gpt MosaicGeneral

avmehta · by **avmehta** » Wed Feb 17, 2021 12:45 am America/New_York

Hello,
Could you please explain the following segment in the xml file from https://seadas.gsfc.nasa.gov/help/GptCookbook/gptCookbookMosaic.html
   <conditions>
<condition>
<name>condition_0</name>
<expression>${qualityExpression}</expression>
<output>false</output>
</condition>
</conditions>
<combine>OR</combine>

Not sure what condition_0 is and also   <combine>OR</combine>.
   Corresponding parameter file is also available after the xml file at the above link.
Thanks.
Amita

gnwiii · by **gnwiii** » Wed Feb 17, 2021 9:27 am America/New_York

condition_0 is an arbitrary name for the qualityExpression, but it is helpful to use a descriptive name such as "valid_range" The Help documentation has many pages of information on Mosaic (under Raster/Geometry/Mosaic and the GPT Cookbook) that explains how a qualityExpression is used. The Raster/Geometry/Mosaic help includes a section for Conditions. To make sure you understand what the conditions do you should experiment in the GUI with your data (one product) and different conditions.

avmehta · by **avmehta** » Wed Feb 17, 2021 9:39 am America/New_York

Thank you so much.
Amita

gnwiii · by **gnwiii** » Wed Feb 17, 2021 9:48 am America/New_York

condition_0 is an arbitrary name for the "qualityExpression". It is helpful to use a descriptive name such as "flags_masked" or "valid_range" The Help documentation has many pages of information on Mosaic (under Raster/Geometry/Mosaic and the GPT Cookbook) that explains how a "qualityExpression" is used. The Raster/Geometry/Mosaic help includes a help section for the "Variables & Conditions" tab. To make sure you understand what the conditions do you should experiment with your data in the GUI and different conditions. The GUI allows you to use the Expression editor, which can help avoid erros in entering expressions. Setting "Output" to "true" ("Outp." seems to be an abbreviation for "Output" -- maybe the tab wasn't wide enough for the full name) helps you determine how often a condition was triggered.

If something in Help documents is unclear please suggest how it can be improved.

by **OB SeaDAS - knowles** » Thu Feb 18, 2021 11:43 am America/New_York

Hi Amita,

As previously noted in this thread, rhos_412 and other surface reflectances can in fact be negative, and for that matter could be greater than 1.0 as well. Cloud shadow and cloud tops are 2 possible instances in which this might occur. There could be other instances. The fill value (-32767.0) is another instance.

The likelihood that the float value rhos_412 precisely equals zero is extremely small. Most likely you want something like (rhos_412 > 0.0 && rhos_412 <= 1.0) instead of (rhos_412 != 0) in your expression. If you wish to retain the "official" range then you want (rhos_412 >= -0.05 && rhos_412 <= 1.0).

avmehta · by **avmehta** » Thu Feb 18, 2021 12:40 pm America/New_York

Thanks so much Danny - will try this.
Amita

avmehta · by **avmehta** » Mon Feb 22, 2021 10:15 am America/New_York

Hi,
The xml file does not like && ! Any way I am going to use IDL to do mosaics as I want minimum, mean, and median values for the mosaics.
Thanks for your help.
Amita

gnwiii · by **gnwiii** » Mon Feb 22, 2021 4:22 pm America/New_York

You should be able to enter each inequality as a separate expression and set the "combine" method to "AND" in the xml file.