maps I have drawn, but I need OSM data as I have to analyze the whole city. Which website are you downloading from? 3- Stages: 1- Import OSM data into QGIS. 2- Cut by city boundary. 3- Select snapping, load error and load unlinks with RCL (decimal 9). 4- Open the Open Graphs tab and add the cleaned road layer to the layer section. 5- Select the segment (n radius) and press the Calculate button. 6- And the faulty, fragmented road network comes out :) — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#183>, or unsubscribe https://github.com/notifications/unsubscribe-auth/ADLJBFFUNO7PGHWWTXTN253SIBENJANCNFSM4R4HIB3Q . -- Ioanna Kolovou GIS analyst and developer

Hello, Ioanna, thank you very much. I was able to solve many of my problems with this new version. However, there are still some problems. There is no tutorial video or pdf for the new version. Let me tell you about the steps I have made with the new version and I would be very grateful if you help me with this. 1- I'm importing OSM data into QGIS. 2- I delete the paths that are cycleway, footway, steps from the attribute table. 3- Run RCL and then I'm running simplify geometries. 4- Then I process the simplify road layer with the network segmenter plugin. 5- I open the resulting layer with Graph Analysis and when the Segment or Road center line option is clicked, I select the segment option and press the calculate button. (Weighted off)

However, this often waits for a long time at 0 percent. Can you help me with this? Can you make a short tutorial video for me?

@haktank5 In principle you are doing everything correctly. Segment angular analysis with a radius N can take a very long time with a large map.

To make sure everything is working for you, I suggest you run the analysis with a very short radius, like 100m (step 5), or alternatively create a small map of your city after step 4, and analyse only this small map.

If the processing completes and the results look as expected, then you can run the large map, but have to wait...

@ haktank5 Prensip olarak her şeyi doğru yapıyorsunuz. N yarıçaplı segment açısal analizi, büyük bir haritayla çok uzun sürebilir.

Her şeyin sizin için çalıştığından emin olmak için, analizi 100 m gibi çok kısa bir yarıçapla çalıştırmanızı (5. adım) veya alternatif olarak 4. adımdan sonra şehrinizin küçük bir haritasını oluşturmanızı ve yalnızca bu küçük haritayı analiz etmenizi öneririm.

İşlem tamamlanırsa ve sonuçlar beklendiği gibi görünüyorsa, büyük haritayı çalıştırabilirsiniz, ancak beklemeniz gerekir ...

Thanks Jorgegil. I did as you said and achieved a successful result. But when I analyze for 500 meters and 5000 meters, for example, what could be the reason why I got the same result in both? You said in another post that you are related to CRS. But where I live, which is set according to the CRS Turkey. However, the plugin does not work on WGS84 4326. I choose the CRS as 3857. However, although the analysis is successful this time, the results are the same.

One more question: Can I make an axial analysis of the Open street map road network as R = n? Is OSM data only suitable for segment analysis? What does it mean when I choose segment or road center line in Graph Analysis?

@haktank5 You should not get the same results in 500 and 5000 metres, unless there's problem with the units. The analysis can only run on projected coordinate systems with metric units. The 3857 is a projected world coordinate system for mapping apps, you should choose the local coordinate city of the system you are analysing.

Also, it is not clear what you mean by same result, in which analysis measure?

Axial analysis is for axial maps, as the name indicates, so it cannot be used in segment or road centre line maps as the results will be meaningless.

SpaceGroupUCL / qgisSpaceSyntaxToolkit

OSM Road Data Fails! #183