You’ve already made the right choice, because relief is the precise and correct word for what you want. It is pronounced the same way that its homograph is, the one you mentioned being about feelings and such.
The OED lists these two words completely separately. In fact, it has three different nouns here, although the first is obsolete as of the 16th century or so. These words came into all the European languages around the same time, because the literate were frequently literate in many languages and freely borrowed from one another.
† noun¹: c. 1225–1589
Several related meanings connected to scraps left-overs, mostly those from a meal. No longer current. Their etymological notes mention:
Compare Old Occitan releu, Catalan relleu (13th cent. as †releu;
now regional), Spanish relieve (1251; chiefly in plural relieves; now
archaic), Italian rilievo (a1288; now archaic or literary; also as
†rilevo, †relievo), all originally and chiefly in sense 2,
and Middle Dutch relief, relif remainder, (specifically) remains of food
left after a meal (both late 13th cent.). Although in early use the
English word often translates classical Latin reliquiae (plural) (see
reliquiae n.), neither relief n.¹ nor its French etymon are
etymologically related to the Latin plural noun.
noun²: a. 1325–present
This is the more common of the two current meanings. The OED places it in the same frequency band as it places dog, horse, ship, machine, mile, assessment, army, career, which means that it occurs between 10 and 100 times per million words in typical modern English usage. They identify its etymons as (Old) French releef, relief; the verb relieve, and Latin relevium. Specifically they mention:
Probably partly < Anglo-Norman releef, relef, releff, relif, Anglo-Norman
and Middle French relief (French (now hist.) relief) payment made to
the overlord by the heir of a feudal tenant on taking up possession of the
vacant estate (1215 or earlier in Anglo-Norman), formal acknowledgement of
feudal tenure made by a vassal to a lord (13th cent. in Old French),
alleviation (late 14th cent. or earlier in Anglo-Norman; < relever
relieve v.), and partly (especially in later use) < relieve v. In sense
1a perhaps also partly < post-classical Latin relevium relevy n.1; compare
Middle Dutch relief, relif, in same sense (end of the 13th cent.; < Old
French; Dutch (now hist.) relief), and also post-classical Latin
relevamentum (see relievement n.), relevatio (see relevation n.).
This is pronounced the same way as the previous one is, rhyming with belief. The OED places it in their frequency band 5, unlike the previous word which they place in 6. That means it occurs from 1 to 10 times per million words in ordinary English. They mention:
The shift away from the everyday language found in bands 8-6 is apparent in nouns (e.g. surveillance, assimilation, tumult, penchant, paraphrase, admixture)
So it isn't super rare in any way; those are normal words. They identify its etymons as Italian rilievo, relevo, relievo and French relief, and they suggest that one
Compare Spanish relievo (late 16th cent.; < Italian or French), Dutch
reliëf (1659 as relief; < French), early modern German relievo (c1650; <
Italian), German Relief (18th cent.; < French).
As I said, this is the right word to use here. Let me cherry-pick of few of the senses they cite it gets used in today, along with their most recent of many, many citations for each of these I’ve selected.
a. Moulding, carving, stamping, etc., in which the design stands out
from a plane surface so as to have a natural and solid appearance. Also:
work done in this way; the part which so projects. Sometimes with
modifying word specifying the degree of projection: see high relief n. 1,
low relief n., bas-relief n.
- 2008 Edmond (Oklahoma) Sun (Nexis) 4 Oct.
The heaviest object, a marble sarcophagus,..is heavily decorated with carved relief.
c. figurative and in figurative context. Vividness, distinctness, or
prominence due to contrast or method of presentation. Frequently as to
throw (or bring, etc.) into relief.
- 1991 K. Jones Learning not to be First ix. 103
Lizzie became pregnant, and the sickly young woman's fecundity threw Christina's own barrenness into stark relief.
b. Physical Geography. The manner or degree of variation in elevation
of a part of the surface of the earth (or other planetary body).
- 1990 Technol. Rev. Nov. 10/1
Some scientists have said the sharp relief of many mountains suggests these areas have recently grown.
They list many compounds in which this version of relief is used, including: in relief,
and relief tablet. In my own personal experience, relief map is the one of those that I come across the most often.
So this is a perfectly normal word, and I would not hesitate to use it in your technical context.