Agrimensor gromam in agro ponit.

Because agrimensor is in the nominative singular, which is the case normally used for the subject.

Also, the verb ponit is third person singular, so it matches a singular subject: agrimensor = the surveyor.

So the basic structure is:

• agrimensor = subject
• gromam = direct object
• ponit = verb

Because it is the direct object of the verb ponit.

The verb pono means put, place, set down, and the thing being placed takes the accusative case.
So:

• groma = nominative singular
• gromam = accusative singular

This tells you that the surveyor is placing the groma.

Because in can take two different cases depending on the meaning:

• in + ablative = in / on a place, showing location
• in + accusative = into / onto a place, showing motion toward

Here, in agro means in the field, so it describes where the groma is being placed. That is why agro is ablative singular.

Compare:

• in agro = in the field
• in agrum = into the field

Ponit is:

• third person singular
• present tense
• active voice
• indicative mood

It comes from the verb pono, ponere, meaning to place, to put, or to set.

So ponit means he/she/it places, or sometimes is placing.

Yes. Latin present tense often covers both ideas that English separates:

• he places
• he is placing

Context usually tells you which English wording sounds best.

So Agrimensor gromam in agro ponit could be understood as either:

• The surveyor places the groma in the field
• The surveyor is placing the groma in the field

Because Latin has no articles like English the or a/an.

A Latin noun by itself can often mean:

• a surveyor
• the surveyor

and similarly:

• a field
• the field

You choose the best English article from the context.

So agrimensor does not itself tell you whether to translate a surveyor or the surveyor.

Latin word order is more flexible than English word order because the endings show the grammatical roles.

This sentence uses a very common Latin pattern:

• subject first
• object next
• other phrase(s)
• verb last

So:

• Agrimensor = subject
• gromam = object
• in agro = prepositional phrase
• ponit = verb

Putting the verb at the end is extremely common in Latin, but other orders are possible too. For example, Latin could rearrange the words for emphasis and still keep the same basic meaning, because the cases tell you what each noun is doing.

A groma was a Roman surveying instrument. It was used to lay out straight lines and right angles, especially for measuring land and planning roads, towns, or fields.

That is why it appears naturally with agrimensor, which means land surveyor.

So this sentence has a specifically Roman feel: a surveyor is setting up his measuring instrument in a field.

Agro is ablative singular.

Its dictionary form is ager, meaning field.
The main singular forms are:

• nominative: ager
• genitive: agri
• dative: agro
• accusative: agrum
• ablative: agro

In this sentence, agro is ablative because it follows in with the meaning of location.

Agrimensor is a third-declension masculine noun.

Its genitive singular is agrimensoris, which is the form you would see in a dictionary entry. So a full dictionary form would be something like:

• agrimensor, agrimensoris = land surveyor

The ending -or is common in Latin agent nouns, especially ones describing a person who does something.

Approximately like this:

• agrimensor = ah-grih-MEN-sor
• gromam = GROH-mahm
• in agro = in AH-groh
• ponit = POH-nit

A few helpful points:

• g is always hard, as in go
• vowel sounds are more steady than in English
• the stress falls on -men- in agrimensor

So the whole sentence would sound roughly like:

ah-grih-MEN-sor GROH-mahm in AH-groh POH-nit

Yes, depending on context.

The verb pono basically means put or place, but in real translation English sometimes prefers a more natural phrase such as:

• places
• sets down
• sets up

Since a groma is an instrument, sets up may sound especially natural in context. But grammatically, the Latin verb itself is still simply ponit, from pono.