Matt Spencer New Member
Posts:14  
11 Aug 2017 05:27 AM |
|
Hi, I have a classified image (Maximum Likelihood) that I want to run an accuracy assessment on, however I am unsure of the correct steps in ENVI. I have done it before in Erdas Imagine where a set of random points is generated and then you determine the "true" class of each point, which then results in an overall accuracy % for the classification. I am using 10m Sentinel imagery to identify the "true" classes. I have tried the "Generate Random Sample Using Ground Truth Image" tool using my classified MLC image as input, used Stratified Random and input the amount of pixels I require for each category. So I now have ROIs for each classification category, but I am unsure of the next step to do something similar as in Erdas Imagine. Thanks.
|
|
|
|
Matt Spencer New Member
Posts:14  
13 Aug 2017 01:20 PM |
|
Sorry, I've realised that generating random points for each category is pointless because it will always result in 100% classification accuracy. Is there a way to generate random points on the image and then determine if they are the "true" class or not? Thanks.
|
|
|
|
MariM Veteran Member
Posts:2396  
15 Aug 2017 08:38 AM |
|
The idea is to use a ground truth image, which would be an already classified image of a known accuracy, to generate the random sample of points for accuracy assessment. So you would not want to use your MLC image you just created but another image of 'known accuracy' to compare. From this other image, you can either use Accuracy assessment using a Ground Truth image or ground truth ROIs, or ROIs generated on the classified image of known accuracy.
|
|
|
|
Matt Spencer New Member
Posts:14  
15 Aug 2017 01:38 PM |
|
Thanks, yes I understand now. I have a Sentinel-2A (10m) unclassified image resolution which I'm using as ground truth, although I know this isnt ideal I don't have access to the location I have classfied. So there is no way to use the Sentinel-2A image unless it is classified? Thanks.
|
|
|
|
MariM Veteran Member
Posts:2396  
16 Aug 2017 08:38 AM |
|
Yes, the post-classification tools expect either ground truth classification images for comparison or ROIs extracted from a ground truth classification image.
|
|
|
|
MARK Estelle New Member
Posts:1  
22 Aug 2017 02:44 AM |
|
This nice and useful info for me. Thanks a lot
|
|
|
|