topic Re: Conditional Statement in ArcGIS Spatial Analyst Questions

Conditional Statement

johnmonks — Tue, 04 Jul 2017 15:30:59 GMT

Hey, so, having frustraited over this for ages I give up and will ask

I have a conditional statement I applied to an NDVI layer to apply a double sided membership function to it

It is in 32 bit float as it is decimal. The following statement was used

Con((Float("spainndvi" < 0.13)) & (Float("spainndvi" > 0.9)), 0, Con((Float("spainndvi" >= 0.13)) & (Float("spainndvi" <= 0.32)), (Float("spainndvi" - 0.13)) / (0.32 - 0.13)), Con((Float("spainndvi" >= 0.6)) & (Float("spainndvi" <= 0.9)), (Float(0.9 - "spainndvi")) / (0.9 - 0.6), 1))

The odd thing is it worked when I last used it but having miss named the file I deleted it by accident, went to re-run the statement and it just gives me an error. Is there something obviously wrong with my statement? Thanks

Re: Conditional Statement

johnmonks — Tue, 04 Jul 2017 15:32:16 GMT

Messages
Executing: RasterCalculator Con((Float("spainndvi" < 0.13)) & (Float("spainndvi" > 0.9)), 0, Con((Float("spainndvi" >= 0.13)) & (Float("spainndvi" <= 0.32)), (Float("spainndvi" - 0.13)) / (0.32 - 0.13)), Con((Float("spainndvi" >= 0.6)) & (Float("spainndvi" <= 0.9)), (Float(0.9 - "spainndvi")) / (0.9 - 0.6), 1)) "E:\Users\GTAV\My Documents\ArcGIS\Default.gdb\rastercalc"
Start Time: Tue Jul 04 17:25:11 2017
Con((Float(Raster(r"spainndvi") < 0.13)) & (Float(Raster(r"spainndvi") > 0.9)), 0, Con((Float(Raster(r"spainndvi") >= 0.13)) & (Float(Raster(r"spainndvi") <= 0.32)), (Float(Raster(r"spainndvi") - 0.13)) / (0.32 - 0.13)), Con((Float(Raster(r"spainndvi") >= 0.6)) & (Float(Raster(r"spainndvi") <= 0.9)), (Float(0.9 - Raster(r"spainndvi"))) / (0.9 - 0.6), 1))
ERROR 000539: Error running expression: rcexec()
Traceback (most recent call last):
File "<expression>", line 1, in <module>
File "<string>", line 5, in rcexec
File "e:\program files (x86)\arcgis\desktop10.5\arcpy\arcpy\sa\Functions.py", line 263, in Con
where_clause)
File "e:\program files (x86)\arcgis\desktop10.5\arcpy\arcpy\sa\Utils.py", line 53, in swapper
result = wrapper(*args, **kwargs)
File "e:\program files (x86)\arcgis\desktop10.5\arcpy\arcpy\sa\Functions.py", line 257, in Wrapper
where_clause)
File "e:\program files (x86)\arcgis\desktop10.5\arcpy\arcpy\geoprocessing\_base.py", line 510, in <lambda>
return lambda *args: val(*gp_fixargs(args, True))
ExecuteError: ERROR 999999: Error executing function.
An invalid SQL statement was used.
An invalid SQL statement was used. [VAT_boole_ras]
An invalid SQL statement was used. [SELECT * FROM VAT_boole_ras WHERE E:\Users\GTAV\My Documents\ArcGIS\Default.gdb\ifthe_ras1]
Failed to execute (Con).

