Presuming you are looking at the Australian situation, STODA replaced the old term EOL (effective operational length) eons ago.
Basically, the operator needs to know distances which will fit with the aircraft's performance requirements. Where the TODA EOS gradient is excessive, the runway STODA data provide reduced runway effective lengths which are associated with standard gradients.
For example, I picked one out of the ERSA RDA
Albany.
R05, for instance, has no STODA data declared as the TODA EOS gradient presents no problems for heavy aircraft (forgetting first segment, which sometimes is a problem, the second segment WAT for heavy twins is 1.6 % net which is covered quite nicely by the 1.2% EOS gradient declared). Similar story applies for R14.
R23 and R32, on the other hand, present problems for TOD calculations determined by TODA so the standard STODA gradient distances are declared under the STODA figures.
In essence, TODA and STODA are similar. STODA provides effective TOD data for standard obstacle free gradients from the end of the relevant distances. TODA provides whatever obstacle free gradient is available at the end of TODA.
While the data can be determined by inclino survey, most would be calculated directly from Type A survey obstacle data.