[gdal-dev] Confusion reading .img raster band.

[Robert Denham]

Dear gdal-dev,
I am a bit confused reading data from an ERDAS Imagine
File. Using the tutorial as a guide I wrote a test program which just
prints out the values of the image in col/row order, just like the imagine
pixel->ascii function. Unfortunately it doesn't quite match up with the
imagine equivalent, but seems to duplicate the final pixel in each line.

let me show you:
The tree columns on the left are my results, the three on the right are
imagine results.
first line is fine, but the first value on the second line is the same as
the last value on he line above, which puts everything out.



X Y val	X Y B1
0 0 75.705154	0 0 75.7051544189453
1 0 75.349915	1 0 75.3499145507812
2 0 74.681129	2 0 74.6811294555664
3 0 74.023941	3 0 74.0239410400391
4 0 73.616539	4 0 73.6165390014648
5 0 73.284485	5 0 73.2844848632812
6 0 73.174126	6 0 73.1741256713867
7 0 73.244751	7 0 73.2447509765625
8 0 73.160934	8 0 73.1609344482422
9 0 73.078377	9 0 73.0783767700195
10 0 72.998413	10 0 72.9984130859375
11 0 72.918442	11 0 72.9184417724609
12 0 72.667473	12 0 72.6674728393555
0 1 72.667473	0 1 75.8207702636719
1 1 75.820770	1 1 75.3696441650391
2 1 75.369644	2 1 74.8217010498047
3 1 74.821701	3 1 74.3044281005859
4 1 74.304428	4 1 73.9780883789062
5 1 73.978088	5 1 73.332878112793
6 1 73.332878	6 1 73.317741394043
7 1 73.317741	7 1 73.2660064697266
8 1 73.266006	8 1 73.2488327026367
9 1 73.248833	9 1 73.1332397460938
10 1 73.133240	10 1 73.0532760620117
11 1 73.053276	11 1 72.9733047485352
12 1 72.973305	12 1 72.7634429931641
0 2 72.973305	0 2 75.8491439819336
1 2 72.763443	1 2 75.3893661499023

etc.

Here is the relevant bit of code I used:
hBand = GDALGetRasterBand (hDataset, 1);
nXSize = GDALGetRasterBandXSize (hBand);
nYSize = GDALGetRasterBandYSize (hBand);
pafScanline = (float *) CPLMalloc (sizeof (float) * nXSize * nYSize);
GDALRasterIO (hBand, GF_Read, 0, 0, nXSize, nYSize,
pafScanline, nXSize, nYSize, GDT_Float32, 0, 0);

for(row=0;row<nYSize;row++) {
for(col=0;col<nXSize;col++) {
printf("%d %d %f\n",col,row, pafScanline[row*nYSize+col]);
}
}

This might be a simple programming error but I'm not too proud to have the
obvious pointed out to me.

Thanks fro any suggestions,
robert 


------------------------------------
| Robert Denham |
| School of Mathematical Sciences |
| Queensland University of Technology |
| denham at f... |
------------------------------------