Sample-based area estimation

[Dodou Trawally]

Dear SEPAL users,

I have classified an image for sampled-based area estimation. I need support with the following issues:

1. the classification results (AOI) is split into two sub images, which means I need to recombine them into a unit AOI in order to use the image in the SAE-Design window.
1. Questions:
1. How can this splitting be avoided in the first instance?
2. If the splitting cannot be avoided, is there a tool in SEPAL that can recombine the two images?
2. I attempted working with the bigger of the two images cited above in the SAE-Design window but realised the following issues with the 'Strata areas' window
1. only the 'OFT' option is available not 'R' as given in the documentation
1. Question: Why is the option for using 'R' not available?
2. when i run the 'Area calculation and legend generation' button, it gives the error: 'gdalinfo missing'
1. Question: What is the cause of this error and how can it be resolved if it is not due to using only a part of the AOI as explained above

It will be very helpful to have some quick responses.

Best regards,

Dodou

[Dodou Trawally]

Dear SEPAL Users,

The error message in my earlier message should have read: 'could not find function "gdalinfo" and not 'gdalinfo missing'.

Best regards,

Dodou

[Amit Ghosh]

Dear Dodou,

The classification recipe relies on the Google Earth Engine API. When exporting a large AOI, the results are divided into multiple small tiles. Additionally, the recipe produces a virtual raster that can be conveniently used in the SAE-Design App to analyse the two images you have.
Another option is to utilise gdal_translate for merging these images:
These steps are necessary to accomplish that:

• Open the terminal
• cd to the download folder where you have these images

cd download/<CLASSIF name>

• run the following gdal command

gdal_translate -of GTiff <CLASSIF name>_<gee tile id>.vrt <merged_output>.tif

OFT is available  on SEPAL due to its faster performance compared to the R-based alternative. The reason for the 'gdalinfo missing' error is because the R legacy spatial libraries, which the SAE is built on, were discontinued on Nov 23. The app needs to be updated.

Best,

Amit

--

Amit Ghosh,

Geospatial expert,

Land and Water Division, FAO

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[Dodou Trawally]

Dear Amit,

Thank you for the prompt response. I will follow the instructions and let you know if necessary.

Best regards,

Dodou