topic Re: Rounding and converting raster values in ArcGIS Pro Questions

Rounding and converting raster values

BeckB — Tue, 27 Jul 2021 14:15:01 GMT

Hello,

I'm using ArcGIS Pro 2.8.1. I have a raster layer whose values I would like to round and then convert into a corresponding value. For example, if the current value is 9.788, I would round that to 10 and convert that to 144. Is there a way to do this?

Re: Rounding and converting raster values

JayantaPoddar — Tue, 27 Jul 2021 15:10:47 GMT

A RoundUp() function of (Raster Value minus 0.5), inside a Con() function should work.

In the following example, The Raster Calculator is checking for the Round Value is equal to 10. If the argument is true it will return 144. Else it will return the original Raster Value.

Con((RoundUp("RASTER" - 0.5)==10),144,"RASTER")

If required, you could further add Con() condition in place of the False Value (Nested condition). The ultimate False Value, I am keeping as 0 in this example.

Con((RoundUp("RASTER" - 0.5)==10),144,(Con((RoundUp("RASTER" - 0.5)==11),169,0)))

Hope it helps.

Re: Rounding and converting raster values

BeckB — Tue, 27 Jul 2021 15:14:31 GMT

Hello,

Thank you so much for this! Could you please clarify why 0.5 is subtracted?

Re: Rounding and converting raster values

JayantaPoddar — Tue, 27 Jul 2021 15:30:44 GMT

Good Question.

I couldn't find a function to do a proper Round, i.e. RoundDown values from decimal values of .0 to .499... and RoundUp Values from .5 to .99...

So deducting a 0.5 will always given me a value, which if Rounded Up, gives you the desired value.

A few examples

9.569 : 9.569-0.5=9.069: RoundUp(9.069)=10

9.0: 9.0-0.5=8.5: RoundUp(8.5)=9

9.25: 9.25-0.5=8.75: RoundUp(8.75)=9

*Just realised

The only issue is with values ending with .5 decimals.

9.5: 9.5-0.5=9.0: RoundUp(9.0)=9 (But you want 10 in this case) 😔

Alternatively, you could add 0.5 and use RoundDown() function.

Re: Rounding and converting raster values

BeckB — Tue, 27 Jul 2021 15:34:35 GMT

That makes sense! What would your recommendation be in cases of 0.5 decimals?

Re: Rounding and converting raster values

JayantaPoddar — Tue, 27 Jul 2021 16:11:48 GMT

How about this? First run the following Expression in Raster Calculator.

Con(("RASTER" - (RoundDown("RASTER"))== 0.5),RoundUp("RASTER"),"RASTER")

Use its output Raster as the input Raster of the expression in my first post. Like this

Con((RoundUp("NEWRASTER" - 0.5)==10),144,0)

You may choose to create a model in Model Builder, if this is a repetitive process.

I don't want to complicate the expression. That's why providing the solution in two steps.

Re: Rounding and converting raster values

DanPatterson — Tue, 27 Jul 2021 16:48:48 GMT

Is this value the only one that you want to round?

What is the significance of rounding it to 10, then converting it to 144?

Are you trying to scale a raster's data to a new range?

Re: Rounding and converting raster values

BeckB — Tue, 27 Jul 2021 17:18:38 GMT

There are multiple values I would like to round. In a nutshell, I have satellite data recorded in 16-day intervals, which are numbered 1-23. I want to convert these numbers to the Julian day of year (i.e. the 2nd timestep, currently labelled 2, would be converted to day 16). I need to round the numbers so I can identify which day of year it is closest to (i.e. if the value was 2.34, I would assign it to the second timestep, day 16). Please let me know if you need further clarification!

Re: Rounding and converting raster values

JayantaPoddar — Tue, 27 Jul 2021 19:08:54 GMT

Had Dan not asked the (appropriate) question, and you answered, I could have never imagined your question was related to Dates.

Let me try putting it in a single expression

Expression:

16*((Con(("RASTER" - (RoundDown("RASTER"))== 0.5),RoundUp("RASTER"),RoundUp("RASTER" - 0.5)))-1)+1

Re: Rounding and converting raster values

BeckB — Tue, 27 Jul 2021 18:33:06 GMT

Thank you both so much for catching this! JayanthaPoddar, could I ask again for you to clarify the purpose of subtracting 1?

Re: Rounding and converting raster values

JayantaPoddar — Tue, 27 Jul 2021 18:43:02 GMT

This is what I calculated. Please correct me if I am wrong.

Result of Con Function (Raster Value)	Con Function -1	Calculation of No. of Days	Julian Day
1	0	16 x 0	0
2	1	16 x 1	16
3	2	16 x 2	32
4	3	16 x 3	48
5	4	16 x 4	64
6	5	16 x 5	80
7	6	16 x 6	96
8	7	16 x 7	112
9	8	16 x 8	128
10	9	16 x 9	144
11	10	16 x 10	160
12	11	16 x 11	176
13	12	16 x 12	192
14	13	16 x 13	208
15	14	16 x 14	224
16	15	16 x 15	240
17	16	16 x 16	256
18	17	16 x 17	272
19	18	16 x 18	288
20	19	16 x 19	304
21	20	16 x 20	320
22	21	16 x 21	336
23	22	16 x 22	352

Re: Rounding and converting raster values

BeckB — Tue, 27 Jul 2021 18:55:13 GMT

This makes sense! However, in my case, the Julian day begins at 1, not 0. Here's a chart of the conversion; would this mean the subtraction is not necessary?

Re: Rounding and converting raster values

JayantaPoddar — Tue, 27 Jul 2021 19:09:32 GMT

Just add 1 at the end of the expression (outside all brackets). Updated my last expression.

Re: Rounding and converting raster values

BeckB — Tue, 27 Jul 2021 19:11:03 GMT

To clarify, do you mean like this?

16*((Con(("RASTER" - (RoundDown("RASTER"))== 0.5),RoundUp("RASTER"),RoundUp("RASTER" - 0.5)))-1)+1

Re: Rounding and converting raster values

JayantaPoddar — Tue, 27 Jul 2021 19:13:38 GMT

Yes.

Re: Rounding and converting raster values

BeckB — Tue, 27 Jul 2021 19:16:34 GMT

Okay, thank you so much!! I really appreciate your help.

Re: Rounding and converting raster values

Luke_Pinner — Wed, 28 Jul 2021 09:19:51 GMT

If your values are all positive, just add 0.5 before truncating.

Int("RASTER" + 0.5)

You can then reclassify the rounded values to whatever you want.