All that is necessary is perceiving the target. IF you can perceive it with a D:Conc Intellego spell (perhaps maintained with Maintain the Demanding Spell) the Rego spell can be used effectively.
Yes, I was thinking of separate spells. First the InAn and then the actual summoning.
As I noted above, that'll still mean animals upwind and so forth remain undetected and unaffected by the summoning but I'm not sure if that's a tolerable limitation or not. Depends on what the player wants, I suppose.
You still have to be able to pin-point the target.
Hermetic Magic cannot target ie. a target you can only hear (compare: HMRE, Gruagach, p. 59-60 and the hermetic integration of improved voice range p. 78).
You have that turned around. The Gruagach can affect things he cannot perceive; a target who hears the Gruagach's voice that he doesn't know is there is affected by his spells. Page 78 goes on to say that the caster need not sense their target. Going back to the main rule book the requirement is that the caster perceives the target, knows it exists and generally where it is.
On a computer now, on page 80 of the main rule book, The Limit of Arcane Connection describes a magus using an InIm spell to see behind a wall, and the following it up with a Perdo Corpus spell. Similarly, you can be aware of a room, and cast DEO with a Room Target. Now, you might say that you can't sense the demon, and that might be true, but you can sense the room, but you can never really ever sense the demon, or trust what your sense are telling you, at least.
That's what I get for not doing this for so long.
Perceived but not seen, yes, that's fine.
However... a spell that works at Hearing or Sight or Scent does not extend the caster's range of sensing, just the range of things sensed. A spell that causes a magus to perceive nearby rats as flatulence might work great in a room, but not so great outdoors at a range greater than 20 feet. And if you want to sense animals within a 1 mile radius, even Hearing might not be sufficient, especially if the crickets are chirping and the wind is rustling the leaves...
Also, scent for a human doesn't usually help knowing where it is, just that it is there, somewhere.
A MuCo(An) that provides the scenting ability of a wolf might be sufficient to detect animals in the vicinity.
But the Rego spell still needs an appropriate range, even if it is part of an In spell, and Scent isn't it.
Of course, one is still bounded by the range of the Voice/Sight limitations. But voice normally carries 15 paces, and up to 50 if one is shouting, so 45-150 feet. If your Intellego spell can translate what is sense into Vision, you can then see, and the sight spells will work, which makes the range pretty big.
Being able to sense the target, and it being within the range for your spells is still important, no doubt.
Thus the "compare" word.
What am I comparing?
You premise is that you need to pin-point the target. Nowhere does it say you must pin-point the target. The threshold is that it is sensed.
Then you present Gruagach magic, which doesn't need to sense the target, if the target can hear the Gruagach. Not sure what I am comparing.
Again, if the Hermetic magus can sense the target somehow, and if it is within range of the spell cast, it is affected. If a magus hears a sow rooting around before some brush in the forest, you could cast Agony of the Beast on the beast, if it is within 15 paces, for a normal voice and 50 paces for a shouting voice.
Range pretty big, yet circumstantial. If the animal were already able to be seen, it could be controlled directly in this case. InAn at Sight lets you notice that yup, something you can already see is an animal, or see something about that animal, etc., which can be great for some applications but not this one.