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New Contributor
Posts: 4
Registered: ‎06-20-2019

Accuracy Assessment Issue

[ Edited ]

hello , I am new to this website , so I am sorry if this is not where I am supposed to post my problem. 

I am trying to apply an accuracy assesment for a classification image that i recoded to 4 classes using te recode tool in erdas imagine, I chose 1024 number of search count ,  110 for the number of point and equalized random , then apply . I got the message saying this:  'reached the maximum number of search point 1024! so far collected 16 random coordinate. Would you like to continue with an other set of 1024 search points?' 

then i press yes but this message keep comming up i, i press yes again but same thing happend again anad again,  and the accuracy assesment doesn't finish . 

Do you have any solution?

 

ps: I use Erdas imagine 2014

Technical Evangelist
Posts: 798
Registered: ‎10-01-2015

Re: Accuracy Assessment Issue

Sounds like the strategy you have chosen is not appropriate to the distribution of classes you have? Try a different strategy and/or increase the number of points to search (to give the algorithm a better chance of finding the number and distribution you have requested).

 

Cheers

 

Ian Anderson
Chief Product Owner, Desktop Remote Sensing
Hexagon Geospatial
New Contributor
Posts: 4
Registered: ‎06-20-2019

Re: Accuracy Assessment Issue

Thanks for your quick reply,

I changed the number of points and the number oh search points many times but still having the same results .

 

Technical Evangelist
Posts: 798
Registered: ‎10-01-2015

Re: Accuracy Assessment Issue

[ Edited ]

What are the counts (histogram) for each class (including any background classes) in your image? If one (or more) of your classes has a small histogram count then it may be impossible (or very unlikely) to randomly include the required equalised number of pixels of that class and you will need to use one of the other strategies instead.

 

Cheers

Ian Anderson
Chief Product Owner, Desktop Remote Sensing
Hexagon Geospatial
New Contributor
Posts: 4
Registered: ‎06-20-2019

Re: Accuracy Assessment Issue

Hello, 

 

I have 11 class: from class1 to class10 and an unclassifes class,here are the histograms values for each class:

Unclassified: 473013217

Class1:5448664

Class2:4909695

Class3:4929556

Class4:3431779

Class5:4236277

Class6:5051267

Class7:5647940

Class8: 6251155

Class9: 6391328

Class10: 966492

 

I recoded these classes using the recode tool to these new values:

 

Unclassified: 0

Class1:2

Class2:0

Class3:3

Class4:3

Class5:1

Class6:0

Class7:0

Class8: 0

Class9: 0

Class10: 0

 

After this, i applyed the accuracy assesment tool and then couldn't have the result because of the problem i mentionned in mu first message.

 

PS: I need only the classes recorded to: 1 , 2 and 3 . I didn't know how to delete the other class from the attribute table because the classification is a .img file .

 

 

Cheers

 

 

Technical Evangelist
Posts: 798
Registered: ‎10-01-2015

Re: Accuracy Assessment Issue

Hi salma,

 

The Unclassified class is huge compared to the others. Have you excluded it from the point creation process (by using the Select Classes button)? If not, the 1024 random points that get thrown down are almost always going to be in the Unclassified locations if you're using Equalized as the distribution strategy. Try excluding Unclassified, or try Stratified instead.

 

Cheers

 

Ian Anderson
Chief Product Owner, Desktop Remote Sensing
Hexagon Geospatial
New Contributor
Posts: 4
Registered: ‎06-20-2019

Re: Accuracy Assessment Issue

Hello , 

 I selected only the classes that I want (using the Select Classes button as you mentionned), but still having that problem.  Same thing even when I use the Stratified method.

 

Cheers

Technical Evangelist
Posts: 798
Registered: ‎10-01-2015

Re: Accuracy Assessment Issue

Hi salma,

 

That may be an issue with ERDAS IMAGINE 2014 then. You may wish to ocntact your local Support group for further assistance.

 

Cheers

 

Ian Anderson
Chief Product Owner, Desktop Remote Sensing
Hexagon Geospatial