Plaintiff Hill instituted this action in ejectment and recovered a judgment against defendants. By this appeal defendants contend that the evidence was insufficient to submit the question of plaintiff’s title to the jury and that the trial court erred in failing to instruct the jury upon the question of estoppel.

The extensive record in this case reflects a material difference of opinion between the respective surveyors for plaintiff and defendants. Each of the surveyors was qualified, and since their testimony was in conflict, the question was a proper one for consideration by the jury. The evidence as a whole fails to support defendants’ theory on this appeal as to the question of estoppel. Furthermore, defendants failed to plead in accordance with *744the Florida Rules of Civil Procedure, Rule 1.110(d), 30 F.S.A., the affirmative defense of estoppel, and under these circumstances we hold that the trial judge was not in error in refusing to grant defendants’ requested instruction on the doctrine of estoppel. Our review of this record reflects that the issues were joined, the case fairly tried, and the verdict of the jury is supported by competent substantial evidence. It is not the function of an appellate court to substitute its judgment for that of the trial court.

The judgment appealed is affirmed.