TransDEM Forum

I am trying to open geo-referenced raster maps downloaded from the Geogratis.Ca site. Some will load as is shown in Tutorial 8 while others do not. I can open 021A09 and process it. 021A08 works too. But 011D12 shows only a black rectangle with a coordinate grid. 021A08 and 021A09 are about 88 megapixels, while 011D12 is 97.7 megapixels. Is 011D12 a bit too big while the others just fit? If so, would doing all I can to increase available RAM maybe fix it?

Thank you.
Al the (civil) Engineer

My computer:
General
Operating System Microsoft Windows XP Professional
Central Processor AMD Athlon(tm) 64 X2 Dual Core Processor 5000+
Graphics
Video Adapter NVIDIA GeForce GTX 460
Video Memory 768.00 MB
Screen Resolution 1600 x 900
Storage
Total Memory 3.00 GB
Free Memory 1.85 GB
Total Hard disk 847.69 GB
Free Hard disk 391.40 GB
Memory Resource
Total Memory 3.00 GB
Used Memory 1.14 GB
Free Memory 1.86 GB
Memory Usage 38%
Video Adapter
Name NVIDIA GeForce GTX 460
Video Processor GeForce GTX 460
Manufactory NVIDIA
Video Architecture VGA
DAC Type Integrated RAMDAC
Memory Size 768.00 MB
Memory Type Unknown
Video Mode 1600 x 900 x 4294967296 colors
Current Refresh Rate 60 Hz
Driver Version 6.14.12.8026
Driver Date 03/08/2011 11:49:00 AM

Indeed, the image seems to be too big for at least one of the algorithms of the processing pipeline in TransDEM. I will have a closer look but won't make any promises. Unfortunately, more memory will not solve the problem.

Update: I found the cause of the problem.

TransDEM uses the GDI+ library which has a number of nice features such as being able keep compressed images in memory in compressed form, until access to the pixels is really needed. Unfortunately, GeoTIFF images are often uncompressed, as in this example. This particular image eats up 400MB and apparently exceeds some threshold. The next GDI+ Draw-to-an-image method fails, running out of memory on a temporary buffer internally.

What I now do in case of error is to compress this large image in memory, using jpeg encoding. It takes a while, but overcomes the memory limitation obstacle. The only catch is that all transparency will be lost. However, all will still work, if the user stays with the suggested processing order for large images: 1. reduce size, 2. reduce margins and 3. apply transparency.

This bypass will be included in TransDEM 2.2.