The part of a sentence "considered impossible to" is correct and usable in written English.
You can use it when you want to express the idea that something is thought to be impossible to do. For example: "The task was considered impossible to complete in the amount of time given."
But hardly anyone fishes for them because they are widely considered impossible to catch.
Women who can feel sexual pleasure are considered impossible to control and so are unmarriageable.
(A resolution was considered impossible to pass, as indeed it was).
But in Europe, for centuries before d'Entrecolles's observations, the arcanum of porcelain was considered impossible to unearth.
The race is complicated and considered impossible to predict, since so many of the candidates have such important support.
In too many accounts, blame is considered impossible to assign given the complexities of modern-day finance.
On the basis of the relevant heterogeneity founded in the included studies, we consider impossible to conduct a meaningful meta-analysis of data.
Prior to Akasaki's work in the 1980s, scientists had produced LEDs that emitted red or green light, but blue LEDs had been considered impossible or impractical to make.
Here are the results of such an exercice where a question was posed about what is considered impossible today and to the time horizon of several decades ahead as well.
Thinking about impossible futures is a brain teaser to stretch one's imagination; what is now considered impossible can turn out to be possible in the future.
In 1909, the Boston Medical and Surgical Journal noted that by the eighteenth century rhinoplasty "sank into disuse and in course of time began to be considered impossible or fabulous".
