[GRASS-user] r.cost: exact meaning of percent_memory ?

[Markus Metz]

On Fri, Jan 23, 2015 at 6:16 PM, Moritz Lennert
<mlennert at club.worldonline.be> wrote:
> On 22/01/15 21:12, Markus Metz wrote:
>>
>> On Thu, Jan 22, 2015 at 2:30 PM, Moritz Lennert
>> <mlennert at club.worldonline.be> wrote:
>>>
>>> IIUC, this would mean that if I have a region of X DCELL cells, I would
>>> need: X*8 bytes of memory, or ?
>>
>>
>> No, it would need X * 3 * 8 bytes (if direction output is requested,
>> another X * 4 bytes). Considering that you are a power user and
>> developer, and that you do not understand the 'percent_memory' option,
>> it is high time to change that option to the standard memory option
>> where the user specifies the amount of memory in MB that should be
>> used.
>
>
> Yes. I do plead guilty for not haven taken the time to look at the code in
> detail to understand, but the man page definitely does not help. If this can
> be changed into the standard memory option, this would be great.

Done in trunk r64287 and relbr70 r64288.

The percent_memory option has been changed to memory (in MB) for both
r.cost and r.walk, these modules are siblings.

Markus M

> If this
> cannot be done soon, then a change to the man page would already be a plus,
> maybe indicating the calculations.
>
>>>
>>> So if memory available is > X*8 I should be able to use
>>> percent_memory=100
>>> (or at least 75). Is that correct ?
>>
>>
>> No, see also above, the input cost surface, the output accumulated
>> cost surface, and the cell value of the nearest starting point are
>> held in memory. If a direction output map is requested, this one is
>> also held in memory.
>
>
> This info should go into the man page.
>
> Moritz