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Urban Change Detection

by Technical Evangelist on ‎09-29-2015 01:30 PM - edited on ‎04-21-2016 06:09 AM by Technical Evangelist (3,524 Views)

Download model and sample data

Description:

This model finds differences in two different dates of ‘info-stack’ raster files, and produces a raster file showing positive or negative changes. These changes usually correspond to buildings or other infrastructure being added or removed. In addition, areas of removed trees are mapped.


‘Info-stack’ is a term used to describe a raster data set made up of layers which are not necessarily all "imagery", and in this context refers to a raster file with blue, green, red and NIR optical bands that have been radiometrically corrected, and a fifth band that specifies elevation for each pixel. The elevation band was generated automatically from the stereo imagery using a technique called semi global matching. Creation of the info-stack must be performed previously and is not part of this model.

 

The model primarily uses the 5th band (elevation). The part of the model that maps removed trees also uses the optical bands.

 

Below: Images left to right – Info-stack for 2010, info-stack for 2012, and changes detected by the model overlaid on the 2012 info-stack. This example shows medium and large positive change (yellow and orange) representing where houses have been added, and removed trees (green). The info-stack files are displayed using a 4/3/2 to red/green/blue band combination.

urban_change_detection_v15-1-2_input_output_attribute_table.png

 

                                              Below: urban_change_detection_v15-1-2.gmdx

urban_change_detection_v15-1-2.png

 

 

                                                   Below: Neighborhood Area submodel

urban_change_detection_v15-1-2_submodel_1.png

 

                                                   Below: Assign Attributes submodel

       urban_change_detection_v15-1-2_submodel.png

 

Input parameters:

Earlier info stack: (filename with path) of the earlier date input raster info-stack file. Info-stack is described at the beginning of this document.

Later info stack: (filename with path) of the later date input raster info-stack file. Info-stack is described at the beginning of this document.

Output results file: (filename with path) of the output raster file. This file is a single band thematic raster file with various colors noting the type of change. The meaning of the colors is described earlier in this document.

Minimum elevation change for building detection (feet): (float)(default 8.0) Minimum elevation difference between dates for non-vegetation change. Only negative change (trees removed) is considered by the model.

Minimum area size for buildings (pixels, sq meters): (integer)(default 100) Non-vegetation change areas must be at least this size. The sample data (info-stacks) pixels equal 1 square meter, so, in this case pixels are equivalent to square meters.

Minimum elevation change for trees (feet): (float)(default 5.0) Minimum elevation difference between dates for vegetation change.

Minimum area size for trees (feet): (integer)(default 50) Vegetation change areas must be at least this size. The sample data (info-stacks) pixels equal 1 square meter, so, in this case, pixels are equivalent to square meters.

Noise filtering amount (0-none, 1-low, 2-med, 3-high): (integer)(default 2) In effort to reduce noise, various levels of noise filtering are available to the model.

urban_change_detection_v15-1-2_run_dialog.png

 

Example data:

The following example info-stack data is for El Paso, Texas. Info-stack is described at the beginning of this document. The sample data supplied with this model is courtesy of HxIP - Hexagon Imagery Program (http://www.leica-geosystems.us/en/HxIP-Hexagon-Imagery-Program_106454.htm). 

The original images of El Paso, Texas were acquired on August 26, 2010 and August 30, 2012. Leica XPro software used stereo pairs of each date to generate a DSM (digital surface model). The software created a 5-band file where the first 4 bands are imagery (orthorectified using the DSM), and the 5th band is the DSM (elevation units of decimeters).

This 5-band data set was then preprocessed in ERDAS IMAGINE, converting the image pixel values to ground reflectance. A small subset of this resulting 5-band file is provided as example data. The band order is blue, green, red, NIR, and the DSM.

2010a_info_stack_subset.img – West El-Paso info-stack for the year 2010.

2012a_info_stack_subset.img – West El-Paso info-stack for the year 2012.

Comments
by Dwima
on ‎02-27-2018 07:59 PM

Hello.. can we use the other data for DSM, without we generated from the Multispektral data? 

by sbent
on ‎02-28-2018 06:02 AM

@Dwima

Yes, you can use other elevation data for the fifth band of your info-stack raster files. The DSM does not have to be generated from your multispectral data.

 

by Dwima
‎02-28-2018 06:48 AM - edited ‎02-28-2018 06:50 AM

Minimum elevation change for building detection (feet): (float)(default 8.0) --> does it mean if elevation of a building under 8 feets , although it was there, in later info stack (it wasn't there before or it be a change from earlier info stack) it may can't be detected by algorithm, or it can't be detected as a change?

by sbent
on ‎02-28-2018 08:14 AM

If the height of a new building in the later info-stack is under 8 feet it will not be included in the output change detection results when using the default value of 8 feet for the Minimum elevation change for building detection parameter. You can change this value when you run the model if you want to detect shorter buildings (decrease the value) or if you want to exclude taller buildings (increase the value) from the results. Keep in mind that if you decrease the value below 8 feet for the Minimum elevation change for building detection parameter the output change detection results may include features that are not buildings.

by Dwima
on ‎03-01-2018 02:03 AM

ohh okay, thankyou.. so helpfull ^_^

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