ARCGRIDWRITE

Write gridded data set in Arc ASCII Grid Format

Description

ARCGRIDWRITE converts data in a matlab grid (as produced by eg. meshgrid and griddata) into a text file in Arc ASCII Grid Format. The file can also be automatically converted to raster on PC's with ARCINFO installed.
 
EXAMPLE - create a raster grid of the peaks function
[X,Y,Z]=peaks(100);
arcgridwrite('peaksArc.asc',X,Y,Z,'precision',3, 'convert')
 
NOTES
Because the Arc ASCII format has only one parameter for cell size, both X and Y must have the same, non-varying grid spacing.

• MATLAB release: MATLAB 7.8 (R2009a)

[Colin Lazauski]

This is a nice file and works well. Modification of the header section write format will allow the file to be read directly by ESRI Arc-GIS. My modification is:

%write header
fprintf(fid,'%s','ncols ');
fprintf(fid,' %d\n',nz);
fprintf(fid,'%s','nrows ');
fprintf(fid,' %d\n',mz);
fprintf(fid,'%s','xllcorner ');
fprintf(fid,[dc,'\n'],minX);
fprintf(fid,'%s','yllcorner ');
fprintf(fid,[dc,'\n'],minY);
fprintf(fid,'%s','cellsize ');
fprintf(fid,'%-6.0d\n',dx);
fprintf(fid,'%s','NODATA_value ');
fprintf(fid,'%-5.0d\n',-9999);

This place the numeric values starting in column 15 and removes the trailing zeros from the last two values.

[Andrew Stevens]

Colin,

Thanks for your comments. I found after playing with a couple examples, I determined that if I simply change the output filename from .txt to .asc that the file can be read directly into arc without doing the raster conversion.

I would also be careful with your modification of the way the header is written in the output file. Your modification forces the cell-size to be an integer which would produce a large error in many of my datasets.

Andrew

[Daniya]

 

[Edward Bair]

Thanks for the util. It may be the way I'm building the grid, but ARCGRIDWRITE creates rasters that are flipped vertically for me. If Z is my raster, I need to do the following to have it written correctly:

[iv,jv]=ndgrid(1:size(Z,1),1:size(Z,2));
arcgridwrite('VegGrid_small.asc',jv,iv,flipud(Z));

[Edgar]

Andrew,

Thanks for the script. However, I found the script is not able to write high resolution cellsizes. My grid has a resolution of 0.075. However, the scripts writes: "0.000". How can I solve this?? Thanks.

EM

[Andrew Stevens]

Edgar,

The default precision for the function is %0.3f, so you should get 0.075 as the cell spacing. I tried the following code to verify:

%generate synthetic data with desired %cell spacing
xi=0:0.075:1;
yi=0:0.075:1;
[xm,ym]=meshgrid(xi,yi);
zm=peaks(numel(xi));

%call arcgridwrite
arcgridwrite('test.asc',xm,ym,zm);

%look at output
type('test.asc')

The results look correct to me. Let me know (by email) if you have further questions.

[A Westergaard]

Andrew,
Thank you for sharing your work. As I am new to MatLab, I hope you or others have time for some guidance: In Matlab I have a matrix with values [-1:1]. I want to export this matrix to ArcMap. What would the syntax be for this? Thank you in advance.

[A Westergaard]

The above mentioned matrix has 350 rows and 300 columns. Values are double.