Why does Raster Calculator return GRID ERROR-Unable to open input grid?

Question

I'm calculating Simple Ratio (SR) from NDVI using Raster calculator in Arcgis. Here is expression I wrote in Raster calculator.

SR=(1+float[NDVI_apr.tif])/(1-float[NDVI_apr.tif])

But when I evaluate this expression, the following error always appear on the screen.

GRID ERROR-Unable to open the input grid: 1+FLOATC:\document\... Error in executing grid expression.

What is wrong with this expression?

are you giving spaces between all operators? ( 1 + float[NDVI_apr.tif] ) / ( 1 - float[NDVI_apr.tif] ) — Gago-Silva
– Gago-Silva, Commented Dec 2, 2012 at 9:57
Yes, I did. But result is the same, showing me the above error. The NDVI_apr.tif image is raster image. I want to ask 2 things. 1. Can the raster image be used directly in raster calculator in Arcgis. I read it can, but I'm not sure. Or Is it necessary to convert it into grid. 2. The NDVI image is in D disk on my computer (not in GIS working directory). Is it ok? — user3063
– user3063, Commented Dec 2, 2012 at 11:58
Doesn't Float need a capital F in Raster Calculator as per example here? — PolyGeo
– PolyGeo ♦, Commented Dec 3, 2012 at 1:56
I'm not sure how you can calculate the SR from an NDVI. Isn't the simple ratio nIR/red? — Aaron
– Aaron ♦, Commented Dec 4, 2012 at 4:35

PolyGeo · Accepted Answer · 2015-06-28 23:01:56Z

write your expression using raster calculator buttons . don't write / + - * using pc or laptop keyboard.

your expression must be like this :

sr =(1 + Float("NDVI_apr.tif")) / (1 - Float("NDVI_apr.tif"))

this expression work properly in ArcGIS 10

PolyGeo · Accepted Answer · 2012-12-03 01:57:48Z

Float appears to need a capital F in Raster Calculator as per example here which is probably why @wetland Answer has expression working.

2 Answers 2