Artur Wieladek, 42, of Osborne Road North, Southampton was seen with his trousers down on the outskirts of Totton precinct.
Wieladek was ‘moving his right hand backwards and forwards’ as he watched people in the precinct, Southampton Magistrates’ Court heard.
He then walked away as a couple approached him from the car park.
Prosecuting, Mr Anthony McCafferty called the pair as witnesses.
Giving evidence, one of the witnesses said her recollection of the incident in the morning of June 11 last year is ‘unfortunately quite clear’.
She said: “We walked past the toilet block towards the precinct, and a metre or so after we passed it my husband said, ‘can you see that gentleman?’
“I thought it was a strange thing to be doing in a public place. He was facing us but looking towards the precinct where people were sat.
“It didn’t look like something you would be doing when going to the toilet, and I didn’t see any urine.”
She added: “The thing I found the strangest is that if he did need to go to the toilet, he was facing the toilet block that was not even 10 metres from where he stood.”
The pair had no doubt Wieladek was pleasuring himself rather than urinating as they had ‘an unbroken line of sight’.
The second witness said: “We saw him pleasure himself for about five seconds, long enough for me to be satisfied that’s what he was doing. It’s very clear in my mind.”
The pair called the police and officers arrived shortly after.
Wieladek, who represented himself in court, previously pleaded guilty to outraging public decency.
But this was on the basis that he was urinating, not pleasuring himself.
He also pleaded guilty to criminal damage by urinating in the back of a police van following his arrest on June 11 last year.
Solicitor Tim McGoldrick, who was appointed by the court, told the witnesses at the Newton hearing what they saw was ‘the end of a wee’ and a man ‘shaking himself dry’.
Chairman Miss Hampton said: “We have found the two witnesses to be very credible.
“They were not word perfect and they were confident in their shock at what they saw.
“We definitely believe that the Crown has proved the case beyond all reasonable doubt.”
Wieladek will appear before Southampton Magistrates’ Court on October 18 to be sentenced.