The table was not found. [VAT_ifthe_ras1]
Failed to execute (RasterCalculator).
Failed at Tue Jul 04 17:25:24 2017 (Elapsed Time: 12.36 seconds)

Re: Conditional Statement

DanPatterson_Retired — Sat, 11 Dec 2021 19:38:19 GMT

just working on syntax... it looks like you were whipping in brackets until problems went away

Con((Float("spainndvi" < 0.13)) & (Float("spainndvi" > 0.9)), 0,
 Con((Float("spainndvi" >= 0.13)) & (Float("spainndvi" <= 0.32)), 
     (Float("spainndvi" - 0.13)) / (0.32 - 0.13), 
     Con((Float("spainndvi" >= 0.6)) & (Float("spainndvi" <= 0.9)), 
         (Float(0.9 - "spainndvi")) / (0.9 - 0.6), 1)))a = Float("spainndvi"
# would be better
# generically
Con((a < 0.13) & (a > 0.9), 0,
    Con((a >= 0.13) & (a <= 0.32), (a - 0.13) / (0.32 - 0.13),
        Con((a >= 0.6) & (a <= 0.9), (0.9 - "spainndvi") / (0.9 - 0.6), 1)))
# I think.....‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

John... you posted this as a 'discussion' not a 'question'. If you need an answer, the 'questions' are better since they garner more attention than discussions. Generally 'discussions' are only addressed when people have time or they are interested.

Re: Conditional Statement

johnmonks — Tue, 04 Jul 2017 17:40:26 GMT

Hmm I had that before but it was having issues because it was decimal which is the reason I added float, but that appears to have fixed it so thanks a lot Dan, very helpful as always

Re: Conditional Statement

DanPatterson_Retired — Tue, 04 Jul 2017 17:49:27 GMT

John.... a bracket was out of order... can't remember which one off hand... the float thing is just to make your life easier that trying to do things all at once. You can have multiple lines in the raster calculator, so there is no need to go through the pain of trying to get it all in one line with all things that need to be done.

Re: Conditional Statement

JayantaPoddar — Tue, 04 Jul 2017 20:10:24 GMT

Apart from the parenthesis, the operators also look incorrectly placed. e.g. a number cannot be less than 0.13 and greater than 0.9. Or maybe you wanted the value to be 0.09 instead of 0.9.

Check the following expression:

Con((Float("spainndvi") < 0.13) | (Float("spainndvi") > 0.9), 0, Con((Float("spainndvi") >= 0.13) & (Float("spainndvi") <= 0.32), (Float("spainndvi") - 0.13) / (0.19), Con((Float("spainndvi") >= 0.6) & (Float("spainndvi") <= 0.9), (0.9 - (Float("spainndvi"))) / (0.3), 1)))

EDITED: The above expression to include OR "|"

Re: Conditional Statement

DanPatterson_Retired — Sat, 11 Dec 2021 19:38:22 GMT

interesting... but it doesn't produce an error, just an unexpected response.

(a < 0.13) & (a > 0.9)
Out[2]: False‍‍

Re: Conditional Statement

JayantaPoddar — Tue, 04 Jul 2017 20:45:28 GMT

Error might be due to incorrect use of parenthesis.

Re: Conditional Statement

DanPatterson_Retired — Tue, 04 Jul 2017 20:53:54 GMT

it was... can't remember which one was misplaced and if I can remember, that made one missing. The prior step to simplify things would have removed a whole load of parenthesis... I think the help files should show some multiline examples instead of the simple ones they do... perhaps when we have time

Re: Conditional Statement

johnmonks — Wed, 05 Jul 2017 00:41:35 GMT

Hey forgive my lack of insight but say for NDVI I thought the statement Con((Float("spainndvi") < 0.13) & (Float("spainndvi") > 0.9), 0 would specify that any number that is lower than 0.13 and higher than 0.9 will be attributed a value of 0?

