@sindizzy Please check out

public static bool IsFloatingPoint(Type typ) { return typ is float | typ is double | typ is decimal; }.

VS is throwing CS0184 The given expression is never of the provided ('type') type warnings for all three types. Changing Type typ to ValueType typ as shown in your referenced link removes those errors but causes an error with the parameter given to IsFloatingPoint which is a Type. I have no data to try and check whether this works although it's throwing warnings.

Furthermore you stated you added examples or tests. I can see those test.txts you added but no MergeGridTest.cs. What are those test.txts for?

@jany-tenaj let me review the IsFloatingPoint routine. I remember I had some issues with it but it did compile. Ill take a look again.

The test.txts files are nothing more than simple tests to see how the logic to determine the best output data type works. For example, if the inputs are DTED and ASCII and the requested output is GRB what would be the best data type for the merge. I just dont have access to all the raster formats and data types.

@jany-tenaj ok I have updated IsFloatingPoint so that it now has no warnings.
I added tests for IsFloatingPoint and GetClosestType and the results look very good.
Then I added SimpleMergeGridsTest for some sample grids. It was failing so I named my routine ExecuteNew and re-added the production logic for Execute.

Oddly enough the current production logic also bombs. Maybe I am missing something on this method.
The FileType and DataType do not seem to reflect what's in the input rasters.

fileNameA=C:\Users\DarkPax\Documents\GitHub\DotSpatial\Source\Tests\DotSpatial.Tools.Tests\bin\Data\Grids\TIFF\GTOPO30.tif
gridA: min=137 max=238 cols=39 rows=24
gridA: FileType=Ascii DataType=System.Int16

fileNameB=C:\Users\DarkPax\Documents\GitHub\DotSpatial\Source\Tests\DotSpatial.Tools.Tests\bin\Data\Grids\BIL\GTOPO30.bil
gridB: min=125 max=215 cols=39 rows=24
gridB: FileType=Ascii DataType=System.Int16

fileNameOut=C:\Users\DarkPax\Documents\GitHub\DotSpatial\Source\Tests\DotSpatial.Tools.Tests\bin\Data\Grids\merged.bgd

The size of the file was 558 which didn't match the expected 5586380
Exception thrown: 'System.NullReferenceException' in DotSpatial.Data.dll
An exception of type 'System.NullReferenceException' occurred in DotSpatial.Data.dll but was not handled in user code
Object reference not set to an instance of an object.

Yeah I think something is not right.

var rstTypeA = Raster.GetGridFileType(fileNameA);
Debug.Print("gridA: RasterFileType={0}", rstTypeA);

var p = new GdalRasterProvider();
var gridA = p.Open(fileNameA);
Debug.Print("gridA: FileType={0} DataType={1}", gridA.FileType, gridA.DataType);

This outputs

fileNameA=\Source\Tests\DotSpatial.Tools.Tests\bin\Data\Grids\TIFF\GTOPO30.tif
gridA: RasterFileType=GeoTiff
gridA: FileType=Ascii DataType=System.Int16

It appears that the FileType (and maybe some other properties) are not set with the GdalRasterProvider.Open method. Should I be using Raster.Open instead?

I've got no idea. Never used this tool before

@jany-tenaj ok let me dig a little deeper.