#Dyalog APL , 63 bytes

s@(n+11 9∘○しろまる ̈+0円j1*⊃ ̈,⍨\(8∘≠⍴ ̈⊢)0,'rdluRDLU'⍳ ̄1↓s)×ばつn←≢s←⍞

uses ⎕IO←0 and features from v16 (@)

n←≢s←⍞ raw input s and its length n

×ばつn create a 2n by 2n matrix of spaces

s@(...) amend the matrix with the characters of s at the specified (pairs of) indices

how the indices are computed:

̄1↓s drop the last char of s

'rdluRDLU'⍳' encode 'r' as 0, 'd' as 1, etc; other chars as 8

0, prepend a 0

(8∘≠⍴ ̈⊢) turn every 8 into an empty list, all others into a 1-element list

,⍨\ cumulative swapped concatenations (abcd -> a ba cba dcba)

⊃ ̈ first from each

0j1* imaginary constant i to the power of

+\ cumulative sums

11 9∘○しろまる ̈ real and imaginary part from each; get coords in the range -n...n

n+ centre them on the big matrix

Dyalog APL , 63 bytes

s@(n+11 9∘○しろまる ̈+0円j1*⊃ ̈,⍨\(8∘≠⍴ ̈⊢)0,'rdluRDLU'⍳ ̄1↓s)×ばつn←≢s←⍞

uses ⎕IO←0 and features from v16 (@)

n←≢s←⍞ raw input s and its length n

×ばつn create a 2n by 2n matrix of spaces

s@(...) amend the matrix with the characters of s at the specified (pairs of) indices

how the indices are computed:

̄1↓s drop the last char of s

'rdluRDLU'⍳' encode 'r' as 0, 'd' as 1, etc; other chars as 8

0, prepend a 0

(8∘≠⍴ ̈⊢) turn every 8 into an empty list, all others into a 1-element list

,⍨\ cumulative swapped concatenations (abcd -> a ba cba dcba)

⊃ ̈ first from each

0j1* imaginary constant i to the power of

+\ cumulative sums

11 9∘○しろまる ̈ real and imaginary part from each; get coords in the range -n...n

n+ centre them on the big matrix