Re: Conditional Statement

DanPatterson_Retired — Sat, 11 Dec 2021 19:38:25 GMT

that would be 'or' ... a number can't be both... as in 'and', I can't remember off hand, but I think it is vertical bar '|' for or (I would have to check it up for the spatial analyst

a = 0.5    # start with a value of 0.5

(a < 0.3) & (a > 0.9)
Out[2]: False

(a < 0.3) | (a > 0.9)
Out[3]: False

a = 0.1    # try a new one with the same conditions

(a < 0.3) & (a > 0.9)
Out[5]: False

(a < 0.3) | (a > 0.9)
Out[6]: True

a = 1.     # let's go to the other possible side

(a < 0.3) & (a > 0.9)
Out[8]: False

(a < 0.3) | (a > 0.9)
Out[9]: True
‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Re: Conditional Statement

JayantaPoddar — Wed, 05 Jul 2017 04:14:48 GMT

Hi John,

Could you try out the expression that I have mentioned in my above comment?

Re: Conditional Statement

JayantaPoddar — Wed, 05 Jul 2017 04:58:33 GMT

I think It should be (Float("spainndvi") <= 0.32) instead of (Float("spainndvi" <= 0.32))

Re: Conditional Statement

DanPatterson_Retired — Sat, 11 Dec 2021 19:38:27 GMT

I worked with the generic form, it was getting too hard to follow, then I tried to back fill

Con((a < 0.13) & (a > 0.9), 0, then the rest.....
but it should have been
Con((a < 0.13) | (a > 0.9), 0, then the rest.....‍‍‍

Re: Conditional Statement

johnmonks — Wed, 05 Jul 2017 10:48:20 GMT

Dan - I tried them both and it was indeed only taking one of the elements which was > 0.9 and therefor low values were given a wrong suitability, so much appreciated

Jayanta - I went back and tried the expression and it worked just fine and gave me the result I wanted as well so it seems that both ways work fine but I'm surprised it worked without the float because originally it was producing an integer result

Either way it produced the NDVI layer that I wanted so big thank you to you both

Re: Conditional Statement

johnmonks — Wed, 05 Jul 2017 11:10:45 GMT

Interestingly though, in regards to the brackets

Con(Float("tmp" > 8.64), 0, Con((Float("tmp" <= 8.64)) & (Float("tmp" >= 4.31)), (Float(8.64 - "tmp")) / (8.64 - 4.31), 1))

produced the same result as

Con(("tmp" > 8.64), 0, Con(("tmp" <= 8.64) & ("tmp" >= 4.31), (8.64 - "tmp") / (4.33), 1))

even though the brackets in the first one seem wrong.

Re: Conditional Statement

curtvprice — Sat, 11 Dec 2021 19:38:30 GMT

Hey John,

This statement doesn't have much effect:

Float("tmp" > 8.64)‍‍‍‍

because you are floating a boolean result, so you get 1.0 if true 0.0 if false. It is more efficient just leave it as boolean.

You only get integer out of a divide ("/") operation if both the inputs are integer (or boolean).

If you want to force a float raster out raster calculator, put a single Float() around the whole expression.

One more thing, you can avoid some code because of the "else" behavior of Con. If tmp has a value and is <= 8.64, this can be assumed to make it to the else expression.

These expressions are equivalent:

Con(("tmp" > 8.64), 0, Con(("tmp" <= 8.64) & ("tmp" >= 4.31), (8.64 - "tmp") / (4.33), 1))
Con(("tmp" > 8.64), 0, Con(("tmp" >= 4.31), (8.64 - "tmp") / 4.33, 1))‍‍‍‍
# both the folowing approaches will force a float raster output:
Con(("tmp" > 8.64), 0.0, Con(("tmp" >= 4.31), (8.64 - "tmp") / 4.33, 1.0))‍‍‍‍
Float(Con(("tmp" > 8.64), 0, Con(("tmp" >= 4.31), (8.64 - "tmp") / 4.33, 1))‍‍‍‍)‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

* small update. To avoid the error message: "the truth value of a raster is ambiguous" you need parentheses around the comparison expressions.

https://community.esri.com/message/14091?sr=search&searchId=966e684e-305f-4ee4-9ca7-99a811458cfa&searchIndex=0‌