How much area is overlap

Question

I am able to check if two geometries are intersecting through:

 if a.geometry().intersects(b.geometry()):

Is there any method available that tell me if how much one geometry is overlapping with other. Like 10% 50% 90% etc

How about the difference method? – Ian Turton Sep 28 '16 at 12:59 — Ian Turton, Sep 28 '16 at 12:59
where it is? is this built in i didnt find in geometry – Muhammad Faizan Khan Sep 28 '16 at 13:01 — Muhammad Faizan Khan, Sep 28 '16 at 13:01

Ian Turton · Answer 1 · 2016-09-28T14:46:25.600

1

From inspection of this question it looks like you can do something like:

if a.geometry().intersects(f.geometry()):
        intersection = a.geometry().intersection(f.geometry())
        print intersection.area()

When you intersect two polygons this can return either a polygon, a line or a point (depending on how the two polygons intersect), if you intersect a polygon and a line it will return either the line that is within the polygon or a point if the line just touches the polygon. So you need to add some logic that decides whether to calculate the area of the overlap or the length of the line depending on what sort of geometry intersection has returned.

edited Sep 28 '16 at 14:46

answered Sep 28 '16 at 13:14

Ian Turton

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is there any way available to check that how much line contains inside polygon. actually I want to check that – Muhammad Faizan Khan Sep 28 '16 at 14:37
use length instead of area to find the length of the line – Ian Turton Sep 28 '16 at 14:38
i did but i have polygon which provide area while line provide length both are different things. how can i compare it – Muhammad Faizan Khan Sep 28 '16 at 14:39
http://gis.stackexchange.com/questions/212297/compare-how-much-line-contains-inside-polygon – Muhammad Faizan Khan Sep 28 '16 at 14:40

julsbreakdown · Accepted Answer · 2017-06-21T06:44:38.757

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Calculate area for all the features using a loop:

for f in layer.getFeatures()

Getting the area can be done with :

f.geometry().area()

F being the feature
Then simply do a.area()/b.area()*100

edited Jun 21 '17 at 06:44

answered Sep 28 '16 at 10:05

julsbreakdown

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Thanks juls, i am checking it. is there not any build in function available – Muhammad Faizan Khan Sep 28 '16 at 10:16
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This won't give the geographical overlap area just the percentage of one regions area compared to another. – T_Bacon Sep 28 '16 at 10:18
Thank for the logic. can u help me here http://gis.stackexchange.com/questions/212223/copy-column-into-another-layer-column-programatically – Muhammad Faizan Khan Sep 28 '16 at 10:43
it is perfectly valid but i got another problem i have one layer of polygon while other is line. now how can i compare? one consist of area while other consist of length – Muhammad Faizan Khan Sep 28 '16 at 11:41

score 0 · Answer 3 · answered Sep 28 '16 at 13:35

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Divide the overlapped area by the whole area to get the percentage of overlapping:

intersection = a.geometry().intersection(b.geometry())  
totalArea = a.geometry().area() + b.geometry().area()  
percetnage = (intersection/totalArea)*100

answered Sep 28 '16 at 13:35

Shiko

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is there any way available to check that how much line contains inside polygon. actually I want to check that – Muhammad Faizan Khan Sep 28 '16 at 13:55
what do you mean by line ? is it another layer ? – Shiko Sep 28 '16 at 13:57
A polygon layer geomoery contains a line which is another layer. i want to check that how much that line contains in polygon. – Muhammad Faizan Khan Sep 28 '16 at 14:03
You can use Spatial query in QGIS to query lines intersecting with polygon and you will get all lines – Shiko Sep 28 '16 at 14:07
actually i have to update attribute table column value on this comparison basis – Muhammad Faizan Khan Sep 28 '16 at 14:18
You can create spatial join between the 2 layers and then update the column. for more details check http://www.qgistutorials.com/en/docs/performing_spatial_joins.html – Shiko Sep 28 '16 at 14:22

How much area is overlap

3 Answers3